REVIEW OF SPECTROPHOTOMETRIC METHODS FOR DETERMINATION OF VANADIUM

Behrooz Rezaie, Raziya Zabeen, A.K. Goswami and D.N. Purohit

Department o f Chemistry M .L Sukhadia University Udaipur - 313 001, Rajasthan (India)

CONTENTS Page

REVIEW ...... 1 REFERENCES ...... 200

REVIEW

A survey of literature reported for spectrophotometric determination of vanadium from 1973 to 1991 has been made. To save space the available information has been reported in tabular form. The condensed information is presented under the following headings: name of the reagent, X or working wavelength with e, optimum pH, remarks and references. Under "remarks* information regarding composition of the complex, details of the method, interferences, application of the method, etc., are reported. Shortly before this survey was completed, a review was published (reference 430), covering a significant part of the subject (hydroxamic acid complexes) as studied between 1963 and 1988. There will therefore be some unavoidable overlapping between both reviews.

1 Name of the Reagent X or pH Remarks Refs. working wavelength withe

5 -Dimethylamino-1 - 595 nm 3 J Vanadium forms a (1:1) complex with the re- 1 (2-thiazolylazo) «=42000 to agent and is extracted into CHC13 from aq. phenol 43 medium. Beer’s law is obeyed with up to 1.2 p.g of vol. per mL Interference in the determination of V is caused by Ti(IV), Zr, Nb, Fe(III) and oxalate, but Nb and Fe(III) can be masked with KCN and triethanolamine, respectively. Procedure: To a portion of test soin, containing <10 /tg of V is added 1 ml of 0.01% methanolic reagent, the soin, is adjusted to pH 4 with Na acetate-HO buffer and diluted to 50 ml with HgO and after 15 min. the V complex is extracted into 25 ml of CHClg. The extinction is measured vs. reagent blank extract. To determine V in carbon steel most of the Fe is extracted from the sample with isobutyl ketone. The aq. phase is treated with H2S04 and diluted to 500 ml with H O, then a portion is treated with 2 ml of 0.5% KCN soin, and determination is com­ pleted as described above. For steel containing 0.1% of V, the coefficient of variation was 1%. Antbanilic acid S2S nm 0.2 In aq. ethanolic HgS 04 (pH 0.2 to N in acid), 2 isopropylidene- e = 5100 to V(V) forms a yellow 1:2 complex with the reagent hydrazide Nacid in at least 100-fold amount. The complex becomes cherry-red on addition of acetons in any propor­ tion between 1:4 and 4:1 of original soln. volume, but extinction remains constant Beer's law is obeyed for 3 to 100 /ig of V per 25 mL There is no interference from 10,000 fold amount of A1 or al­ kali, alkaline-earth or rare earth metals, 500-fold amount of H , Zr, Sc, Zn, Mn, Ga, Ge, or Cr, 200- fold amounts of U, Th, Nb, Ta, Cd, Fe, Cu, Co or W o r 3500-fold amounts of Mo, or In, but Os and BrOa must be absent. To determine V in silicates, the sample (1 g. containing down to 6.5 ppm of V) is dissolved in HNOg- H a (1:3) in the presence of aq. HaOa, the soln. is filtered through paper pulp, and the residue is washed with 1% HNO. and the 3 hot filtrate is treated with aq. NHg in slight excess. The ppt. is collected and washed with 1% NH^NOg soln. and dissolved in 50 ml of N-H SO. and 10 ml of soln. is treated with 1.5 ml of H3P 04 and then oxidised with 0.5% KMNO^ soln.; unconsumed KMN04 is decomposed with 0.05% of reagent in acetone, is added, the mixture is diluted to 25 ml with acetone and its extinction is measured. The calibration graph covers the range up to 10 of V. Name of the Reagent X or Remarks Refs. m ax. PH working wavelength withe

3-Hydroxy-l-3-diphenyl All complexes are yellow-green and their compo­ 3 triazene and its sition (reagenfcmetal) is 1:1. All are water soluble derivatives except the first (a) which is soluble in water- ethanol. ■ - i a) 3-Hydroxy-l,3- 410 nm 3.1 Beer’s law is obeyed in the range of 0.25 to 10 diphenyl triazene «=5875 to ppm. The value of Sandell’s sensitivity is 0.085 4.2 jig/cm2. . b) 3-Hydroxy-3-phenyl 400 nm 3 3 Beer’s law is obeyed from 0.25 to 10 ppm. The 2 -1-p-sulphonato- «=5875 to value of Sandells’ sensitivity is 0.0085 /tg/cm . phenyltriazene 4 3 (Na. salt) c) 3-Hydroxy-3-phenyl 400 nm 3 3 Beer’s law is obeyed in the range 0.25 to 10 -1-o-sulphonato to ppm. The value of Sandell’s sensitivity is 0.026 phenyltriazene 43 /tg/cm2. (Na. salt) d) 3-Hydroxy-3-phenyl 400 nm 3.6 Beer’s law is obeyed in the range 0.25 to 12 -1-m-sulphonato «=5250 to ppm. The value of Sandell’s sensitivity is phenyltriazene 4.6 0.0095 /xg.cm2. (Na. salt). e) 3-Hydrc*y-3-phenyl 410 nm 3.6 Beer’s law is obeyed in the range 0.25 to 12 -l-(4-sulphonato- to ppm. The value of Sandell’s sensitivity is 0.05 6-methyl phenyl) 4.6 /¿g/cm2. triazene (Na. salt)

f) 3-Hydroxy-3-phenyl 400 nm 3.0 Beer’s law is obeyed in the range 0.1 to 8.0 -l-(4-sulphonato-5- «=6625 to ppm. The value of Sandell’s sensitivity is methylphenyl 4.4 0.0075 Mg/cm2. triazene (Na. salt). Oxalate, F\ Fe(III), Pd(II), M oO^II), Cr(III) and H(IV) interfere seriously. The fodowing could be tolerated up to the tolerance limit in ppm (given in parentheses): Ni2+ (50); Co2+ (10); MnZ+ (10); WO 2 (20); UO 2* (10); La3+ (30); Ce3+ (20); Zn2+ (100); Cd2* (200); Hg2+ (100); As3+ (100) and Th4+ (40). Cu(II) could be tolerated up to 50 ppm only in presence of Na thiosulphate soln. (1%). U +, Na+, K +, Br', I', Cl', P O ^ , boric arid, citrate and tartrate did not interfere.

Pyrogallo! 610 nm 6-5 At pH 6.5 (610 nm) Beer’s law is obeyed up to 200 « = 7630 /tg of V(V) in 50 ml of soln.. There is no interfer­ 410 nm ence from up to 1 mg of Pd, Ni, Co(U), Sr, Sn(II), « = 4760 Ba, Mn(Il), Mg, Zn or Be or up to 5 mg of Al. The reagent has also been used for determination of u* Ti(IV) and Fe(III) separately and collectively. Name of the Reagent \ or Remarks Refs. m ax. PH working wavelength withe

V(IV) (0.5 to 3.5 ppm) reduces the reagent to its 5 Ferriin [Tris (1,10, 510 nm H 2S ° 4 phenanthroline) medium Fe(II) analogue ferroin in a medium of HgS04 Iron (III)] containing acetic acid to accelerate the reaction, and the extinction of the ferroin is measured. The error is <2%. There is no interference from up to 1 mg of Mn(II), Al, Cd, Co, Mg, Pd(II), Cr(ill), Na, K, or U(\h), up to 50 mg of citrate, Cl’ or acetate or up to 25 mg of PC>4 . Excess of free l,10,phenanthro!ine stabilises the ferroin soln. and particularly eli-minates interference from Cu(II), Ni and Zn.

1^3-Phenyloxy 560 nm Acetic The reagent gives a blue violet ppL with vana- 6 amidine [N-hydroxy- add date ion in acetic add medium and is quantita­ NN’-diphenyl medium tively extracted into CHClg. The absorption benzamidine] max. of the vanadium complex is at 550 to 575 nm and that of the reagent is at 315 nm. The system obeys Beer’s law in the range of 2.4 to 8.8 ppm of V, and sensitivity is 0.011 /tg/cm’2. There is no interference from Fe(II), Mo(VI). Cr(III), Mn(II), Cu(II), Ni(II), Sb(III), or ASC>4 , but Ti(IV) or W(VI) interfere. The result of V determination in two standard steels agreed with the certified value.

Butanol and PAR 545 nrn The test soln. containing up to 20 /rg of V(V), 7 [4-(2-pyridyIazo) is adjusted to pH 3 by adding 1 ml of 0.01M- resorcinol] HNC>3, then diluted to 10 ml with HgO and shaken for 5 min. with 10 ml of 5M-butanol in benzene to extract the V(V). The organic phase is shaken for 5 min. with 10 ml of back-extraction soln. (comprising 5 ml of phosphate buffer soln. of pH 6.4, 2 ml of 0.1% PAR soln. and HgO), and the extinction of the resulting aq. phase is measured vs. HgO. Beer’s law is obeyed over the cited range, and the Sandell sensitivity is 0.0020 ¿ig/cm'2. Slight interference is caused by Co and W(V1), but V(V) is separated from Cr(VI) by this method. The method is used to determine V in rocks (e.g. 23 ppm in granodiorite and 178 ppm in basalt.

N-p-ToIyl-2- 540 nm The 1:2 complex was extracted into CHC13 from 6 8 furohydroxamic acid «=3000 to 8 M-HC1 medium, and its absorbance was measured. Beer’s law is obeyed in the range 0 to 15 ftg of V in the organic phase (25 ml). Extraction into CHC!3 was quantitative in the pH range 0.1 to 2 and the colour was stable for several hours. The method was applied to the determination of V in standard steel and samples of niobium and tantalum. Name of the Reagent X or pH Remarks Refs. working wavelength with«

Tungstophosphale 490 nm 1.1 roM- Tetravalentvanadium foraisa 1:1:11 (V-P-W J 9 h s ° 4 complex with P 04*" and W 04*". The complex is 0.13- formed by hesting on a water bath for 15 min. 1.3 M- under optimum conditions, Le. 1.1 mM-HgP 0 4 and h , p o 4 a > 33-fold molar excess of NagW 04 relative to V. Beer’s law is obeyed for 0.5 to 60 jig/ml of V. 4-(2-?yridytazo) 550 nm 0.4N- The reagent forms a 1:1:1 mixed ligand complex 10 resorcinol ««30000 H SO. with V(V) and hydraxylamine. Beer’s law is obeyed 2 4 for 1 to 8 pg/ml o f V. Rhenium, Th, U , Sn, TI, Mo^ Mn, Al, Be, La, Bl, Cr, Zr and Ca do not interfere but Cu, Fe and W do. The method was used for determining 0.025 to 0.1% of V in uranium alloys and the relalive error was <±35% .

(a) N-Phenyl 530 nm II SO (a) Dissolve 5 g. of sample in 10 ml oTH S 0 4 11 benzohydraxamic (1:4), dilute to 25 ml, to an aliquot add 5 ml of sc id (l) 40% NH4F toln., 1 drop of KMN04 soin. and 50 ml of H JO (1:1), cool, add 5 ml of 0.05% (I) soln. in CHCtj, shake for 1 min. then wash the organic layer and measure the extinction. There is no interference from Cr, or Zr (600); A l, Mn or W (500); Mg or Ca (200); Mo (50) and Nb, Ta or Sn (25) with respect to vanadium. (b) 4-(2-Pyridylazo) 540 nm HQ (b) Dissolve 5 g. of sample in 5 ml of HCI (1:1), resorcinol (II) dilute to 50 ml, and to 2 ml of this add 1 drop of KMN04 soln. 2 ml of 20% NH4-F-HF soln., 1 ml of 5% thiourea soln., 0.5 ml of 1% gelatin soln. and neutralise to methyl red with aq. soln. of II, dilute with water to 15 ml and after 5 min. measure its extinction. Methods with both the reagents are sensitive up to 100 ppm of V, and are used for determination of V in titanium (IV) chloride. There is no need for prior separation of Ti, and the reagent can be used in the presence of fluorides. With either of the methods, a determination takes =* 30 min. and relative error is < 10%.

{2-[3-(-Methyl- 630 nm 4.4 The complex formation is instantaneous and is 2-piperidyl)- «=7700 to complete at optimum pH with a 10-fold molar 2-pyridylazo]- 4.8 excess of the reagent. The (1:1) complex is almost 3,4-xyIenol} completely transferred to CHC13 within 20 to 25 sec. Beer’s law is obeyed for 0.5 to 6 jig/ml of V(V). In determination of 10 fig of V the following do not interfere: >300 fold amounts of Al, Th, Ge, Mn, Cd, Zn, a " and tartrate; 100-fold amounts of Ag, Mo, Cr or Pd; 30-fold amounts of U or Hg; 10- fold amounts of In, Ga or Sb; 5-fold amounts of W or Zr or a 200-fold amount of PO^. In the presence of 0.5 ml of 5% thiourea a 100-fold amount of Cu and a 10-fold amount of Bi, and in the presence of 5 ml of 5% NaCl soln. a 50-fold amount of H are tolerated. O Name of the Reagent Remarks Refs. Xm ax. or PH working wavelength with e -

bis-(2-sulpho- 655 nm V(V) forms with this reagent a (1:1) complex 13 ethylamino) e=10800 which is stable for 3 hr, and is extractable into gosspol (sodium organic solvents. Photometric determination salt) of V in the presence of e.g. Fe(II), Co(II), W(VI), In(IlI) and U(VI) has been reported.

1,10-Phenan- 510 nm 5 Vanadium in rutile was separated from Ti and 14 throline Fe by fusion with Na2COg, leaching the cooled melt with l-HD, filtering the soln. and acidifying the filtrate with HC1. Silicate samples were decomposed with HF, H Q , and Fe was removed by extraction (as chloride) into ethyl-ether. The V(IV) in the H Q soln. was reduced to V(1V) with HgSO^. The V(IV) was caused to react with Fe(III) (in excess) at pH 5 in the presence of 1,10- phenanthroline, and the extinction of Fe(II)-l,10- phenan-throline complex was measured.

N-m-Tolyl-2- 550 nm 6 to Test soln. (10 ml) prepared by the method of Shapiro 15 methaxy benzo- e=6400 8-M and Brannock is shaken for 10 min. with 10 ml of 6 hydroxamic acid HQ to 8 M -HQ and 5 ml of 0.1 reagent The violet CHQ 3 layer is separated and the aq. layer is again extracted with reagent soln. (2x5 ml). The com- bined extracts are dried over NagS04 which is then washed with CHG3 (3x2 ml). The extract plus washings are diluted to 25 ml with C H Q 3 and extinction is measured against CHC13_ Beer’s law is obeyed for 0.05 to 15 jig/ml of V. The method can be applied in the presence of Be, Cr, Ni, Cu, Ti, Co, As, Mo and rare earth metals.

O-Phenylene 400 nm 2.5 A method for determination of V in steel has been 16 diamine to reported. EDTA and oxidizing agents interfere and 3.2 a separation of V(V) from Fe has to be made before determination.

N-Phenylbenzo- 530 nm 3M- Microdetermination of V in sea water has 17 hydroxamic acid HCt been reported after removal of Fe. Vanadium is oxidised to V(V) and the soIn. is made 3M in HCI, extracted with 0.1% reagent in CHC13 and absorbance is measured against HgO. Recoveries were 93.6 ±2.1% for V content of 0.8 to 134 /ig/1.

N-Phenyl-2-naptho- 545 nm 7M- Add5mlof7M-HClto5mlofV(V)soln.(= 3 18 hydraxamic acid HCI mM), extract for 5 to 10 min. with 5 ml of 0.1% (w/v) of reagent soln. in CHCl^. Dry the separated organic phase over NajSO^, dilute it to 25 ml with CHClg and measure thè extinction against a reagent blank. The method for determination of V in five standard steels has been applied and results agree with the certified value. N> Name of the Reagent X or pH Remarks Refs. max. working wavelength withe

3-Methyl catechol 610 mu' 7 The blue ion pair complex is extracted from aq. 19 and Dodecyltrimethyl- systems into 1,2-dichloroethane. The aq. soln. is ammonium bromide neutralized to pH 7 with Na2 SO^ which stabilises the system against oxidation. .The quaternary ammonium salt also has a stabilising influence and 3-methyl catechol should be present in large excess. Iodide salts should not be used, as I* catalyses oxidation of the system. The ratio of V(IV) to 3-methyl catechol to dodecyltrimethyl ammonium bromide is 1:4000:200. Under such conditions V(IV) (50 /¿M) can be determined in the presence of a 45-fold excess of W(VI).

2-(3,5-Dibromo- 615 nm Acidic Vanadium (V) forms a blue (1:1:1:) complex with 20 4-methyl-2- e=54300 this reagent and H20 2- The complex is extractable into CHC1 and its absorbance can be measured. pyridylazo)-5- 3 diethylaminophenol In presence of F" the reaction is highly selective for V(V). Only large amounts of other halides or of oxidising or reducing agents interfere. Using this method V(V) in silicate rocks samples has been determined and the values obtained were found to compare well with accepted values. 4-(2-PyridyIazo) 560 nm VC>2+ forms a 1:1:1: complex with both reagents 21 resorcinol and «=37000 in soln. of pH 4.5 to 6. The complex is extracted into CHC1, and the absorbance of the extract is nitron 3 measured. Beer’s law is obeyed for 0.3 to 6 pg of V in 5 ml. Aluminium, Mg, Ca, W, Zr, Mn, Cr, Mo, Nb, Ta, Sn, SO*' and CN' do not interfere; Ti(V) can be masked by NH^-HF and Fe(lII) by thio­ urea. The method has been used for determination of < 1 ppm of V in 3 ml samples of titanium tetra­ chloride. The coeff. of variation <9.8% (5 results).

7-(a-Anilino- 390 om Reagent forms a red coloured (1:1) complex 22 benzyI)-8-hydroxy with VOa+. Absorbance was measured in 50% di- quinoline oxane at 30 ± 1"G Stability of the complex has been reported as 3.0 x 104 in 50% aq. dioxane (v/v).

Hexacyanochromate 400 nm A 10 mM soin. of p-anisidine (2J5 ml) or p- 23 (III) with p- phenylene-diamine hydrochloride (5 ml) is mixed anisidine or p- with 10 mM-KgCr(CN)e (2J> ml). The 10 mM phenylenediamine metal salt soln. (1 ml) is added, and the soln. is hydrochloride diluted to 50 ml with a buffer soln. of pH 3. An aliquot is diluted to 10 ml with the same buffer soln. and extinction is measured. A calibration graph is prepared similarly. The procedure avoids the need for u.v. irradiation that is associated with g . the use of Cr(CN)a only as reagent. The reagents have also been used for determination of Be(II), Hg(II), Cr(IlI) and Mo(VI). Name of the Reagent A. or Remarks Refs. m ax. PH working wavelength with e

Mercapto- 600 nm 4 Vanadium in gas-turbine fuel oils has been de- 24 acetic acid and termined. The oil sample is digested with tannic acid H2SC>4, the digest is ashed at high temp, and dissolved in HC1-HNO . The soln. is diluted with a HgO, neutralised with aq. NHg, pH adjusted to 4 with acetate buffer soln. and then the reagents are added. Extinction of the intensely indigo-blue complex formed between V and the reagents was measured. Beer’s law is obeyed in the range 0.5 to 5 ppm of V. Common mineral constituents in the type of oil analysed do not interfere.

Thymolphtbalein 610 nm 2.5 Complexan forms a (1:1:1) complex with V(V) 25 complexan, and «=5740 to and F* in 40% aq. acetone at pH 2 J to 3.4. fluoride 3.4 Beer’s law is obeyed for 0.51 to 16.3 /¿g/ml of V [ = 150-fold molar excess of F relative to V(V) is needed]. A 2-fold amount (molar) of Mo(VI), a 5- fold amount of W(V1) or Cr(VI), a 10-fold amount of Fe(lII), a 50-fold amount of Zr(IV), a 75-fold amouqnt of Ti(IV) or a 100-fold amount of Cr(lll) (relative to V) does not interfere, but ascorbic acid, oxalic and mercaptoacetic acid interfere. The method has been adapted for determination of V in steel, see following reference. Thymolphthalein 600 am A method for determination of V in steel has 26 completan been reported. The sample (0.5 to 1 g) is dissolved in 10 to 15 ml of H O , 2 to 3 ml of HNOg is added, filtrated if necessary, the filtrate is evaporated to a syrup, bon is removed by washing the syrup with ethyl ether, and traces of V also removed are back extracted into H Q (4x5 ml) said, with ether and containing a few drops of 30% aq. the combined H Q soln. is heated to expel ether and then evaporated to near dryness. The residue is treated with 1 or 2 ml of HNO. to oxidise V, then 5 ml of M -HQ and 4 ml of M-Na acetate are added and diluted with HzO to 50 ml. A portion (1 to 4 ml) thereof is treated with 10 ml of acetone, 2 ml of 3% NaF soln. and 1 ml of 1% complexan soln. and the mixture is diluted to 25 ml with aq. buffer of pH 25. After 5 to 8 min. extinction was measured at 600 nm.

1-Naphthol and 345 nm To 2 ml of sample sqln. (0.2 to 3 fig of V) add 5 ml of 27 p-phenylene 0.IM-KQO3, 5 ml of 0.2% 1-naphthol soln. in 50% diamine-hydro­ isopropyl alcohol, 5 ml of 0.3% aq. p-phenylene chloride diamine hydrochloride and 7.5 ml of H O-K Q buf­ fer soln. at pH 2 2 and dilute the soln. to 25 ml. Heat the soln. at 80* for 10 min., cool and measure the extinction. Beer’s law is obeyed for 0.008 to 0.12 fig/ml of V. Interfering elements are removed by a double extraction of the V-8-hydroxyquinoline complex into CHQ a at pH 4.2 to 45. O n Name of the Reagent or Remarks Refs. X.m a x . PH working wavelength withe

2-Ethoxycarbonyl L 478 nm 1 The reagent has been used to determine V(V) 28 5-hydroxy-l-(4- and at different wavelengths and corresponding pH to!yl)-pyridin-4- ii. 615 nm 4.5M- values, (i) Adjust the pH of 10 ml of test soln. one.’ HQ (containing 10 to 150 ftg of V(V)] to 1 with H Q, HNO. or H SO . extract for 2 min. with 5 ml of 5 3 2 4 mM reagent in C H G 3. Separate the organic phase, extract the aq. phase with 4 ml of CHC13. Dilute the combined CHClg extracts to 10 ml and measure the extinction, (ii) To 1 ml of test soln. [containing 10 to 150 ¿tg of V(V)] add 4.5 M-HCI (with other acids the desired blue colour is not formed). Dilute the soln. to 10 ml. Extract for 2 min. with O.OlM-reagent in CHCI3 (2x3.5 ml) and measure the extinction.

N-Phenyl-benzo 475 nm A method for determination of ultra trace 29 hydraxamic add amounts of V, Ti, Fe and A1 in fused silica has inCHCl been reported. In a sequence Ti, Fe, V and A1 have 3 been extracted separately with different extrac­ tants. For determination of V the said reagent was used. The results were reported to compare well with those obtained by other techniques. 3-Hydroxy-2- (I) 497 nm 1.0 Complexes of different composition are 30 methyi-l-[henyl- «=4100 to different pH values with different X . At pyridine-4-one (11) 625 nm 2.2 pH 1.0 to 2.2 the spedes is VOg X.HX with (HX) «=5600 0.75 X .at 497 nm, at 0.75 to 1.25 M-addity in m ax to presence of excess of Cl the spedes is VO O 1.25M (HX)2 with X at 625 nm and at 0 3 to 0.4 (H +) M-addity in presence of excess of CIO^ the spedes formed is VO Q O, (HX) with X at r 2 4 v ^3 max, 605 nm. The spedes are extractable into CHO^ Vanadium has been determined both at 497 nm and 625 nm under respective pH conditions. At 497 nm U(VI), Ti(IV), Zr, Ga, Ta, Nb and Fe(m) are reported to interfere.

N-Phenyi- 535 nm 4M- Reagent forms a complex with V(V) that is ex- 31 cinnamo- «=6300 H Q tractable into CHQa from aq. 4M-HCL A 10- hydroxamic fold molar excess of reagent relative to V is add needed. Absorption of the extract was measured and Beer’s law was obeyed for 03 to 10 jxg/ml of V. A 10-fold amount (with respect to V) of Ti, a 20- fold amount of Mo and a 900-fold amount of Zr, Al, Ba, Cd, Ce, Ca, Co, Cr(III), Cu, Fe(lII), Hg, Mn(II), Ni, U, W, Zn, acetate, borate, citrate, tartrate, P0^3+, SO^2 do not interfere, but NO? and Cr(VI) do. The method is used for deter­ mining 0.2 to 2% of V in steels containing Cr, Ni, Cu, W, Mo, H , B and Co; the coeff. of variation was 5% (7 results). Name of the Reagent X or Remarks Refs. m a x . working wavelength withe

2,9-Dimethyl-l,10- 430 nm Reagent forms with V(II) in aq. acetate-Cf buffer 32 phenanthroline e—1140 medium of pH S.2 to 6 a violet complex and in the same buffer of pH 4.2 to 4.9 a yellow complex which in fact is a V(IV) complex. The V(II) is oxidised to V(IV) during complex formation and need not be protected from atmospheric oxygen. Absorption was measured and Beer’s law is obeyed from 0.1 mM to 2.0 mM-V(Il), Equivalent am­ ounts of V(I1I) [relative to V(II)] and up to 80-fold molar amounts of Mg and Al, a 40-fold amount of Pb(H) and 8-fold amounts of Cd, Mn(H), Co(H) and Zn do not interfere; Fe(ll) can be masked by citrate, and the yellow complex of V(IV) can be extracted into dichloroethane.

Pentavalent V forms two complexes with this 33 reagent, one with an excess of reagent at pH 6.5 having a reagent to metal ratio of (2:1) and max. absorption at — 525 nm and one with an excess of V(V) at pH 4.5 to 5-5 having corresponding ratio of (1:2) and max. absorption at — 610 nm. Poly­ meric vanadates because of introducing error should first be destroyed by boiling the test soin, with NaOH at pH 11 to 12 for 15 min. The soin, is cooled, to a portion containing 50 to 500 fig of V are added 10 ml of 0.01 M of the reagent, and 10 ml of acetate buffer soln. of pH 6.5, and the vol. is adjusted to 100 ml. After 20 min. extinction is measured.

4-(2-Pyridylazo) 545 nm 6 The sample is decomposed, insoluble material resorcinol to fused with LiBCK The test soln. in 0.1 to 0.2M- HC104, containing 0.05% of H20 2, is applied to a column of AG 50W-X8 resin (200-400 mesh), and elution is effected with 0.01-HNOg containing 0.15% of H2Oz- This separates V(III) from e g. Al, Fe(III), Ti(IV), Ca, Mg, Mn(II), Na and K. The total percolate is concentrated, S02 is passed through the soln. reducing V(V) to V(IV), and this soln. is applied to a second AG 50 column (pre­ equilibrated with 0.1M-HC1C>4 containing SO\ from which McV(VI) is eluted with 0.1 HCIO^ containing SOg. The column is then washed with 0.1M-HClO4 to remove the SOg and V is eluted [as V(V)J with 0.01 M HNOg containing 0.15% of H2Og. A portion of this eiuate is evaporated with HC104 and Na2S 0 4, the residue is dissolved with 0.2M-HC104 plus S20 82'. After adjusting the soln. to pH 6 to 7, vanadium (V) is determined; Nb(V) and Mo(VI) do not interfere. V can be determined up to 1 ppm in 1 g sample of standard silicate rocks with a coeff. of variation of = 5% (3 to 6 determinations). For samples low in Nb, a single column procedure can be used. t o O Name of the Reagent k or Remarks Refs. m a x . PH working wavelength with«

4-(2-PyridyIazo) 585 nm 4.8 A sample containing 1 to 5 ¡ig of V is wet- 35 resorcinol (PAR) ashed with HN03-HC10 ; after evaporation and crystal violet of the acid, 0.2 ml of 0.1% Ce(SC>4)2 soln. is [CL Basic added. After 5 min. the mixture is made 4 M in Violet] HO and extracted with N-phenyl benzo- hydroxamic acid soln. in C H O a (2x5 ml). The extracts are washed with 5 ml of 6M-HO and CHClg is removed by evaporation; the residue after ignition is gently heated with 0.5 ml of 0.1M- NaOH and 5 ml of H O. After cooling the soln. is treated with 1 ml of 0.5 mM-PAR, the pH is adjusted to 5, then 2 ml of phosphate buffer soln. of pH 4.8, 1 ml of mM crystal violet and 8 ml of benzene-isobutyl methyl ketone (3:2) are added. After shaking the organic phase is added to 1.5 ml of ethanol, the vol. is adjusted to 10 ml with the extraction solvent and extinction measured. Deter­ mination of V content in Omithopus, rye straw, rye grain and trifolium spp. has been reported. Hydrazinium 460 nm Reagent forms soluble, coloured 2:1 complex 36 hydrazin carbo- «=1100 with Fe(Il) and V(V) in aq. medium of pH 4 to dithioate 6. The Fe(II) reagent complex is determined at 570 nm («=2800), and Beer’s law is obeyed for 10 to 300 pg/ml of Fe; a — 10-fold molar excess of the reagent is needed. The V(V) complex has been measured; Beer’s law is obeyed for 50 to 300 pg/ml of V; a = 20-fold molar excess of reagent is needed. This complex has been used to determine 7.6 to 42 ppm of V in Black Sea shelf sediments; the coeff. of variation was <4.5% (5 results).

Salicylo- 470 nm The test soln. derived from a sample of soil or 37 hydraxamic mineral, containing » 4 ppm of V, is shaken acid with KC1-HC1-buffer soln. of pH 1 and 0.01M reagent soln. in isoamyl alcohol for 5 min, then the separated organic layer is dried with Na2SC>4 and made up to a known vol. with reagent soln. and its extinction is measured against a reagent blank. There is no interference from 500 ppm of Hg(II), 200 ppm of Al, Mg or Ca, 100 ppm of Cu(ll), Co, Cd, Be, Ni, or Zn or 50 ppm of Pd(II), Mo(VI), U(VI), Sn(Il), Cr(II), Mn(II). Also, 2-chIoro-N- phenyl acetohydroxamic acid soln. in CHC13 can be used as reagent; extraction in this instance is carried out at pH 3, and measured at 430 nm. Name of the Reagent \nax.or pH Remarks Refs. working wavelength withe

N-Phenyl benzo- 530 nm 10% Sample is decomposed by fusion with Na2CC>3- 38 hydraxamic add (W/V) KgC 03-H3B 03 or (for feirochromium alloys) HQ with Na20 2-Na2CC>3 and in an H2SC>4 soln. of the melt, Cr(VI) is reduced to Cr(IIl) by Fe(II). Surplus Fe(II) is oxidised with KMnO^, HCI is added to a concn. of = 10% (W/V) and V(V) is extracted into CHC13 as a complex with reagent. Extindion of the extract is measured and referred to a calibration graph for the range 0.025 to 0.2 mg of V in 25 ml of extract. Results obtained on seven chromite samples agree well with other methods.

N-2-Methoxyphenyl- 540 to 3 A soln. 0.5 mM in V(V) and 3 to 6 in HCI is 39 2-thenohydraxamic 550 nm to mixed with an equal vol. of a 0.05 M soln. of add «=7200 6M-HQ the reagent in CHC13 and the violet complex is extracted into the CHC13 phase. The absorption of the extract is measured and Beer’s law is obeyed with up to 15 itg/tnl of V(V). Metal species and ions including those normally associated with V [4.g. Ti(IV), Fe(III)t U(VI), La, Ca, F' and P O ^] were tested for interference; none was found, even with ratio to V(V) as high as 1000:1. 3- Hydroxy-2-methyl 500 nm 1.2 to 2.5 The reagent (Hy) forms three complexes with 40 l-(p-tolyl)- 625 nm 1.2 to Z0 V(V). At pH 1.2 to 2.5, an orange complex 4- pyridone M-HQ CO^.Hy, at pH 1.2 to 2.0 M-HCl, a blue com­ 605 nm 0.2 to 1.0 plex VOaCl(Hy)2, and a blue complex M-HCl V 0 2C104(Hy)3 in 0.2 to 1.0 M-HC1C>4. Beer’s law is obeyed for I to .10 /ig/mi of V. Application of complexes and effect of foreign ions are discussed.

4- Benzoyl-3-methyl 500 nm 0.2 N-HC1 The V(V) forms a complex with named 41 1-phenyl pyrazolin- «=2320 reagent that is extractable from aq. medium 0.2 N 5- one-isopentyl in HCI into CHQ 3. Absorption of the extract is alcohol measured, and Beer’s law is obeyed for 2.5 to 20 /tg/ml of V(V). Up to 500-fold amounts [(with respect to V(V)J of V(iV), Cr(III), or Al, 1000- fold amounts of Ca, Mg, Ba, Zn, Co, Ni, Cu or Mn(II), a 10-fold amount of Fe(III) and a 20-fold amount of Zr do not interfere, but Mo(VI), W(VI), Ti(IV) and reducing agents do. The method was used for determining 3.90% of V(V) in the presence of V(IV) in a catalyst having a silica matrix. The V(V) and V(IV) were extracted from the catalyst (O.lg) by hot 0.2N HCI and one portion of the extract analysed for V(V); in an­ other portion V(IV) was oxidised to V(IV) with KMnO , the total V was determined and the con- 4 tent of V(IV) was calculated by difference. The coeff. of variation was 0.25 for V(V) and 5% for V(fV) (3 results). to Name of the Reagent X o r pH Remarks m ax. r working wavelength withe

N-(4-ChlorophenyJ)- 545 nm 6 The V(V) is extracted from 6 to 8M-HC1 soln. 4-methoxy-benzo to with a 0.5% soln. of the reagent in CHC13, and hydraxamic add 8M-HC1 the extinction of extract is measured against pure solvent. Beer’s law is obeyed for 0.5 to 15 ppm and sensitivity is 9 ng cm'2. The effects of foreign ions are listed.

Tribromopyrogallol 600 nm 05M- To the sample soln. (1 ml) is added 0.5-H2SO4 (2 ml) and then diluted to 10 ml and shaken HaS°4 for 2 min. with 25% of trioctylamine soln. in benzene (10 ml). To 5 ml of the organic phase is added 1 ml of 2% reagent soln. in ethanol and extinction of the blue soln. is measured. There is rectilinear relationship between ex­ tinction and V concn. in the extract, in the range 05 to 1.4 /ig/mL There is no interference from V(IV), 100-fold excess of Mn, Cu, Ni, Zn, Cd, Al, Co, Zr, Ti, or W or a 2-fold excess of Mo. Ascorbic add, dtric and trihydroxy glutaric add and EDTA interfere; Fe(III) interferes but can be masked with NH F or 4 4-DimethyIamino-2- 410 nm 4 To the add test aoln. (5 ml) are added 3 ml of 44 nitrosophenol «=14000 an aq. soin, of reagent (40.5 mg/dl) and (in hydrochloride silicate rock analysis) 1 ml of 0.5M-NaF; the soin, is adjusted to pH 4 with acetate buffer soin., then diluted to 25 ml and extinction is measured. Beef’s law is obeyed for un to 2 /¿g/ ml of V. Fluoride, SiO^" and CrO^ ' can be tolerated in limited amounts and other com­ mon anions in concn. up to 2 M; some heavy metals interfere seriously, and tolerance to A1 is limited. When the method was applied to the determination of V in a sample prepared to simulate silica rocks, Fe, Co and Ni were first copredpitated with MnO,,. Results for V in three standard rocks were in agreement with accepted values.

N-(4-Dimetylamino- 570 nm 4 to To a 5 ml portion o f 0.5 fiM to 0 5 mM - V(V), 45 phenyl)-3-methaxy- 10 were added 5 ml of 4 to 10 M -HQ and 5 ml of 2-naphthohydraxamic M-HCl 0.1M reagent soln. in CHC13 (ethanol free) acid and the mixture was shaken for 5 min. The separated organic phase was dried over Na2S04, the aq. phase re-extracted and the dried organic phases combined. This extract was diluted to 25 ml with reagent soln. and extinction measured against a blank. Beer’s law is obeyed in the range 0.15 to 8 5 /xg/ml of V(V). Method applied to determination of V in ilmenite, phosphate rocks and steel. ts > Name of the Reagent pH Remarks Refs. Xm ax. or working wavelength withe

2+ Eriochrome black T 570 nm Z4 to 4 The chelate formed between VO and the 46 and named dyes have a ratio of (metal ion to lig­ Solochrome black 580 nm 2.4 to 4 and) 1:Z Beer’s law range and Sendell Sen. & 6BN [C.I. Mordant Ringbom optimum range for both complexes black II and 3] are given. Complexes were stable over the pH range Z4 to 4, with max. intensity at 3.8. Potentiometric titration techniques were used to determine the stepwise formation constant.

Isopropylidene- 530 nm 0.5 to 3M Complexes formed between the reagent and 47 hydrazide of e=9600 H2S 0 4 V(V) are extractable into acetone CHC13 (1:1) anthranilic acid from a medium 12 to 1.6M in Na trichloro acetate and 05 to 3 M in H2SC>4; 50-fold molar excess of reagent relative to V(V) is needed. Absorption of extract is measured and Beer’s law is obeyed for 0 3 to 3 /xg/ml of V(V). The following show no interference (amount relative to V): Ti, Zr, Al, Zn, Mg, or POg3" (any amount); V(IV), Mo(VI) or Ni (5000); Ianthanoides (1000); Fe(III) or Cu(II) (500); Mn(VII) or Cr(VI) (100); tartrate or citrate (50,000; oxalate (40,000); F (10,000) or EDTA (2000). This method has been used for determining 3.2 to 120 ppm of V in titanium tetrachloride and titanium concentrates. The coefL of variation was <7.4% (6 results).

4-MethyI-daphnetin 600 nm 5 to 7 Method has been used for the determination [7,8-dihydroxy-4- of V(V) and Ti(HI). In the pH range 5 to 7 re­ methyl coumarin] agent forms a green complex with V(V). An orange complex with H (M ) is measured at 410 nm. Beer’s law is obeyed for up to 2 ppm of V or 8 ppm of T l In the determination of V, there was no interference from 10-fold amounts of Co, Ni, Mg, Sr, Sn(II), No ', N 0 3', SO*, B r , r , Cl', SCN", or FeiCN)^, but Fe(II), Fe(III), ri(III), Cu(II) and BrO." interfered. 3

Gallic add 420 nm 3.8 Up to 120 ng of V(V) can be determined by and bromate oxidation of 53 mM-gallic add with 6mM- Br03* at pH 3.8 and 30" during 15 to 40 min, and measuring the change in extinction. The reaction rate (k) is obtained from the graph of extinction vs. time. The calibration graph of k vs. V concn. is rectilinear and the limit of determination is 0.1 ng/mL The coeff. of vari­ ation was 3.5% for 50 ng and 4% for 20 ng (14 and 10 determinations respectively). There is serious interference from Fe(III) and from > 60-fold amounts of W(VI), Mo(VI), B r'or I". X or Remarks Refs. Name of the Reagent m a x . working wavelength withe

Salicylohydrazide 415 nm In a medium of 50% aq. ethanol at pH 4.0, V(IV) SO e=4000 forms an orange red complex with this reagent and its extinction is measured. Beer's law is obeyed for up to 6 /xg/ml of V(IV). Sandell’s sensitivity is 13 ng cm"2. Barium, U(V1), Mn(II), Sn(ll), Cu(II), Ni, Cr(III), Fe(lII), In and Th interfere. •

8-Hydroxyquino- 560 nm Method used for determining both Fe(III) and 51 Uñates with sodium V(V). Two identical solns. are prepared by dodecyi sulphate adding 1% soln. of the reagent (5 ml) to a soln. containing V(V) (up to 10 ppm), plus Fe(III) (up to 10 ppm); the pptd. complexes are dissolved by addition of 0.62M-Na dodecyi sulphate (4 ml). One sample is adjusted to pH 4.6 and the other to 8, and both solns. are made up to 50 ml with H ^. For determining Fe(III) extinction was measured at 580 nm, and that of acidic soln. at 560 nm, and V(V) was determined after correcting for the Fe(III) content. For each determination the relative error was ± 1% and 2 ppm o f Al, Ni, Cr, Pb o r x Co did not interfere. N-o-ToIy-o- 510 nm -HCI Dissolve the sample in aq. regia, add HC1 to 52 toluhydroxamic HgW 0 4, and then to a 1 ml aliquot add 2 to 3 acid ml of 4% K2Sz0 8 soln. followed by 2 to 3 ml of 8M-HQ. Add 5 ml of a 0.4% of reagent soln. in CHC13 and then 5 ml of CHC13> separate the CHCL3 layer and wash the aq. layer with C H Q 3 (2 x5 ml). Dilute the combined CHC13 extract to 25 ml with CHC13 and measure the extinction. Beer’s law is obeyed for 05 to 10 ml" of V. Concentration of Vis obtained from a calibration graph. Application of the method is to determine vanadium in steel containing chromium, molybdenum, tungsten and manganese.

8-Hydroxyquinolinate 420 to Vanadium (V) is reduced to V(III) by 53 425 nm Na S O and extracted into 2% reagent soln. 2 2 4 in CC1 and extinction of the extract measured i 4 against reagent blank. Beer’s law is obeyed for 7 /¿g/mi of V(III) in the final soln. Sandell sensitivity is 4 ng/cm . Milligram quantities of many elements can be tolerated in 20 ml of final soln. Only Mo interferes seriously. Results are satisfactory for synthetic samples, rutile and ilmenite. OJ O Name of the Reagent \nax.or pH Remarks Refs. working wavelength withe

i) Vanadox [2,2’- 610 nm 12M- Procedure (i): Test soln. (0.25 to 03 g) in 54 iminodi (benzoic H SO 30 ml of HC1-HNC>3 (3:1) is evaporated to acid)] (I) fumes with 20 ml of H2S 0 4 (1:1) and the and residue is heated with 10 to 20 ml of H?0 and 1 o r 2 drops of aq. Hg0 2. The mixture is fil­ tered, insol. material washed with hot HgO and the combined filtrate is diluted to 25 ml with HaO. Selective oxidation of V(IV) in a portion (2 to 3 ml), cooled to 5‘-10°, is carried out conventionally by successive addition of KMn04, NaNOg, and urea soln. The resulting soln. is treated with 10 ml of 12M-H2S 0 4 and 0.2 ml of a 0.1% reagent (J) soln. in Na2COa soln. and then diluted to 25 ml with 12M- H SO . After 5 min. its extinction is measured 2 4 against HgO. Beer’s law is obeyed for 5 to 80 fig of V and there is no interference from 50 mg of Fe(III), Mn(ll), Ni, Co, Cu, Mo(VI), or W(VI), 3 mg of Cr(III) o r Nb(V) or 160 fig of Ca(IV). _ ii) 4-N-Methylani- 490 nm 3M- Procedure (ii): Test soln. (0.25 to 0.5 g) line) benzene H SO in 80 ml of H20-H 2S 0 4-H3P 0 4 (30:10:11), 2 4 sulphonic acid (II) plus a few drops of HNC>3, is evaporated to fumes. The residue is treated with hot HgO and the soln. is diluted to 25 ml with HgO. The V(IV) in 2 to 3 ml of this soln. is oxidised as described above, then 2 ml of HgP 0 4 and 5 ml of mM of reagent (II) are adaed, the mix­ ture diluted to 25 ml with 3M-H2SC>4, and after 5 min., the extinction is measured against HgO. Beer’s law is obeyed for 10 to 120 fig of V and Fe, Mo or W do not interfere.

4-(2-PyridyIazo) 545 nm 5 to 65 Vanadium (V) forms a cationic (1:1) complex resorcinol + «=34500 with this reagent at pH 5 to 6.5, which is used hydrogen and and 1 to determine 0.1 to 1.2jtg/m! of V. At pH 1 peroxide 540 am also, a (1:1) complex is formed with named reagent and after addition of H2C>2 a (1:1:1) complex is formed (V-Reagent-HgO), which could be used in determining H2Og. The HgC>2 was added to a soln. 0.2mM in V(V) and reagent, after 1 hr, extinction was measured against reagent blank. A rectilinear calibration graph was was obtained, for 1 to 65 M-H20 2- Peroxo-acids interfered with determination of HgO by bleaching the reagent. A mechanism for formation of the ternaiy complex is suggested. u> t o Name of the Reagent X or pH Remarks Refs. m ax. r working wavelength with 6

Ferronate[the 8- 430 nm M-H2S04 Vanadium (IV) and V(V) are reduced to 56 hydroxy-7 -iodoqui- V(III) by and a 1:3:9 complex is noline-5-sulphonic formed between V(III)-I. Procedure: To a acid complex] (I) neutral soln. containing < 125 fig of V are and Tribenzylamine (II) added aq. 0.15% of I (12 ml) and 1M-H2S04 (1 ml), and diluted to 20 ml with HzO. Add 0.75 to 0.9 g of Na2S2C>4 and the mixture is shaken in a stoppered vessel for 1 min. and extracted with 2% of (II) soln. in CHC13 (2x10 ml). The combined organic phase is separated and diluted to 25 ml with CHC1 and within 30 3 min. its extinction is measured vs. a reagent blank. If Fe is present, COg is passed through it and through aq. phase before adding Na2S20 4. Beer’s law is obeyed for up to 5 /zg/ml of V. Molybdenum, Ti, Sn, Bi and Zr interfere. The method has been applied for the preparation of alums and high speed steels.

1,10-Phenanthroline 645 nm 8 to 9 The sample is fused with Na2CC>3, the melt is 57 is leached with water and in the soln. a blue complex of V(II) with reagent is produced at 60" to 80" and pH 8 to 9 in the presence of Na S O and the extinction of the cool soln. 2 2 4 measured. Beer’s law is obeyed for V2Og concn. from 033 to 14 /¿g/ml. Method used for determination of V in vanadium titanic magetite and augite.

8-Hydroxy- 620 to Reagent (I) with V(V) forms a dark magenta 58 quinoline (I) 6 4 0 nm complex which turns green when extracted into and Nitrobenzene (II) e= 6 0 1 5 (II) in presence of C104*, NOg or C10g (1:2:2). Of the three anions, CIO^' forms a complex with the highest £ value which obeys Beer’s law for up to 17 /tg/ml of V with an optimum range of 0 3 to 8 /rg/ml. For determi­ nation of vanadium (100 >tg in 15 ml of nitro­ benzene), Al, Ba, Ca, Cd, Ce(IV), Cr(III), Li, Mg, Mn(II) and Zn (in 100-fold amounts) do not interfere; the following are tolerated in the amounts (mg) shown: Ni 1, U(VI) 4, Mo(VI) 0.5, Cu(II) and Co(II) 0.1 and F‘ 4; Fe, EDTA and oxalate interfere seriously. The method has been applied for the determination of V in steel after removal of Fe by extraction.

Diphenylguanidine 405 nm A CHC13 soln. of the reagent is added to a 59 and thiocyanate ions soln. of V(III) in H2SC>4 (pH 1.0) containing acetone and SCN', the mixture is shaken and V is extracted into the organic phase as a ternary complex. Its extinction is measured; Beer’s law is obeyed for 0.7X10"5 to 23X10"4 g-ion/1 of V. Name of the Reagent \nax.or Remarks Refs. working wavelength withe

3-MethyIcatechol 625 nm Dissolve the sample ( = 0.5 g) by heating with 60 40% HF (3 to 4 ml) plus H Q (10 ml) and HgO (15 ml), then heat with HNOa (a few drops) and HgS04 (10 ml) until fumes of SOg are evolved, cool, dilute with HgO, add tartaric acid (2.5 g) and aq. NHg in excess, and dilute to 250 ml. To a portion of this soln. containing = 120 fig of V and HgO (40 ml) and acidified with HgS04, add NagS20 4 (1 g), digest the mixture for 10 to 15 min and cool. Add KCN (0.65 g) and NaOH to pH > 12, heat at = 90’ for 1 h., cool, add tartaric acid to give a final concn. of 30%, add reagent (2.5 g), adjust the pH to 7 with H^S04, dilute to 50 ml and mea­ sure the extinction against HzO. Interference from Mo is minimised. The method is preferred to two other methods where Fe and other metals are removed from the sample solution by electrolysis o r by masking.

Triphenyl methane dyes 450 nm Method describes spectrophotometric determ- 61 «=1530 ¡nation of vanadate, chromate and tungstate. To 5 mi of sample soln. (containing 4.g. 10 ppm of VOg", 5 ppm of CrO^2' or 15 ppm of WO^2 ) was added 1 ml of a mM soin, of crystal violet (C l. Basic Violet 3) in 0.5M- H2S 0 4 and the vol. was adjusted to 10 ml with 0.5M-H SO . After colour development, the requisite time, wave length and e value were, for VOg\ 7 h, 450 nm and 1530, for C r0 42' 2 h, 455 nm and 3140 and for W O ^ 30 min, 630 nm and 1060. In WO for colour establish­ ment M-K2S04 was added. Simultaneous de­ termination of all three was possible. Determination of 2.6 to 22 ppm of VOg , 1.6 to 20 ppm of C r0 42" and 10 to 108 ppm of W 0 42 is possible.

Eriochrome Fed B = 520 nm 4.5 At pH 4.5 medium, V(IV) forms a ternary [C L mordant red 7] complex with both reagents and can be and extracted into CHC13 - isoamyl alcohol (3:1), Diphenyl guanidine and V(TV) in the extract can be determined spectrophotometrically. Vanadium (IV) is separated from V(III), which remains in the aq. phase, where its extinction is determined with sulphonitrazo [8-hydroxy-7-(2-hydroxy-5- nitro-3-sulphophenylazo) naphthalene-1, 6- disulphonic acid] after oxidation to V(V) with ■ u» (NH4)2S2Oa and reduction of this species to V(IV) with ascorbic acid. OJ CN Name of the Reagent PH Remarks Refs.

working wavelength withe

N-Phenylbenzo- 440 nm The water insoluble, red-brown or purple-red 63 hydroxamic acid complex formed by Fe(III) or V(V), respec­ tively, with this reagent was extracted into molten naphthalene. After cooling, the solid naphthalene phase was dissolved in dimethyl- formamide to give a soin, in which 12 to 220/¿g of V or 5 to 100 fig of Fe (at 437 nm) could be determined. Optimum conditions are dis­ cussed.

N-Hydroxy-N-o- 440 nm 4.2 to PentavalentV forms with this reagent a violet 64 tolysuccinamic e=3700 4.9 complex at acidities > IN and an orange com­ acid plex in the pH range 2.5 to 55. The orange complex is extractable into isoamyl alcohol from phosphate buffer medium (pH 4.2 to 4.9) for spectrophotometry. Beer’s law is obeyed for 1 to 10 /¿g/ml of V. A five-fold molar amount of Fe(III) [relative to V(V)] (phos­ phate acting as masking agent) and two-fold amount of A1 are tolerated. EDTA interferes seriously. Salicylohydroxamic 480 nm 3 The sample (e.g. geological material) is fused acid Na CO., an aq. extract of the cooled melt is acidified with dil. H2S 0 4- An aliquot of this soln. is adjusted to pH 3.0 with monochloro- acetate buffer soln. and ethanolic 1% reagent is added. The coloured complex is extracted into isobutyl ketone and extinction is measured. Fe and Ti and removed in the disso­ lution stages. Results agree with certified values.

S'^'-Dichloro-Z- 400 nm 25 to At pH 25 to 4.0 in 75% ethanol V(V) forms hydroxy acetophenone 4.0 yellow (1:2) complexes with each of these re­ oxime (I) agents, the absorbance of each complex is and 5'-ChIoro-2'- measured at 400 nm. Beer’s law is obeyed for hydroxy-4'-methyl 400 nm 5.1 to 35.7 ppm of V with (I) and 5.1 to 30 acetophenone oxime (II) ppm of V with (II).

CDTA[ 1,2-Diamino- 595 nm In the pH range 3 to 9, the blue (1:1) complex cyclohexane-NNN'N'- is formed. For the determination of VO , tetra acetic acid] the test soln. and the reagent soln. are mixed; the pH is adjusted to the desired value. For the determination of V(V), the test soln. (contain­ ing * 60 mg of V and 0.1 to 0.5N in HgS 04) is boiled for 5 min. with a 2 to 3-fold excess of reagent (which acts both as reducing r.nd com- plexing agent). The pH is adjusted to 5 with NaOH and the mixture diluted to 25 ml and then extinction is measured. U 0 0 Name of the Reagent ^max.o r pH Remaries Refs. working wavelength withe

6-Hydroxy-5-axodibenzo 630 n o 4.0 The complex formed between V(V) and cited 68 [a j] phenoatazine-8, compounds can be used to determine 9 to 90 11-disulphonic acid acti­ ofV. To the test soln. are added 10 ml of vated by hexadecyltri- oM dye, 2-5 ml of acetate buffer of pH 4.0 and methyl ammonium bromide 15 ml of 4 mM-hexadecyltrimethyl ammonium bromide, the mixture is diluted to 50 ml with HaO and absorbance is measured against HgO. The Sandell sensitivity is 2.6 ng cm’2. Fe(UI), Fe(II), Mo(VI), Th, Zr(IV), W(VI), Sb(III), Ti(IV), Pb(II), Sn(IV) and Cr(VI) interfere.

W O /an d P O ^ S40nm V(IV) forms red-violet hetropoly anions with 69 W O * ” and TO* in an aq. medium 0.25M in H3P04, 025M in H2SC>4 and 0.08M in Na WO,; the reaction mixture was heated at 100 for 10 min. and then its absorption was measured. Beer’s law is obeyed for 0.5 to 6 /tg/ml of V(IV); 5-fold amounts of V(V), Fe(III) o r Cr(IlI) do not interfere. To determine V(IV) in a V(IV)-V(V) catalyst, the sample (0.2 g) is decomposed by hot 40% H3P04 (10 ml) and concn. HF (3 ml), and absorbance is measured. Benzohydrazide (I) 410 nm 0.5 M- The reagent (1) forms a 1:1:1 VOa+ - 1 - 70 e=5500 HP042 complex with V(V) in a medium — H 3P ° 4 0.5M in H3P 0 4 and 0.2M in L Beer’s law is obeyed for 0.01 to 0.1 mM-V. Cobalt, Fe(III),' Cu(II), Ni, Nb, Ta, Ti(IV), Cr(III), Mo(VI) and W(VI) do not interfere. The method has been used for determining = 0.3 to 2.4% of V in alley steel also containing < 0.3% Mn, < 1% Si, 4 to % Cr, < 0.08% Cu, 0.2 to 3% Ni, < 13% Mo and < 10% W. The coeff. of variation was < 10% (5 results).

Antbranilic add 440 nm 1M to The reagent (I) forms a 1:1:2:1 V 0 3+-I-HS03‘ 71 benzohydrazide €=5200 4M- (or Q ’ or N 0 3")-acetone complex with V(V) in aq. 60 to 80% acetone. At optimum pH, H aS ° 4 or absorption is measured in the presence of 1.5 to 3.5 H SO , and colour is stable for 50 min. at M -H Q or least. A 40-fold molar excess of I relative to HNO_ V(V) is needed. Beer’s law is obeyed for 0.08 3 to 8 fj-g/ml of V(V); no interference is caused by. V(IV), Cu(II), Ca, Nb(V), Ta(V), Mo(VI), W(VI), Os(VIII), Mn(ll), Pd(II), Pd(IV), Pt(IV) or small amounts of Mn(VlI) and Fe(III) can be masked by H3P04, but strong oxidants (C103> I03", Br03’, CrO ^ and U> H O p interfere. Method used for determining VO 0.01 to 10% of V in steel. The coeff. of variation was 2% (6 results) for 1.04% of V in steel also containing 14% and 3.4% Cr. Name of the Reagent X or Remarks Rets. m ax. working wavelength withc

Sulphonitrazo 580 nm V(IV) forms a complex with this reagent in an 72 [8-hydroxy-7-(2- aq. citrate buffer of pH 2.2 to 2.4. The reaction hydroxy-5-nitro-3- mixture containing 0.005% of reagent is sulphophenylazo) heated on water bath for 10 min. at 100*. naphthalene-1,6- Beef’s law is obeyed for 0.2 to 1 jig/ml of disulphonic acid] V(IV). Bivalent Fe, Mg, Zn, Ni, Cd, Mn, (known as Cr(III), Mo(IV), W(VQ, AI(III), Co(lI), sulphonitrazo E) Nb(V) and Zr(IV) do not interfere. The method has been used for determining 0.05 and 1.26% of V in alloyed steels and re- ractory nickel alloys without separating the other components (Fe, Mn, Cr, Ni, Mo, Co, W and Nb; 1 to 13% of each). The coeffi. of vari­ ation was <4.8% (5 results).

1-10-Phenanthroline 450 tun Pentavalent V forms a 1:2:2 [Vo(OH)2+ - 73 and catechol violet e—17200 catechol violet-pbenanthroline] complex, which can be extracted from aq. medium of pH Z4 to 3.4 (Ha-glycine-buffer) into butanol. Absorption of the extract is measured. Beer’s law is obeyed for 0.5 to 4 /tg/ml of V at the optimum wave length of 540 nm; 15-fold and 30- fold molar amounts, respectively of catechol violet and phenanthroline (relative to V) are needed. The following elements are tolerated (amounts relative to V): Re(VII) (2), Ba (20), Ca (25), Sr (30), A1 (10), Mg (40), Cu (5) and Co (5); Fe, Ni, Mo(VI), W(VI), Nb, Ta, and V(IV) interfere. The method has been used for determining = 17 to 56% V in its alloys with AL Coe if. of variation was < 13%. p-Phenetidine with 490 nm 5M-HC1 The sample was dissolved in 5M-HC1 and V 74 BrO * was determined by catalytic oxidation of cited 3 reagent with BrC>3’. The detection limit for V was 50 ppb, and the method was applied to crude oil reforming fractions and gasoline.

Oxalic acid 270 nm 3.0 to 4.2 Tervalent Ti and V(III) form (1:1) complexes 75 with oxalate at pH 1.1 to 2.1 for Ti(III), or 3 to 4.2 for V(III). Max. absorption for Ti(lII) is at 400 nm. Beer’s law is obeyed for oo 0.1 to 13 mM - H(III) or V(II1). To determine Ti(III) and V(III) in presence of each other, the absorbance of a test soln. of pH 1.2 (made 10 mM in oxalic acid and acidified with H Q ) is measured at 400 nm and at 320 nm respective­ ly. The method has been used to determine 1 to 5% of V(III) and 10 to 20% of Ti(III) in Ti- V alloys. The coeft of variation were < 23% (7 results). Up to 60 jug/ml of Fe(ll) and 1 mg/ml of Ti(IV) can be tolerated, but V(1V) interferes, so the analysis must be carried out in an O-free atmosphere. Name of (he Reagent Remarks Refs. Xm ax. or PH working wavelength with e bis-(2-Aminophenyl)- 520 nm 1-2M V(V) forms a reddish violet complex with 76 disulphide HgS04 named reagent (1% soln. in ethanol) in a medium of 1-2M HgS 0 4 o r H Q Absorption of the complex is measured and Beer’s law is obeyed for 15 to 50 pgm of V. The Sandell sensitivity is 27 ng cm' . Tolerance levels are reported for Bi(III), Cd, Gr(III), Be, Zr, Th, U(V), Zn, Ni, Mn(II), W(VI), Cl', B r, BJ)* and NOg. Interference by Pd, Ca, Ba and Sr can be prevented using H Q medium.

N-Phenyl benzo- 530 nm 5 to 9M- At pH of 5 to 9M-HQ.V forms a complex 77 hydrtnamic add HQ with the reagent which is extractable into CHO , and absorbance of the extract is 3 measured. The sample was initially dissolved in HaS 0 4 (concn. < 14%), Na2S 04 or KgS 04 had no effect on colour intensity. Method used for determining vanadium in iron ore, bauxite, ilmenite, beneficiated ilmenite, rutile, and leucoxene. Results were satisfactory for ores containing 0.02 to 28% of V2Og and agreed well with the conventional methods. Isoniazid and acetone 420 nm 2.3 to 3.0 Method used for determination of V(V) in 78 isonicotinohydrazone iron-vanadium alloys and iron ore. The re­ agents form (1:1) red-brown complexes at pH 2 3 to 3 with V(V). Beer’s law is obeyed for 0.2 to 4.0 fig m l1 of V(V) in the final soln. In the presence of Fe, NaF is added and the absorb­ ance is measured at 435 nm. Cu(II), Sb, Bi and Hg(II) interfere.

3-Nitro-N-m-TolyI 540 nm 53 to In a medium 5 3 to 8.5M in HC1, the reagent 79 benzohydroxamic 8.5M forms a complex with V(V) extractable into acid HQ CHClg. The optimum analytical range is 1 to 14 ppm of V, and Sandell sensitivity is 13 ng c m . The method has been applied in the analysis of steel. Further details are given in the next entry.

6to8M To determine vanadium (V) without interfer- 80 HQ ence from Ti(IV), the test soln. was made 6 to 8 M in HCI & 0.1M in oxalate and in citrate (to mask Ti, Zr and Mo(VI)) and shaken with 0.1% soln. of the reagent in CHClg and ab­ sorbance of the extract (dried over Na2SC>4) was measured. Beer’s law is obeyed for 1 to 15 ppm of V. In the determination of 10 ppm of V no interference is caused by 70 ppm of U(VI), Fe(III), Cr(III), or W(VI), 80 ppm of Cu(II), Cd, Zn, Mn(II), Co, Ni, Sb(III), In or Th, or 100 ppm of Ag, Be, Mg, Ca, Sr, Ba, Hg(II), Pb(II), Ga, La, or As(III). Name of the Reagent or Remarks Refs. Xm ax. PH working wavelength w ithe

3-(4,5-Dimethyl-2- 580 nm 5.2 Reagent forms (1:1) complexes with both 81 thiazolylazo)-2-methyl V(IV) and V(V), the former complex being resorcinol readily oxidised to the latter. The sample (0.5 to lg) is dissolved in HQ-HNOg, evaporated to dryness, the residue is dissolved in 6M-HC1, diluted to 500 ml with the same add and Fe extracted from 25 ml of this soln. with a 30 ml portion of isopropyl ether. The Fe free aq. layer is evaporated to dryness, the residue is dissolved in HgO (50 ml) and to an aliquot (0.05 to 036 ppm of V) is added methanolic O.lmM-reagent (10 ml) and acetate buffer soln. of pH 5.2 (25 ml); this is diluted to 25 ml with H O and the absorbance is measured 2 after 15 min. against HgO.

N,3-Diphenyi-propiolo 560 nm 4to8M Reagent (0.1% soln.) in CHQa forms a bluish 82 hydroxamic add e5900 HQ violet complex with V(V) in medium 4 to 8 M in HQ. The complex passes into the CHQ3 layer in which its absorbance is measured against CHQ^ Optimum analytical range is 1.75 to 6.05 ppm of V. O f many other species tested, Mo(VI) and W(VI) interfere but Zr does not.

N-Benzyl benzo 510 nm 5M in Urine samples are oxidised by evaporation to hydraxamic acid «=4300 H a dryness, HN03 and the residue is repeatedly evaporated to fumes with HNOg and HgS04. An aq. soln. of the residue is heated on water bath for 30 min. with HNOg to hydrolyse polyphosphates and aq. KM n04 is added in a slight excess to oxidise V to V(V). Blood and soft tissues are treated similarly, but with initial addition of K2S 0 4. A portion of soln. (15 to 100 #tg of V) is diluted to 25 ml, in medium 5 M in H O and 10 ml of 0.1% reagent soln. in CHQ3 (ethanol free) is added. The mixture is shaken for 2 min., the aq. phase is washed with CH03, then the extract plus washing diluted to 25 ml with CHQ3 and absorbance is measured. Beer’s law is obeyed for 0.7 to 12 ppm of V. There is no interference from Fe(III), Co(II), Ni, Cu(II), UOa(II), Ca, Sr, Ba or Ce(IV). When Zr(IV), Mo(VI), Ti(IV) or W(VI) is present, the extraction of V must be repeated with several portions of 03% reagent soln. o» Name of the Reagent \nax. ** pH Remarks Refs. working wavelength withe

Nitrilotriacetic add 815 nm 3.6 to 4.8 The method involves formation of a 1:1 84 VOZ+-reagent complex at pH 3.6 to 4.8 followed by measuring the absorbance. The analytical range (rectilinear calibration graph) is 1 to 32 mM-V(IV). Tervalent Fe, Mn(Il), Cr(III), N03', O', Br, I', SCN\ SO* and SOg2" are tolerated, but Fe(II), Co, Ni, Cu(irj, CrO.2", NO * and large amounts of PC) , S20 3 , oxalate, acetate and tartrate interfere and must be removed initially. Any V(V) must be reduced to V(IV) with aq. Na2S2Og.

N-3-Chlorophenyl 540 nm 4to7M Reagent (as 0.1% soln. in CHCip is used as 85 dnnamohydroxamic «=5750 HQ extractant for V(V) from a medium 4 to 7M add HCL, and absorbance of the extract is meas­ ured. Beer’s law is obeyed for 0.88 to 7.1 /tg/ml of V. Zirconium, W(VI) and Mo(VI) interfere, 200-fold amounts (relative to V) of Cu(II), Ag, Be, Mg, Ca, Sn, Ba, Al, Ce(IV), Ti(IV), Cr(III), Mn(II), Fe(III), Co(II), Ni(in, U(VI), Pb(II), Cd, As(III), Hg(II), F', B40 72‘, CIO/, oxalate, dtrate and tartrate do not. Acid chrome blue K [C.I., - 3 to 5 Reagems I and II are recommended for deter- 86 Mordant blue 31(1)] (I) mination of V in products of the aluminium blue Sulphonazo {bis[3-(8- magnesium industry. The sensitivities for de­ amino-l-hydroxy-3,6- termining V(IV) are 3.2 ng/ml for I and 4 ng/ disulpho-2-naphthylazo)- ml for II. Beer’s law is obeyed for V concn. up 4-hydroxyphenyl] to 0.5 and 0.6 /¿g/ml respectively. Sulphone} (II)

Benzoic acid 410 nm 1.5 to Reagent forms a 1:2 complex with V in HgO- 87 Salicylhydrazide e=5700 2.5 acetone (3:2) at pH 15 to 2.5 (adjusted with H2S04) and absorbance of the complex is measured. Beer’s law is obeyed for 0.1 to 10 /¿g/ml of V (a 20-fold molar excess of reagent relative to V is needed. > 5-fold amounts (relative to V) of Fe(III), Mo(VI), or W(VI) and an equivalent amount of Cu(II) or Ti(IV) interfere. The complex can be extracted into CHQ3, toluene or ketones.

Ethopropazine 510 nm 5.5 to The red complex is formed with V(V) in 5.5 to 88 hydrochloride 7.5M 75M -H PO medium, an 11-fold excess of the 3 4 reagent for full development of colour is H 3P ° 4 required. Beer’s law is obeyed for 0.1 to 6.0 /¿g/ml of V(V); the Sandell sensitivity is 7 ng/cm . Tolerance limits for 23 cations and 13 anions are given for determination of 2 /¿g/ml of V(V). Fe(M) is tolerated up to 10,000 /¿g/ml. Results obtained for analysis of three steels containing 0.09 to 0.19% of V are in good agreement with certified values. •e» 0 0 Name of the Reagent X or Remarks Refe. m ax. PH working wavelength withe

Diethazine SIS nm 3.5 to The steel sample (0.5 g) is dissolved in 15 ml 89 hydrochloride e=9700 6.0M- of 10N-H2SO4, 2 ml of syrupy H3PC>4 and 1 ml of concn. HNOa- The mixture is boiled for * ¥ ° 4 2 to 4 min., cooled and diluted to SO ml, and 0.1N-KmnO4 is added until a pink colour persists. After S min. the soln. is decolorized with O.OlN-oxalic acid and diluted to 100 mL To an aliquot (3.75 to 165 /¿g of V) are added sufficient tartrate soln. to give a final concn. of 800/ig/ml, 10 ml of 10M-HgPO4 (adjusting the pH to 3.5 to 6.0) and 2 ml of aq. 0.1% reagent soln. The red complex soln. is then diluted to 25 ml and absorbance is measured against a reagent blank. Beer’s law is obeyed for 0.15 to 6.6 ¿ig/ml of V (optimum range 0.52 to 5.0 /tg/mlh and the Sandell sensitivity is 53 ng/cm . Up to 3000 ppm of Fe(III) can be tolerated in the presence of H3PC>4 and added tartrate but Fe(ll), Cr(VI) and Ge(IV) interfere at all concn. Tolerance limits are specified for 33 other species. For determi­ nation of 75 g of V in 25 ml of soln. the error was ± 2% (10 results). S’-Chkwo-y- 400 nm 25 to The 1:2 V-reagent complex was extracted from 9 0 hydraxy-4-methyl- «=3150 4.0 ethanolic soln. at pH 25 to 4.0, into CHCt3 and acetophenone oxime the absorbance of the extract was measured. Beer’s law is obeyed for 5.1 to 30.0 ppm of V, the sensitivity was 0.0162 /ig/cm2. The relative error was ± 1.75%.

Sodium N-(0-carbc«y 530 nm 3.6 to Vanadium (V) forms a 1:2 violet complex with 91 benzoyl)-N-m-iolyl 8.4 cited reagent at pH 3.6 to 8.4. Colour is stable for hydraxylamine [sodium 24 hr. Beer’s law is obeyed for up to 25 ppm of N-hydroxy-N-m-tolyl- V(V), the Sandell sensitivity is 624 ng/cm . At pH phthalamate] 5.8, tolerance limits (ppm) in the determination of 1.52 ppm of V(V) are: M n(II) and Zn, 350; alskali and alkaline earth metals, 180; Infill) and Cr(IIl), 90; and Sn(II), Pd and Sb(IlI), 60. Tetvalent Fe, H(IV), Mo(VI) and U(VI) interfere seriously.

1- (2-Hydroxy-5- 550 nm 29 The cited reagent forms 1:1 complexes with V(V) 92 nitrophenylazo)- e=10,700V(V) and V(IV) at pH 2.9, that are soluble in acetone- 2- naphthoI and HaO(ll:14). The method was used for spectro- •=14,800V(IV) photometric determination o f 2.5 to 80 ¿¿g of V in 25 ml of final soln.; interference is caused by >500 fig of As, >200 fig of Mo, Co, Cu, W or U, >100 fig of Zr, Ce, Cr, or Si and >10 fig of Fe. By extraction of the V(V) complex from the reaction mixture at pH 0.75 into CHC13, 0.1 to 35 /xg of V can be determined without interference from, e.g., Zn, Mn, AI, Pb, U, W, Ce, PO3^ or silicate; Mo, Co, Cu, Zr, Fe and V(IV) interfere. Refs. to9Mand in HC1 then shaken with to 10 ml 15 fordetermination of Ti(V) and V(V) by Remarks Thetest soin. to[20 200//.g ofV(V)] madeis 3 ofa 0.1% reagent soin, in CHClg. The 93 CHCI3 spectrophotometry of their 1:1 complexes. To reagent in the case ofH and 4 ml of 8x10 M extract (violet) is dried over Na2S04 and the reagent soin., and then with CHQgportions) (3 to 4 ml until no colour is remaining. made The up tomeasured. 25Beer’s law is mlobeyed. has The before method been absorbance applied is for determination of an aliquot [1.5 ppm ofV(V)] Ti(IV))was addedor 6 1x10 ppm M of alcoholic soin, ofin the case ofThe V.- pHadjusted of to4.5 withthe acetate mixturebuffer, was thesolution aq. phase isagain shaken with 2 to 5 ml ofthe Thecited compound isproposed asa reagent 94 wasdiluted to 25 ml and absorbance measuredagainst corresponding reagent blanks; for washings are combined with the extracts and vanadium(V) steel in (0.24% and 0.46%). 3to9M HC1 4.5 630nm withe 590nm working wavelength «=5500 «=3500 phenone N-(4-Chorophenyl)- 2-thenohydroxamic acid Nameofthe Reagent \nax.or pH 4'-trihydroxyaceto­ 5',6,-Dibromo-2'3’,

50 Ti(IV) absorbance was measured at 390 nm (e=J7,500), Beer’s law is obeyed in the range of 0.15 to 2 ppm for Ti(IV) and 0.5 to 8 ppm for V(V). There is no interference from Cu, Ni, Co(II), Zn, Cd, Hg(II), Mn(II), Cf, Br\ or I*, but serious interference from U(VI), Th(V), Zr(IV) and Fe(II).

3-3'-Dimethyl 555 nm 8M- A finely ground sample of 0.5 g is fused with naphthidine 10 g of NaHS04, the cool melt is leached with H 3P 0 4 disulphonic acid 50 ml of hot 2M-H2SC>4 and the filtered soln. is diluted to 250 ml. To a 25 ml aliquot are added a few drops of 0.1M-KMnO4 to give a permanent pink colour [indicating oxidation of V(IV) to V(V)]. After 5 min. the soln. is wanned, treated with 5 mM-oxalic acid until the pink colour just disappears and diluted to 100 ml. An aliquot is treated with 1 ml of 0.1% reagent soln. and diluted to 25 ml, sufficient 12M-HgP 0 4 is added to give a final acid concn. of 8M, and after mixing the absorbance is measured. NOa*, I’ and Ag+ interfere seriously. The method has been applied to determination of vanadium in steels and ilmenites. Ul M Käme of the Reagent pH Remarles Refs. Xmax. or working wavelength withe

4-Methyl- 600 nm 5to7 To an aliquot containing 0.8 to 1.6/¿g oi V(V) daphnetin «-=900 and 10 to 25 /tg of UOg2+ are added 0.1M alco­ holic soln. of reagent and pH of the soln. is adjusted between 5 to 7. The resulting soln. is diluted to 25 ml and absorbances are measured against their corresponding reagent blanks. With U(IV) the reagent forms an orange yellow complex which exhibits max. absorbance at 450 nm (c = 2700) and with V(V) a bluish green complex. Mo, Fe, Ti and W interfere. The method has been used for simultaneous determination of V(V) and U(VI).

Toluene, Cyclo- 550 nm Petroleum residues were dissolved in the solvents hexane or Pyridine cited and absorbance of soln. was measured. Beer’s law is obeyed for 0 3 to 3% (w/w) of residue. The graph of absorbance vs. concn. of V in the range 43 to 46 ppm was slightly curvilinear for samples of the hydrogenated residue in any of the solvents cited and for the undissolved samples. Specific correlation had to be made for each feed stock. Diphenylamine 560 nm >0JM Vanadium (V) and Cr(VI) were detected as pink 98 in spot (at room temp.)> with 0.1 mM reagent soln. in HaS 04 presence of Fe(CN)3"6 (0.1 mM) and >0.5 M H9S 0 4. The limit of detection was 0.2 /ig for V and 0.017 /ig for Cr. Both were showing the same absorbance and so have been used for determination of V and Cr. Beer’s law was obeyed for 0.5 to 3.0 ppm o f V and 0.17 to 1.0 ppm of Cr. Error was ± L5%, Nitrate, CI04‘, SO^’, acetate and citrate did not interfere, but S , NOa", tungstate, molybdate and coloured ions including Fe and Co did.

Catechol violet 655 nm 4.8 In the soln. of pH 4.8, V(IV) forms three com- 99 0 ) «=9500 plexes (ZT:2,1:1:2 and 1:2:3) with (I) and (II), Diphenylguanidine extractable into pentanol or pentanol-CHCl3 (1:1) (I) for determination at between 650 to 600. The last complex (1:2:3) is the most suitable for the analytical purpose. Tervalent V is oxidised by (I) to V(IV). Up to 1 fim - V(V) has no effect, and 100- fold amounts (relative to V(1V) of Cu, Zn, Ca, F- o r ? 0 * , 1000-fold amounts of Mg, Cr(III) (if masked with ascorbic acid), 10-fold amounts of Fe(III) do not interfere, oxalic, tartaric, citric acid, IA EDTA and A1 interfere. Name of the Reagent X or pH Remarks Refs. m ax. working wavelength withe

4-Methaxy-N-m-tolyl 530 nm 4 to 8 Determination of trace vanadium (V) in soil and 100 benzohydraxamic acid M-HCI steel is studied. Sod (1 g) is fused with 5 g of Na2COa in a platinum crucible, the melt is leached with 30 ml of HzO, the soln. is filtered and diluted to 50 ml. A steel sample containing — 1 mg of V is heated with 210 to 12 ml of 3M-H2S04 until reaction ceases. Cone. HNO. is then added, 3 further heated and the soln. is filtered and diluted to 100 ml. For either type of sample, an aliquot containing 15 to 20 ¿tg of V(V) is mixed with a little KMnC>4 soln. and sufficient aqueous H O (4 to 8 M), 5 ml of 0.1% reagent soln. in CHC13 are added with shaking for 2 min., the CHClg phase dried over Na2S 0 4. The aq. phase is shaken again with 1 ml of reagent soln. The organic phases are combined with 1 to 2 ml of CHC13 before measurement against CHCI3. Beer's law is obeyed with 1 to 7 ppm of V. Trace amounts of Zr and Mo(VI) are tolerated. Errors ranged from -1.0 to + 05% (relative) for soil and from -0.01 to +0.025% (absolute) for steel containing 0.46 to 157% of V. N-Allyl-N,(p- 360 nm 10M-HC3 A portion of soln. (60/tM in 10M HCI) was attrac- benzoylglycine)- and ted with a soln. of reagent in isoamyl alcohol, and thiourea[4-(3-allyI- e -1900 at then with pure isoamyt alcohol, and the absorbanc- 2-thioureido) bippuric 380 un ces of the combined extracts were measured. The add] ratio was 1:4. Beer's law was obeyed for 1 to 22 ppm of V(V) and the Sandell sensitivity was 0.048 ¿ig/cm2. A stable 1:3 complex was formed at pH7 to 9.5 M. Various ions commonly assodated with V did not interfere, but Hg(II), Cu(II), Ni, Co, Fe(III), H(IV) and U(VI) did.

N’-Hydraxy-N2 575 nm • The sample soln. is mixed with anhyd. acetic add phenyl-N'-p-tolyl- (10 ml), diluted to 25 ml with H O, then extracted benzamidine with two 5 ml portions of a 0.1% soln. of reagent in CHQ . The organic phase is dried over anhyd. NaaS04 and made up to 25 ml CHC13 and the absorbance of the blue violet V(V)-reagent complex is measured against CHC13> The optimum analytical range Is Z 0 to 8.5 ppm of V, for which the calibration graph is rectilinear. Serious inter­ ference is from W(VI) and Ti(IV).

Thiocyanate and 340 nm 0.42 to The ternary complex formed between V(IV) and diphenyl e =»170000 to2£N dted reagents at ratio (1:2:2) is extractable into guanidine HCI, 1.8 CHClg. Absorption of aq. phase is measured after to Z 7 N reextraction. Beer's law is obeyed for 1 to 100 ¡x% of h 2s o 4 V in 15 ml of the aq. phase. Interference from Fe(III), Cu, Mo, Nb, and Ta can be eliminated. o \ Name of the Reagent X or pH Remarks R e f is . m ax. working wavelength withe

2,-4'-Dihydroxy- 400 nm 2 to 4.1 Colorimetric studies on the reaction of di- 104 valerophenone oxime oxouranium (VI), dioxomolybdenum (VI) and oxovanadium (V) have been made. The species UO +, MoOa + and VOa+ form with the reagent (HgL) orange yellow complexes of the type MC>2 (HaL)2 (M = Mo or U) and VO(OH) (H3L)2- Hie U, M o and V complexes have the same absorption max. in the pH ranges 3.0 to 5.0,2.0 to 3.5 and 2 to 4.1, respectively. Beer’s law is obeyed in the respective concn. ranges of 4 to 90,2 to 20 and 8 to 120 ppm.

N'-(5 -Chloro-o-tolyl)- 595 to 2 to 3.5 In the presence of phenols 1:2:1 (V-I-phenol) com- 105 N-hydroxy-N-(m-tolyl)- to 600 nm plexes which are extractable into CHC13 are p-toluamidine- formed. Such reactions involving phenol, 4-chloro- hydrochloride (I) phenol, o-m- and p-cresol and 2-naphthol can be and various phenols used for determination of jug amounts of V at pH 2.0 to 3.5 phthalate, Cl', Br, I03*, N 03", SO*, NH^+, alkali and alkaline-earth metals and lanthanoids do not interfere, up to 350-fold amounts (W/W) relative to V. Tetravelent Fe can be masked with NagPO^; W(VI) interferes and must be removed initially. The method is used to determine V in steels.

Lumogallion IREA 520 nm This method for determination of vanadium in 106 [5-Chloro-3-(2,4- «=32,000 natural water involves extraction with a 05% of 8- dihydraxyphenylazo)- bydroxy quinoline in CHC13 at pH 3, back extrac­ 2-hydraxy-benzne) tion with an NH4N 03-based buffer soln. of pH 9.4 sulphonic acid and oxidation with HQ-HG)3. The soln. is evaporated and the residue is dissolved in HzO; citric add is added to mask A1 at pH 8.9, and a 0.02% soln. of reagent is added to form a coloured complex with V, for which absorption was measured in presence of 30% of acetone. The sensitivity is 0.02 mg/1 with error of <4%.

Picolinic acid 385 Dm The neutral sample soln. is mixed with neutralised 107 aq. 8% of reagent (4 ml) and diluted to 20 ml with HgO, then 0.7 to 2 g of N a^C ^ is added. The mixture is shaken for 1 min. and extracted with CHC13 (2x10 ml and 5 ml). The extracts are filtered, combined and diluted to 25 mi with CHCla and absorbance is measured against a reagent blank. V(V) is reduced by the N a ^ O ^ to V(III), which forms the complex. Beer’s law is obeyed for 1 to 50 ftg/ml of V. Phosphate, F , oxalate, thiourea and EDTA should be absent. There is no interference from any other metals. Further interferences can be masked. L* 00 Name of the Reagent X or pH Remarks Refs. working wavelength with«

i) N -(4-ChlorophenyI)- 615 nm 2 Dilute the sample sola, to 25 ml with HzO and ad- 108 N-hydrwty benzamidine, just the pH to 2. Add 10 ml of 0.06M reagent (i, ii, ii) N-hydroxy-N-phenyl 610 nm o r iii) and 5 ml of 0.03M-anisaldehyde, both in benzamidine CHC13 and shake for 2 min. Separate the CHC13 iii) N-Hydraxy-N-p-tolyl 610 nm layer and dry it with Na2SC>4. Extract the aq. soln. N'-(3-chloro-4-methyi- soln. with more CHC13- Dilute the combined ex­ tracts to 25 ml with CHC1 and measure the ab- phenyl)-p-tolumidine 3 and anisaldehyde sorbance. For the respective reagents, the corresponding range over which Beer’s law is obeyed is (ppm) 0.6 to 8.4,1.0 to 8.6 and L2 to 9.0. Tiingstate interferes seriously but interference from Fe(IlI) can be eliminated by masking with NaPO . 2 4

N-Phenyl-1- 545 nm 6 to 8M- This method has been used for simultaneous trace 109 naphthahydraxamic HCI determination of vanadium - uranium - cerium and acid iron in rocks and mineral samples. The sample soln. (10 ml), 6 to 8 M in HC3, is shaken for 5 min. with 0.1M - reagent soln. in ethanol free chloroform (5 ml) and absorbance of the separated organic phase was measured, the calibration graph bang rectilinear for 03 to 9.0 ppm of V. Salicylic acid 410 nm 4to6 Determination of titanium and vanadium by cited 110 2,4-dihydraxy *=12500 reagent is studied. Vanadium (V) forms a (1:1) benzylidene hydrazide complex with the reagent in a medium of aq. 40% acetone (pH 4 to 6) that is 4 mM in reagent This complex also can be extracted into CHCI3 or benzene and absorption of the extracts was measured. Beer’s law is obeyed for 1.2 to 4.8 fig/ml of V(V). Al, Ta and Nb do not interfere. When the method was used to determine 0.6% of V in a prepared soln. (containing Al, Ta, and Nb), the coeft of variation was 3% (5 results. Ti(IV) was determined at pH 0.6 to 1.8 (400 nm, e = 24000) with this reagent

N-Phenyl acetyl 640 nm 6to8 To the test soln. (0.02 to 0.2/rg of V) are added 111 mandelohydraxamic M-HC1 HC1 (6 to 8M) and HaO to bring the vol. to 25 ml, [2-acetoxy-N, 2- 5 ml of a 0.01M reagent soln. in ethanol free chlor­ diphenylaceto- oform is added, the mixture is shaken for 1 min. A hydraxamic] acid soln. of 2M Guaiacol (5 ml) in chloroform is then with phenols added and the mixture is shaken for 3 min. After separating the aq. layer is washed with chloroform, and the combined organic solns. are made up to 25 ml before measuring the absorbance against a reagent blank. The method has been used to determine 0.5 to L5% of V in steel. Of 35 species studied including Ti(IV) and Zr(rV), only Mo(VI) and W(VI) interfere. c\ O o r pH Remarks Refs. Name of the Reagent Xm ax. working wavelength withe

Sulphochlorophenol 627 nm 3.7 to To the test soln. containing up to 40/ig of V(V) 112 N[3<5-Chloro-2- 6.0 are added 5 ml of 0.1M - acetic acid, 0.1M - Na hydraxy-3-sulphophenyIazo)- acetate (pH 5.0), 1 ml of 0.1M • citric acid and 5 ml 6-(4-nitrophenylazo)J of aq. 0.2% reagent soln. After 10 min. the absorb­ chromotropic arid. ance of a blue complex is measured, which is stable over the pH range 3.7 to 6.0. Cii and Co interfere seriously. The method has been used to determine V in steeL

N1-4-ChIoro- 610 nm 2M- Up to 200/igofV(V) is extracted from 2M-acetic 113 phenyl-N2 -(4- «=6500 Acetic acid soln. containing 0.4% of KSCN or NaN3 into chloro-o-tolyl- acid 25 ml of a 0.1% soln. o f reagent in CHC13 and de­ N 1-hydroxy benza- termined. The ratio of complex is 1:2:2 [metal to midine) hydrochloride reagent to anion (SCN' or Ng )]. Many common with SCN" or with N3" 590 nm ions do not interfere. The method has been applied «=6500 to standard steel samples.

N1 -(4-chlorophenyl)- 580 nm Acidic To the aq. soln. ofV are added a carixsylic acid 114 N2-(5-chloro-o-tolyl)- f=4700 medium and a soln. of the reagent in a solvent and the ab­ N-hydroxy-p-toIuamidine sorbance of the separated organic layer containing hydrochloride and various the ternary complex is measured. When the acid monobasic carboxylic acids and solvent are acetic acid and CHC13 respectively, Beer’s law is obeyed for 1 to 9.5 ppm of V.

Fe(UI) ofV(V), 2 ppm of ppm 1:1 H1:1 Qand filtrate evaporatedis to dryness. A few Steelsample (containing2.5V)of mg dissolved is 116 maketo To250the voL mL an aliquot are added 10 CHC3; the absorbance of the blue violet (1:2) in2040%of ml HNOg. Tungstic acid pptd. is with mlof aceticadd to give a7M soln. and H O upto respectively(10 results). drops of 1% HNOg are added and then HaO to 25 ml; the mixture is extracted with soln.0.1% in reagentCHOg (4x3 ml) and diluted to25 ml with interfere. and 8 ppm of Mo(V), presentof together, variationthe coeff. were ±0.6%, ±05% and ±0.8% Mo(V). Tolerance levels were tested. For complex is measured. Iron, Mo and H do not 4.8for Fe(III);to 1.2 6.8 forV(V) and2.8 to for14 determination of4 Determinationofiron(in),vanadium(V) and mol- 115 («=4xl03) for Mo(V) respectively. The complexes 0.2to 0.8M - H Q and thatof Mo(V) in 3.5M-HQ.The optimum analytical ranges (ppm) are 0.8 to reagentSCN")complex with Fe(III) and with1:2:2 ybdenum(V) asmixed complexes described.is In aq.SCN medium,the reagent forms a (metal: 1:1:2 both V(V) and Mo(V);nm the («»1.12X104) complexes for are Fe(III) and 470 nm extractable into benzene for measurements at 460 with Fe(III) and V(V) are formed in a medium of acid 7M- nm 1 -(4-chlorophenyl)- 1 '-hydracy-N2(23- 610nm «=6800 0.2to 0.8 N2-p-tolylbenzamidine Acetic with thiocyanate N 1-Hydro*y-N1-phenyl 575 z z xylyl)-p-toluamidine M-HQ Name of the Reagent X or pH Remarks R e f it . max. * working wavelength with c

Furoin 0-oxime 349 nm < 0.07 At pH < 0.07 a 1:1 yellow-brown complex is 117 formed between V(V) and cited reagent which is soluble in H2<3 and insoluble in benzene, CCI4 and CHQ3. V can be determined between 1 to 7 /Ig/ml by measuring the absorbance.

Picolinaldehyde 425 nm 2.1 The reagent soim, 0.1% in ethanol, forms with 118 salicylohydrazone & 400nm V(V) at pH 2.7 a yellow complex, extractable into chlorobenzene for measurements. Alternatively measurements may be made in aq. sola. at 400 nm. The optimum ranges are 1.1 to 1.5 ppm by direct method and 0.3 to 1.75 ppm with extraction. This method has been used to determine V in steel and in lead concentrates.

Dithizoneand 503 nm »4 Equal volumes of aq. — 0.1 #tM-V(V) of pH = 4 119 tributyl phosphine and of benzene containing 039 /iM-dithizone and oxide (TBPO) 0.1M TBPO were shaken together for 10 min. The resulting red complex in the benzene phase was stable for at least one hr. and its absorption measured. In the absence of dithizone, no extraction of V(V) occurred. Promethazine 5.17 nm Vanadium (V) forms a complex with a 16-fold mol- 120 hydrochloride <•=9600 ar excess of the cited reagent. Beer’s law is obeyed for 0.1 to 7.0 ppm of V(V); the optimum concn. range is 0.5 to 7.0 ppm and Sandeli sensitivity is 5 ng/cm . In the determination of 2 ppm of V, up to 3000 ppm of Fe(III) is tolerated in the presence of HgP04 and citrate. This method has been applied for determination of V in steel

N-Phenyl benzo- 530 nm Determination of V in stainless steel and nickel 121 hydraxamic acid base alloys with cited reagent is studied. A sample (0.5 g) is heated with 20 ml of aqua regia then with 5 ml of HCIO^ and finally heated to fumes after adding 14 ml of H.,S04 (1:1) and 5 ml of H3P 04- The residual soln. is transferred by H?0 to a polyethylene separating funnel 10 ml of 40% H F is added and the soln. diluted to 50 ml with HgO, and 4 ml of 10% (N H V S 0 4. FeS04-6H O soln. is added to reduce Cr(YT). After 2 to 3 min, 10 ml of 45% (NH4)2S2Og soln. is added to oxidise V to V(V) without oxidising 0(111). After a further 5 min. the soln. is shaken for 2 min. with 20 ml of 0.1% soln. of reagent in CHOa and absorbance of the extract is measured against CHCJ^. In determination of 100 ¿ig of V, no interference is caused by 1 g of Fe(IlI) or Ni, 0.5 g of Cr(III), 0.2 g of A l 0.1 g of Mo(VI), 50 mg of Mn, Co(II), Ti(IV) or Nb(V), 20 mg of Si, 10 mg of Cu, or 5 mg of Ta or W(VI). Name of the Reagent X or Remarks Refs. m ax. working . wavelength withe

Hydroxy amidine 590 nm 1 to Vanadium (V) forms a chelate with the cited re- 122 [N1-(4-chIorophenyl)- 10.2 agents in the ratios of 1:2:1. Absorption is meas­ N -(4-chIoio-o-tolyl)- ured in CHClg soln. Beer’s law is obeyed for 0.5 to N2-hydroxy benzamidine] 5.5 ppm of V. Tervalent Fe, Cu(II), Ni(II), Co(II), and 4-hydroxy benzaldehyde Mn(Il), Zn(II), Cd(II), Al, Cr(III), Ti(IV), Zr(IV), Nb(V), Ta(V), Mo(VI) and W(VI) do not inter­ fere.

Methyl trioctyi- 560 nm 5.5 to Determination of small amounts of vanadium from 123’ ammonium chloride 5.6 solns. containing iron (III) is studied. The sample of V with 4-(2-pyridylazo) resorcinol was extracted into an equal volume of 0.1M of reagent soln. in CHC1_ by shaking for 3 min. After extraction at pH 53 to 5.6, V in the organic phase was deter­ mined. By masking Fe(III), present in the same amount as V (1 to 10 /im), with 0.1M - 1,2- diaminocyclohexane-NNN’N' - tetra acetic acid, an average error of ± 4.2% was achieved. Large amounts of Fe could be removed by extraction of its complex with reagent at pH 9 to 10; the pH was then lowered for extraction of V. The average error in this instance was ± 4.4%. N-(4-Qilorophenyt) 545 mn Acidic To a mixture of the test soln. (2 ml), HgO (3 ml) 124 cinnamohydraxamic add and cone. H a (10 ml), 5 ml of a 0.1% soln. of reagent in CHQ3 are added. The CHQ3 layer is dried, then diluted to 25 ml with CHQg, and absorbance of the bluish-violet (1:2) complex is measured. The calibration graph is rectilinear for 0.08 to 9 ppm of V, and sensitivity ¡8 = 8 ppb. The standard deviation was ± 0.02 (eight determina­ tions at each of nine concn. of V between 0.9 and 100 ppm). Mo, Ti and Zr must be masked with NaF. Results are reported for steel, phosphorite, vegetables, water and rodent organs. 2(2-Diethyiamino) 460 to 4.5 to T o the test soln. add 1 ml of 0.01 M antipyrine, 125 ethylamide-benzoate- 480 nm 5 dilute to 10 ml with ammonical acetate buffer of (4-azo-5-)-8-hydroxy- «=31000 pH 4.5 to 5, extract with 10 ml of 0.1 mM soln. of quinoline[N-(2-diethyf- the cited reagent in CHQ ^butanol (4:1) with aminoethyl)-4(8-bydraxy- shaking for 1 min. and measure the absorbance of quinoline-5-ylazo) the organic phase. The absorbance is related recti- benzamide]-antipyrine lineariy to the concn. of V in the range 0.02 to 0.8 /xg/ml. There is no interference from Fe or larjg amounts of alkali or alkaline-earth metals, S2Og or phosphate, but Bi, W, F* and EDTA interfere and the following are tolerated (amount relative to V): Cr£,07a', 44; Cr3+, 56; Ti(IV), 10; Cu2+, 3; Zn2+, 320; Mn , 2200; Fe2+, 2500; A1(III), 80; Cb2+, 59; M o04, 1; Ni2+, 587; thiourea, 800; and dtric acid 570. The method is proposed for determination of V in industrial and biological samples and steels. o Name of the Reagent A . o r pH Remarks Refs.

working wavelength withe

N -p-Tolylbenzo- 445 nm 2 to The test soln. [50 to 100 ¿tg of V(V)] was adjusted 126 hydroxamic acid e=2350 4 to pH 2 to 4,0.2% of reagent soln. in CHQ3 (3 ml) was added and heated to >86\1* and shaken with naphthalene (1 to 2 g). After cooling, the solidified extract was filtered off and dissolved in dimethyl formamide (total voL 25 ml), and the absorbance of this soln. was measured against a reagent blank. Beer’s law was obeyed for 10 to 200jugfml of V(V). There was serious interference from Fe(III), Ti(IV), No3* and UOg2+, whereas 50 ppm of Ni(II), Cd, Mn(II), Cr(VI) or Th; 500 ppm of Zn; 1000 ppm of Mg or Cu(II), 05% of A1 or tartrate and 1% of Pd(II), Cl\ V, SCN', SO*, HP O*, H2P 0 4", or acetate could be tolerated.

N-4-Tolylacetyl- 645 nm 6 to Transfer an aliquot of oxidized soln. containing 127 mandelohydraxamic 8M-HC1 0.02 to 0.2 mg of V(V) to a separatoiy funnel; acid in presence make it 6.0 to 8.0 M in H Q and add H20 up to a of 2-methaxyphenol final vol. of 25 ml. Add 5 ml of reagent soln., shake fora min., add 5 ml of 2.0 M chloroform soln. of o- methaxy phenol and shake the mixture for 3 min. Collect the chloroform layer in a 25 ml flask. Wash the aq. phase twice with 4 ml of chloroform, collect washings in the same flask, dilute with chloroform and measure the absorbance against a reagent blank. Analytical range was 1.7 to 63#rg/inl of V in CHClj soln., and Sandell sensitivity was 8.5 ng/ cm2. Mo(V) and W(VI) interfered. The method has been applied for analysis of steel.

N ’-Hydraxy-N’-N2 610 nm 1.5 The test soln. [30 to 200/rgofV(V)] was added to 128 diphenyl-p-toluamidine 1% KSCN soln. (5 ml) and the mixture was diluted and thiocyanate and adjusted to pH = 1.5 and added to 0.1% soln. of reagent in benzene. The organic phase was separated and dried, and the absorbance was measured against benzene. This procedure was followed for a soln. containing [V(V) (20 to 160 fig)] and [Fe(III) (10 to 100 p.g)[ at pH — 1.2 and absorbance was measured against a reagent blank at 460 nm and 610 nm and composition deter­ mined by solving simultaneous equations.

4-Hydraxy-3-Salicy- 420 nm 5 The sample soln. (up to 100/xgofV) is mixed with 129 lideneamino benzene e = 11400 5 ml of acetate buffer of pH 5 and 5 ml of 0.1% sulphonic acid reagent soln. and the mixture is diluted to 25 ml with HzO. The absorbance of the yellow complex is measured against reagent blank. Beer’s law is obeyed. Aluminium, Cu(II), Fe(III) and Mo(VI) interfere with the determination, but all except Mo can be masked with thiourea or NaF. The method is applied for determination of V in steel (0.1 to ON 03% ) after removing Fe by extraction with ethyl ether from 6N-HC1 medium. o\ oo Name of the Reagent X or pH Remarks Refs. max. woridng wavelength withe

Di-2-pyridyl 550 nm 3.7 To the test soln. [containing 3.8 to 20.4 jug of V 130 [Ketone]2-quinolyl- «=22,800 to (VI)] is added 2 ml of an ethanolic 0.01M soln. of hydrazone 5.9 reagent at pH 3.7 to 5.9, the final vol. is made up to 10 ml with water and ethanol (concn. 50%) and absorbance is measured. Beer’s law is obeyed for up to 2.29 ppm of V, the Sandell sensitivity is 2.2 ng/cm2.. Oxalate, CN", ritrate, EDTA, Co, Fe(II) and Pd(II) interfere seriously.

Salicyiohydroxamic 330 nm 0.5 V(V) is separated from V(IV) by extracting the 131 add h 2s o 4 V(V)-reagent complex from a medium of 0.5M HgS 0 4 into heptanol-CCl4 (3:2); the absorbance of the extract complex is measured. Beer’s law is obeyed for 0-5 to 20 fig/ml of V(V). In the remaining aq. phase V(IV) is oxidised to V(V) by (NH4)2SO and this V(V) is determined in the same way. Tolerable amounts (relative to V) are: Fe(III), Al, Cu, Zn or U(VI), 160; Mg, Ba or Ca, 200; and tartrate, citrate, PC^3", or EDTA, 500. The method has been used for determination of 0.008 to 3.6% of V(V) and 0.16 to 6.7% of V(IV) in glass, bauxite, iron ore and vanadium ores; the coeff. of variation was < 5.8%. 2-(5-Bromo-2-pyridyiazo)- 605 am 4.6 To the test soln. (1 ml) were added 5 ml of 132 -5-dietbylaminophenol acetate buffer soln, of pH 4.6 and 5 ml of a 0.11 (5-bromo-PADAP) o M coin, of the reagent in ethanoL After 3 min, the soln. diluted to 50 ml with H O and its absorbance was measured. Nickel, Ti(IV) and W(VI) interfered, but Fee(III) and Cu(ll) could be masked with NaF and thiourea respectively. Up to 5 y.% of NaCl or KQ did not affect the result. The method has been used to determine VO * in table 3 salt.

N-(2-Methoayphenyl>- 445 nm — 15 V(V) is extracted from 3 to 6M-HC1 with 0.05M(I) 133 2- thenohydraxamic add (I) in CHQ3- After 5 min. the organic layer is separ­ and ated and dried and added to HaO (at pH — 13); 3- (2-carbacy phenyl)- 0.01M (II) in acetone is then added and the result­ 1-phenyl-triazene- ing colour in the CHC13 is measured. The Sandell 1-oxide (II) sensitivity is 5 ng/cm2, and Beer’s law is obeyed up to 20 ¿tg/ml of V. The method has been applied for determination of ferrovanadium alloys and phosphate rock.

N-(2-Chlo(ophenyl) 550 nm 4 to 7 Test soln. (0.02 to 0.2 mng) of V(V) was made 4 to 134 cinnamohydroxamic ad d M-HQ 7M in HQ, then 10 ml of 0.1% soln. of cited reagent in ethanol-free CHQa was added and the complex (stable for 24 hr.) was extracted into CHCla and its absorption measured. Beer’s law is obeyed for 15 to 55 ppm of vanadium. Zr, Ce(TV), Mo(VT) and W(VI) interfere (out of 28 foreign species). This method has been used to determine vanadium in steeL «J o Name of the Reagent or Remarks Refs. working wavelength withe

N-{4-Ch!oropl>enyl)-N A blue ternary complex is formed between V(V), 135 -(3-chIoro-p-tolyi)- reagent (I) and either (II) or (III) in acetic acid N-hydraxy-p-toluamidine (I) medium of up to 6M. The complex is extractable and into CHC13 (25 ml) and absorbance is measured at Phenol, 4-chlorophenol (II) 595 nm 595 nm (with use of phenol or II) or 625 nm (with 2-naphtbol (III) 625 nm use of III). Analytical range between 0.6 and 7 ppm of V, the calibration graph being rectilinear; the Sandell sensitivity is — 7 ng/cm and coeff. of variation is 0.73% for 100 /¿g of V. Ethanolamine, NH3, urea, thiourea, phthalate, alkali and alkaline earth metals and rare earth metals do not inter­ fere; permissible limits (ppm) in the CHC13 extract of metals commonly associated with V(V) range from 75 for Zr to =* 200 for Zn, Al, Ti(III), Bi(III), Ni and Co, provided that W is initially removed as hydrated oxide; a 0.1% soln. of I in CHC13 is used in analysis. The method has been applied for V determination in steels and has advantages over other methods.

N-Phenyi-2- 550 nm The determination of trace V and 11 in petroleum 136 naphthohydraxamic acid crudes has been described. The sample (4 to 10 g) is heated (up to 160°) under an IR lamp until a semi-solid black material is obtained and moistened with concn. HNOg; then heated to dryness with concn. HQ and the process is repeated. The residue is oxidised by fusion with KHSC>4, then heated again with H Q and the re­ sulting soln. is evaporated; the residue is treated with 0.1N-HQ, any carbon particles are filtered off, and V in an aliquot of the filtrate is oxidised by KMN04 to V(V), which is determined by extrac­ tion (in presence of HO and NaF) into CHQg as the complex with cited reagent and absorbance of the complex is measured. A similar method for determining Ti has been described. Vanadium (6 to 8 ppm) can be determined.

-(3-ChIoro-jMotyl)- 590 nm To a soln. containing 100 /tg of V(V) is added an- N -hydraxy-N1 -p-tolyl- and hyd. acetic acid (10 ml); after dilution to 25 ml, 5 toluamidine in presence 625 tun ml each of 15 mM reagent and a0.2M soln. of of various phenols. phenol, both in CHQ3, are added. After 1 min. the organic phase is removed, dried and washed (with C H C y and diluted into a 25 ml flask and absor­ bance is measured at 590 to 625 nm, depending on the phenol used. Beer’s law is obeyed from 0.6 to 9.0 ppm of V(V), and the optimum analytical range is 1.0 to 83 ppm. The coeff. of variation is 0.6 to 0.9% for 4 ppm of V in 25 ml (10 determinations). Up to 1500 ppm of Q ', B r, NO'3, SO*4, N H +4, triethanolamine, urea, thiourea, alkali or alkaline earth metals or lanthanoids do not interfere. K > Name of the Reagent \nax.or pH Remarks Refs. working wavelength withe

2-Methyl-4-(2- 550 nm 4.75 Vanadium forms two complexes with dted reagent 138 thiazolylazo)- *=16,600 A spectrophotometric method which is superior to resorcinol and that of ASTM has been developed, for the deter­ «=27,500 mination (at an optimum pH of 4.75) of 0.2 to 1.63 ppm of V in fuel oil.

Na salt of 6-Hydroxy- 630 nm 2 The dyes used formed ternary complexes of types 139 5-cxo-derivatives of: and to v y v 4, v iy v 6 and v n y v , where the last two Benzo [a] phenaxazine- 615 nm 6.5 sufficiently stable between pH 3 3 to 43. To the 10-sulphonic acid (I) sample soln., containing 5 to 100 /tg of V, and 7 ml and Dibenzo [a j] ml of a 1 mM sola, II or IH, acetate buffer of pH 2 phenoxazine-9,11- (II) to 63 (5 ml), 10 mM-IV (20 ml for II o r 7 ml for o r -11,13-disulphonic III), and make the voL up to 50 ml with HzO. After ad d (III) with 15 min. measure the absorbance at 630 nm (for II) {l-[(ethaxycarbonyl) or 615 nm (for III) against a reagent blank. Up to pentadecyl] trimethyl- 0.1 to 2/tg/ml of V could be determined with coeff. ammonium bromide} of variation of « 0.8% (6 determinations with each (Septonex) (TV) dye). Iron, Hg, In (III), Ga (HI), Pd(II), Ce(IV), Au(Iin, Sn(II), H(III), MoO*. W O ^ and UO„2 interfered, 2 4-(2-Thiazolylazo)- 5SSnm To a test soln. (pH 5,6.5 ml) containing 1 to 20 /tg 140 resorcinol (I) «=25,500 of V(V) is added 1 ml of 2 mM (I), and 2 ml) 1 M- and either of: acetate buffer of pH 3.9. The complex is extracted Tetraphenylarsonium by shaking the soln. for 10 min. with 5 ml of 5 mM chiwide (II) (II) or (III) in CHClg. The absorbance of the orga­ Tetraphenylpbosphonium nic phase is measured against a reagent blank. The chloride (III) calibration graph is rectilinear for 0.1 to 4.0 ¿ig/ml of V. The coeff. of variation was 2 to 10%. Cu, Co, Ga, and Fe(III) interfere at concn. of <10% of that of V.

Haemataxyiin and 610 nm The cited system forms different ternary complex- 141 hexadecyltri- «=9100 es in presence and absence of ascorbic acid. The tnethylammonium bromide complex formed in the presence of ascorbic arid is very stable and can be used for the determination of fig amounts of V. Beer’s law is obeyed for up to 4 ppm of V. The Sandeli sensitivity is S 3 ng/cm2. The coeff. of variation for 2 ppm of V is 1%.

N-(4-Chlorophenyl)- 620 nm The test soln. (2 drops) is treated with 1 drop of 142 N'-(5-chloro-o-tolyl)- «=200 3M-acetic acid and shaken with 0.5 ml each of 3M N-hydroxy-p-toluanudine reagent and 0.08M-2-naphthol, both in CHClg. A hydrochloride greenish-blue complex is formed which is stable for > 30 hr. The detection limit is 0.07 /xg of V at dilution of 1 in 5x10 . Tolerance levels are e.g. W(VI) 15; S, Ti(IV) and Zr 60 and Mo(VI) and Cu(II) 300. The method is used for detection of V(V) in water samples. Name o f the Reagent X o r Remarks Refs. m ax. pH working wavelength with«

^ -ffy d rc o ^ ’mS'- 400 nm 4 to Spectrophotometric studies of the complexes of U 143 dimethylacetophenone (I) 6 (VI), V(V) and Mn(II) are reported. Vanadium & 3’-Bromo-2'-hydraxy- (V) forms with (I) and (II) orange complexes that S'-methyl-acetophenone (II) are soluble in 50% V/V ethanol, for which absorbance is measured. n ’n 2-bis-(4-Chloro- 570 nm 7M A soln. containing 100 fig of V was treated with 10 144 phenylJ-NMiydroxy- acetic ml ofanhyd. acetic acid and diluted to 25 ml with benzamidine add H20, then 6 ml of a 0.1% of reagent soln. in CHClg was added with shaking for 1 min. The organic phase was separated and dried over Na S04, then diluted to 25 ml (two 5 ml portions of CHClg used to wash the aq. phase being added) and its absorbance was measured. For determining the V in steel the sample is treated with aqua regia and the resulting WO ppt is thoroughly washed with hot HgO, 1M-HC1 and hot 1M acetic acid which retains V; pH is adjusted to 7M in acetic acid before extraction and determination of V. Beer’s law is obeyed for 0B to 12B ¿ig/ml, the coeft of variation for 150 fig of V was ± 0.63% (30 determinations). Interferences from W(VI) could not be masked and many species interfered. N 1-Hydroxy-N1-m- 365 nm - The method is based on extraction of V into 145 totyl-N2-(5-chloro- to CHC1 as a ternaty complex with cited reagent and o~tolyl)-p-toluamidme 620 nm one of the named adducts. The absorbance of the hydrochloride with: final CHC13 extract is measured at appropriate pH carboxylic add, and wavelength which depends on which of the 40 phenols, aldehydes, adducts is used. The Sandell sensitivity is — 0.01 thiocyanate and azide jig/cm2. There is no interference from Fe(III), Cr(III), Mn(II), Ti(TV), Z r, Mo(VI), Cu(II), Zn, Ni(II), C0(I1) or AL Initial separation of Fe (e.g. in alloys) is not necessary.

N-4-CMorophenyl- 2 Vanadium was determined by extraction from a me- 146 N*-(5-chIoro-o-tolyl) dium of pH 2 with a soln. of (I) and a carboxylic N-hydroxy-p-toluamidine acid in CHCIg and absorbance of the 1:2:1 V. (I)- hydrochloride (I) and carbaxyiic add complex in the extract was meas­ Benzoic add (II) 575 nm ured. For the different carboxylic acids, the ppm 2-Chlorobenzoic add (HI) 575 nm range over which Beer's law is obeyed and the 4-Oilorobenzoic add (IV) 580 nm coefL of variations were: 1.5 to 8.8, 0.77% for (II); Salicylic add (V) 580 nm 1.0 to 8.2, ±0.72% for (III); 1.0 to 8.4, ±0.58% for Acetylsalicylic add (VI) 580 nm (IV); 1.0 to 9.0, ±0.61% for (V); 1.0 to 9, ±055% Naphtbalic add (VII) 580 nm for (VI); 1.0 to 8.0, ±0.8% for (VH). The method was used to determine V in steel.

2,4-Dimethaxy-N-p- 570 nm H a The blue-violet 1:2 VOa + -I complex was extracted 147 tolyl-benzo hydraxamic «=5900 medium from HC3 medium into CHC1, and absorbance ad d (p-TDMBHA) (I) of the organic phase was measured. Beer's law was obeyed for 0.1 to 9.0 ppm of V. The method was used to determine V in steel and phosphorite in/tg quantities. G* Name of the Reagent X o r pH Remarks Re£ max. working wavelength withe

Isopropylidenehydrazide (I) 540 nnt The sample of steel is dissolved in a mixture of Sulphonitrazo, [8-hydroxy- H3P 04> HO, H N03 and heated to fumes with 7-(2-hydrc«y-5-mtro-3- H S04. An aliquot containing 30 to 100 /ig of V is sulphophenylazo)-naphthalene- mixed with KM n04 and HC1, the V is extracted 1-,6-disulphonic acid],N- into a 02% soln. of (II) or (III) in CHG3, and the phenyl benzohydroxamic absorbance of the extract is measured. Alternative­ acid. (II) 530 nm ly, the sample can be dissolved in H3P 0 4 - H2SC>4, N-Phenyicinnamohydraxamic and mixed with soln. of KMnC>4, NaNO and urea; acid. (Ill) 540 nm an aliquot containing 30 to 150 jug of V is then extracted with a 0374% soln. of (I) in acetone, and the absorbance of the extract is measured.

N<23-Xylyl) 525 nm = 6N The sample soln. (containing <50|tg of V) is trea­ cinnamohydraxamic acid in H Q ted with 40 /it of 03% KM n04 soln. and after 5 min. with 5 ml of a 0.1% soln. of the reagent in C 0 4. The aq. phase is adjusted to — 6N in HQ and the complex is extracted into C 0 4 by shaking for 3 min. The CQ4 phase is separated and dried with Na2S04 and filtered; the absorbance is mea­ sured against CQ 4. Many co-existing elements in steel do not interfere, nor does H 0 0 4 (up to 3M). 4-Hydraxy-3-{5-hydroxy S45 nm A 1:1 complex is formed with reaction of the named 150 benzo [aJ-phenazin-6- reagent and vanadate which is extractable by ylazo} benzene sulpbonate CHClg or cyciohexanol, for spectrophotometric in presence of Septonex measurement. The reproducibility of the reaction [ethoxy carbonyltrimethyl is improved in presence of septonex. From 5 to 15 pentadecyl ammonium fig of V in the final vol. of 50 ml can be determined. bromide]. Trace amounts of Fe(II), Fe(III), Co, Cu(II) and U(VI) interfere, but after addition of Cd, EDTA, Fe(III) and Co(10-fold excess) and Cu(ll) (5-fold excess) can be tolerated.

[Isophthalaidehyde 490 nm To determine V in steel, the sample is dissolved in 151_ bis-(2-hydroxyaml)] 50 ml of HgS04 (1:4) plus a few drops of HNO^; the soln. is evaporated to fumes. The residue is heated with HgO (50 to 60 ml) to dissolve the salts, cooled and treated with KMnO^ (excess being re­ moved with oxalic acid) to oxidise V, diluted to 100 ml with HaO. To a portion of this soln. [10 ml for a V content <1%, or 5 ml diluted with 5 ml of H S04 (1:9) for 1 to 2%] are added 5 ml o f' H gP04, 20 ml of H2S 0 4 (1:1), 5 ml of 0.03% reagent soln. in 6M-H2S 04 and HzO to give 50 ml. After 30 min. the absorption is measured against a blank containing all the chemicals except the reagent. A reagent blank value, determined by • analysis of Iron-Carbonyl, is deducted from the results, and V content is found from a comparison with standard samples. Tervalent Fe is masked with HgP 0 4; Cr, Ni, Ti, W and Cu do not interfere. Name of the Reagent X or Remarks Refs. m ax. working wavelength with«

2,6,7-Trihydroxy- 660 Dm The reagent is recommended for determination of 1.52 9-{2-hydroxy-phenyI)- «=*47500 (V(IV) or V(V) (V(V) is reduced to V(IV) during 3H-xanthen-3-one (1) the reaction with I)]. The V(1V)-I (1:2) complex is formed at pH 3.7 to 4.7 in an aq. medium contain­ ing 1.4% of ethanol and at least two-fold molar excess of (I) [relative to V(IV)] and 0.2 oM hexadecyl trimethylammonium ion. Beer’s law is obeyed for 0.08 to 0.8 /ig/ml of V. The selectivity of the reaction is poor.

3- Hydnoxy-2-methyl- 450 mn A 5 ml aliquot (containing 10 to 100/¿g of V) is 153 1-phenyl pyridine- and adjusted to pH 1.6 with H2S 04, 1 ml of 6 mM KSCN 4- one 660 nm is added and the mixture is diluted to 10 ml (HgO). or The soln. is extracted by shaking for 15 min. with 3-Hydraxy-2-methyl- 10 ml of 0.4 mM of either of the reagents in CHC13; l{p-toly1)-pyridme- the extracted complexes are stable for 24 hr. Beer’s law is obeyed over the range 1 to 10 ppm of V. Iron (III), Mo(VI), Ti(IV), Pd(II), W(V1) and Zr should be removed before extraction. Many anions and cations did not interfere. 3-(l-S-Dihydrojy- 580 nm 25 Tervalent V forms a red 1:2 complex with this re- 154 3,6-disulpbo-2-naphthylazo)- agent at pH 25. Beer’s law is obeyed for 0.1 to 6.0 2-hydraxy-5-sulphobenzoic /xg/ml of V at a reagent concn. of 0.2 mM. Tervalent add. Fe, Al, Ti(IV) and Ti(III) interfere.

N'-(4-Chloro-o-tolyl)- 610 nm(H) The dted reagent I reacts with V(V) in SCN" or 155 N-hydroxy-N-p-tolyl «*6000 N3* medium to form a 1:22 (V-I-anions) complex benzamidine hydrochloride, (I) extractable in CHC13, their absorption is meas­ Thiocyanate (II) or ured. Optimum analytical range for determination Azide” (III) 590 nm (III) of V(V) are 1.0 to 72 and 12 to 8.4 ppm with the «*4800 use of SCN* and N3‘ respectively; at the 4 ppm level the coeft of variation were 0.64% and 0.72% respectively. Mo(VI) forms a CHC13 soluble com­ plex in each system, but does not interfere. The method was used to determine V in steel after removal of Was hydrate WOg. 4-Methoxy-N-tolyl- 570 nm L8 A 1 ml portion of the V soln. (0.1 mg/ml) is mixed 156 benzohydroxamic add with 6M-HC1 and HzO to give a pH of 1.8 in a voL and thiocyanate of 15 ml; 5 ml of the reagent (0.05% in CHC13) and 10 ml of CHC13 are then added and the mix­ ture is shaken for 10 min. before 5 ml of 2% NH^SCN soln. is added and shaking is continued for a further 5 min. The dark blue violet CHCI3 layer is separated and the aq. phase is washed twice with 5 ml of CHC13. The combined CHC13 soln. are diluted to 25 ml and absorbance is measured against CHCI3. Beer's law is obeyed for 0.5 to 12 ppm of V. The method is used for determination of V in ligand speed steel. oo o Name of the Reagent o r pH Remarks Refe. wotting wavelength withe

1-[(6-Methyl-2-pyridyl- S62 nm 3M in The reagent is prepared by coupling diazotised 157 azo)-2-hydraqrnaphthalene H2S04 2-amino-6-methyl>pyridine-N-axide with 2-naph- N-oode[2-(2-Hydraxy-l- thol (1:1 molar ratio). For the determination, a naphthylazo)-6-methyl soln. (10 to 100 jig of V) is made 3 M in HgS 0 4 and extracted with CHC1 after addition of 5.0 ml pyridine N-arideJ. 3 of ethanolic 0.05% reagent Interference is caused by HgS04 (>3M), H Q and HN03> The absorb­ ance of the extract is measured against a reagent blank. Beer’s law is obeyed for 0.4 to 4.0 ppm of V; the relative error at 1.2 ppm was +0.83%. The method has been adapted for determination of V in steel, see following reference.

The sample containing = 5 mg of V was dissolved 158 in 5 ml of aqua regia with gentle heating, 5 ml of H SO was added and soln. boiled to remove the 2 4 aqua regia, and residue dissolved in 50 ml of HaO with warming; then 0.5 ml of Br was added and the soln. kept warm for 20 min. before being boiled to remove excess of Br. After dilution with 700 ml of H O, 150 ml of H SO, was added and the soln. was made up to 1 litre with HaO; a slight residue of SiOa did not interfere. A 10 ml aliquot of this soln. (10 to 100 p,g of V) was diluted to 42 ml with 3 M- HgS04, 1 ml of ethanol was added, and after 10 min. 2 ml of H PO . was mixed in, followed by 5 ml of a 0.05% ethanohc soln. of the reagent. After 20 min. the soln. was extracted with CHC13 (10, 10 and 3 ml). The combined extracts were made up to 25 ml and dried with Na SO. and the absorbance a 4 measured against a reagent blank. The test soln. must contain more than 2 ng of Fe; a 10-fold amount of Co and a 5-fold amount of Cu are tolerated, but the amount of Ti must be one quarter (or less) of that of V. The result was satisfactory for standard steel with a standard deviation of 0.3%. Salicylohydroxamic 330 nm 1 to Physico-chemical characteristics of the complexes 159 add and 16N- of V(III) and V(V) with reagent in 1 to 16N- H SO medium have been determined. The 580 nm H2-S °4 2 4 complexes form the basis for determination of various forms of V. F and Fe interfere.

3,4-Methylenedioxy- 570 nm 4M To determine vanadium in steel the sample is dis- 160 N-p-tolyl in solved by 3M-HgS04 plus HNOg (added drop- cinnamohydroxamic add HQ wise). After evaporation and dilution, the V (40 to 200 /ig) in a portion, is oxidised to V(V). The soln. is made 4M in HC1, then extracted with a 0.1% reagent soln. in alcohol-free chloroform; the extract is dried and diluted to 25 ml and its absorbance is measured against a blank extract. Oxidising agents must be reduced initially by Fe(II). SCN" interferes seriously. Name of the Reagent A. or Remarks Refs. working wavelength withe

N-p-Methyl benzqyi- 560 run The cited reagent reacts with V(V) in HC1 medium 161 N-p-methyl phenyl- «=6400 (0.01 to 0.5 M) and further addition of SCN’ to the hydroxylamine reaction mixture at pH — 1 forms a stable blue- [N-p-tolyl-p-toIu- violet ternary complex extractable into CHQ3- hydraxamic acid]- The sample (0.6 g) is dissolved in dil. HgS 0 4 (1:4) thio cyanate and evaporated to a syrupy mass, repeating the process twice with 5 ml portions of concn. HgS 0 4 and once with 5 ml concn. HNOg. The soln. is heated to dense white fumes, cooled, diluted to 50 ml and then boiled to dissolve any solid matter, filtered and the residue washed with hot HgO and made up to 250 ml in a flask. An aliquot of the soln. is oxidised with 0.1% KMnO, soln., extracted and the org. phase washed with 2N HQ to back extract Fe(III) into aq. phase. The absorbance of the extract thus obtained is measured. Beer’s law is obeyed for 0.4 to 14 ppm of V. Fe(III), H(IV) and Pt group metals interfere seriously, but Fe(III) can be removed by extraction into ethyl ether from 6 to 8M-HQ medium. In application to standard steel ( — 2% of V) recovery was >97%. N-p-Methaxy- and 540 nm 6N- Both reagents react with V(V) in 1 to 4M-HC1 to 162 N-p-methyl-benzoyl- «=5552 HQ form blue violet complexes, extractable into N-p-methyl phenyl C H G . Procedure: an aliquot of metal soln. (100 hydroxyl amines; fig of V) is acidified to adjust the pH to 6N-HG, (N-p-tolyl-p-aniso 530 nm the soln. is extracted maintaining the voL of both and N-p-tolyl-p-tolu- «=5094 aq. and non aq. phase at IS ml. After shaking for S hydraxamic arid]. min. the blue-violet CHGa layer is dried over anhyd. Na2S04 and transferred into a 25 ml voL flask. The aq. phase is further rinsed with 5 ml of CHClg, which is after proper drying combined with previous extract. The voL is made up to the mark with CHC1 and absorbance measured vs. solvent 3 blank. Beer’s law is obeyed for 0.5 to 14 ppm of V with either reagent Ti(IV), Mo(VI), W(VI), Nb and Zr interfere seriously. Recovery was >98% with either reagent

Molybdophosphate 630 nm 1.5M . o the reagent are added 8 ml of liM -HQ; after 163 «=186000 in H a 2 min. 5 ml of 0.0185% malachite green soln. are : added. The mixture is diluted to 50 ml with H O and after 30 min. the dye molybdovanado- phosphate complex is extracted into 5 ml of nitrobenzene from 25 ml of aq. soln. The extract is dried over Na£S 04 and its absorbance is measured. The recovery of V is 99%, the calibration graph is rectilinear for up to 12 fig of V in the extract and the coeff. of variation for 0.1 fig in the extracts is ..... 1%. Name of the Reagent or pH Remarks Refs. working wavelength with e

2-Methaxy-N-m-tolyl 555 tun 6 to The test soln. was diluted with HzO and made to 8 164 benzohydraxamic acid 8M-HC1 M H O , the final voL was 25 mL The mixture was then shaken with 5 ml of 0.1M reagent in CHQ3 for 5 min. The organic phase was separated and dried over Na2S04 and diluted to 25 ml with CHC13 and absorhanee measured against a blank extract. Beer’s law was obeyed for 0.05 to 15 fig/ml of V(V). The method has been used for analysis of various fruits and vegetables, tobacco, rice, rat tissue and water (fresh and saline).

2-Pyridylacetal- 415 nm 1M- The sample soln. [10 to 50 ml containing < 100 /¿g 165 dehyde salicyloyl- 425 nm HCI of V(V)] is treated with 2 ml of 0.5M-KC1 and 1.5 hyd razone ml of 1M-HCI, then extracted with 10 ml of 0.05% of reagent soln. in CHC1 containing 3% (V/V) of dimethyl formamide. 'Hie absorbance of the extract after drying over Na S04 is measured at 425 nm against H _0 or at 415 nm against a reagent blank. Beer's law is obeyed for05to2ftg/m lofV in CHC13 at 415 nm. The method has been applied to determine V in high speed steel and commercial grade phosphoric arid. Viohiric acid 222 nm 95 The complexes of vanadium (V), niobium (V) and 166 tantalum (V) with violuric add were determined. The absorbance of soln. is increased by increasing pH, reaching max. at pH 9 5 for V(V), pH 9 for Nb(V) (Xmax = 212 nm) and Ta (215 nm) and with increasing ligand concn. The detection limit was 5.1,7.4 and 1.8 ppm for V, Nb and Ta respectively

N-Pbenyl benzohydraxamic 510 nm The sample is extracted with portions of pyridine- 167 acid H^O (15) until the extractant no longer becomes yellow, 5 ml of extract is heated with 15 ml of concn. HCl and a few drops of 1% (NH2)„SOg soln. to oxidise the V to V(V). Excess of s J j & is decomposed by boiling and the cooled soln. is treated with 10 ml of 0.05M-KL The liberated iodine is extracted into 0.1% of the reagent in CHC13 (10 ml then 2 x 5 ml) as the iodine complex, and the extract is diluted to 25 ml with CHCl3 before measuring the absorbance. The calibration graph is rectilinear for 0.05 to 035 ppm. The method has been applied to standard steel and ’ ferrotitanium containing 0.05 to 1.68% of V. The extract ion with aq. pyridine allows recovery of V- porphyrin complexes from petroleum without the need of ashing procedure. Name of the Reagent X or Remarks Refs. m ax. working wavelength withe

2-Methyl-4-(4-methyl- 560 nm A bluish-violet (1:1) complex with V(V) is formed 168 2-thiazolylazo) at pH 6 (acetate buffer soln.) in aq. 50% methanol. resorcinol The final soln. (25 ml) should contain 2.6 to 35.7 /xg of V and 1 ml of 1 mM-reagent for which absorbance is measured after 30 min. against a reagent blank. The optimum analytical range is 0.1 to 1.4 ppm of V, the relative error is 2.8%. Most common masking agents interfere seriously but tartrate, CN, F" and Ca-l,2-diminocyclo-hexane- NNN'N'-tetra-acetate do not and may be used as auxiliary complexing agents of Mn(II), Fe(HI), Ga, Cd, Ni(II), Cu(II), Bi, Zn, and In. The method has been applied for determination of 0.15 to 0.64% of V in low alloy steels.

Salicyl Quorone 520 nm Tetravalent V can be extracted as the V(IV)-salicyl- 169 [2,6,7-Trihydroxy-9- «=50000 fluorone-antipyrine (1:2:2) complex, from ammon- (2-hydroxy phenyl) ical acetate buffer medium of pH 4, into CHCIg xanthen-3-one] and ethanol (1:1) that contains 0.75M and 0.25 mM Antipyrine respectively of the reagents (ethanol is transferred to the aq. phase during the extraction). The organic phase is diluted (1:1) with ethanol and its absorbance is measured. Beer’s law is obeyed for 2 to 30/iM - V(IV) or V(V) [V(V) being reduced to V(IV) during extraction].

Chromotropic acid 430 nm Chromotropic add (1.0% soln.) and KBrC>3 (2% and K Br03 soln.) are injected into a manifold at 0.35 mlftnin and mixed at a PTFEY-shaped joint, and the mixture is passed into a coil (150 cm x 03 mm i.d.) into which the sample (30 /d aliquots) is injected and absorbance is measured. 03 to 4.8 ng (10 to 160 ppb) of V can be determined, the coefL of variation being 20% at the 60 ppb level Sixty samples can be analysed in 1 hr.

Oxine [quinolin-8-ol]. 475 nm Optimum conditions have been established for for­ mation of the V(V) complex with cited reagent and extracting it into isoamyl alcohol for spectrophoto- metric measurement. The optimum analytical range is 0.75 to 3.5 /¿g/ml of V and Sandell’s sensitivity is 5 ng/cm2. The method has been used to determine V in pilchards and potatoes.

4-Bromo-N-(o-tolyl) 530 nm 6 to The reaction of 10 atyl hydroxamic adds with benzohydroxamic acid <=4000 8M-HC1 V(V) in 6 to 8 M-HC1 was studied. The spectral characteristics of the coloured V-atyl hydroxamic add complex extracted into CHClg are recorded. An extraction spectrophotometric method is described for determination of V with dted reagent. Beer’s law was obeyed for 03 to 8.0 ppm. The method is applied for determination of V in standard steels. Name of the Reagent or Remarks Refs. working wavelength withe

N-Cinnamoyl-N-o-methaxy : 530 nm In the medium of 2 to 5 M-HC1, both reagents I 173 phenyl hydnnylamine [N- and II form (1:2) complexes with V(V) that can be (2-metboxy phenyl) cinnamo- extracted into CHCl9 for measurements of absorb- hydroxamic acid] (I) and ance. For determination of V in steel, the sample is N-Cinnamoyl-N-p-methoxy 550 nm dissolved in diL H2S 0 4> evaporated to fumes phenyl hydraxylamine with concn. H„SO.concn. HNO. and oxidised [N-p-tolyl cinnamohydroxamic with KMn04> For determination ofV in rock, the acid] (D) powdered sample is fused with KHSC>4 and HaSC>4 is added to the melt, the soln. is heated, neutralised and concentrated, Ti and Fe pptd. by aq. NHg and filtered off. The filtrate is acidified and V in the soln. is oxidised with KM n04 and determined in the presence of an excess of F' with reagent (I). Beer's law is obeyed over the concn. ranges 1 to 14 ppm and 0.4 to 14 ppm of V (optimum ranges 1 to 10 ppm and 1.4 to 10 ppm) for complexes of I and II, respectively. Ti(IV), Mo, W, Nb(V) and Zr(IV) interfered.

N-p-Methoxyphenyl-2- 545 nm To 5 ml of 0.5 mM - V(V), to which a slight excess 174 furohydroxamic acid of KMn04 had been added, were added 5 ml of 8 to 12 M-HC1 and 5 ml of cited reagent (0.1M) in CHCI3. The organic phase was set aside and the aq. phase extracted with more reagent; the combined organic phase was dried (Na^O^) and washed with reagent after use. The dried extract and washings were diluted to 25 ml with C H Q 3, and absorbance was measured against a reagent . blank. The method has been applied for determination of V in pond water, phosphate rock and steel. Beer’s law was obeyed for up to 12 ftg/ml of V(V) and interference from Ti(IV) could be prevented with F .

N-Cinnamoyl-N- 535 nm 35 Pentavalent V reacts (in 3.5 to 9 M-HQ medium) 175 (2 5 -xylyl) hydroxyl- to with the named reagent to form a stable 1:2 com­ amine [N-(23-xylyI) 9 M- plex that is extractable into CHQa; the absorption cinnamohydroxamic acid]. H Q of the violet soln. is measured. Beer’s law is obeyed for 05 to 7 ¿ig/ml of V in the extract. Interference from Fe(II) and Ti(IV) is masked by HgP04 and NaF, respectively. The method has been used for determining V in petroleum and results are good as compared to those of a.as.

2,6,7-Trihydroxy-9- 565 nm 5 A modified method described by Asmus and Jahny 176 (3-pyridyl) xanthen- for detn. of V is used. First V(V) was reduced by 3-one (I) ascorbic acid, then V(IV) was caused to react with (I) at pH 5 in aq. 20% methanol contg. polyvinyl alcohols as protective collide. The absorbance of oo VO V(IV)-I was measured after 30 min. The calibra­ tion graph was rectilinear for up to 0.1 ppm of V and detection limit was 0.012 ppm. Name of the Reagent X or pH Remarks max. Refs. working wavelength withe

Z6,7-Trihydroxy-9- 520 nm 3.7 Tetravalent V forms coloured (1:2) complexes with 177 (2-hydroxyphenyl) to to 2,6,7-trihydroxy fluorones at pH 3 to 5, «=40,000. xanthen-3-one 525 nm 4 3 Cited reagent forms a coloured complex with e=50000 V(IV) in aq. 30 to 60% propanol. The complex is extractable by benzene and its halogen derivatives, CCI4, higher alcohols, ketones, ether, and halogenated alkanes. Toluene and xylene extracted the complex partially and the alkanes negligibly. No (or weak) extn. is observed in propanol, methanol, isopropyl alcohol, acetone, dioxan, dimethyl formamide or dimethyl sulphoxide. H ie optimum pH for extn. is 3.7 to 4.3. Beer’s law is obeyed for 0.1 to 1.0 /¿g/ml of V. Pentavalent V reacts similarly: spectrophotometric detn. of V is possible after removing Sn, H , Sb, and Mo by extn. with the reagent from 30% propanol at pH 1.5 to 2.

N-Anthraniloyl- 630 nm 0.95 To the sample soln. were added H Q (final pH 178 hydraxamic acid «=6750 0.95), 5 ml of 1% N-AHA soln. in isobutyl methyl (n-AHA)and ketone (IBMK) and 5 ml of aq. 2% NH4SCN, the Thiocyanate ion. vol. of aq. phase being adjusted to 15 ml. The organic phase was dried with Na2S04, its vol. ad­ justed to 25 ml and its absorbance measured against IBMK. Beer’s law is obeyed for 0.5 to 12 ppm of V(V). The lowest tolerance limits are 20 ppm for Fe(III), W(VI) and Nb(V), 40 ppm for Mo(VI), 50 ppm for Ta(V) and 80 ppm for Ti(IV), Mn(II) and Zn(IV), all (except for W and Mn) in the presence of F".

N-4-Chlorophenyl- 530 nm 4M- Estimation of V(V) and n (IV ) in aluminium con- 179 N-hydroxy-benzamide (I) H Q taining borides is described. The sample (2 g) is dissolved in H O , and the soln. is made up to 100 ml with 4M-HO. For detn. of V, 25 ml of sample is heated with a few drops of dil. aq. KMn04, the cooled soln. is extracted with 0.05% soln. of the reagent in CHOg and absorbance of the violet V(V) complex is measured. Absorbance of Ti(TV) complex is measured at 380 nm. The coeft of variation is 4.4 or 43% for the detn. of 3.2 /¿g/ml of Ti or V, respectively. There is no interference from Zn, Mg, Ga, or Fe(III).

N-Phenyl benzo- 525 nm 4M in The method involved oxidation of V to V(V) with 180 hydraxamic add t=5100 H Q formation of its complex with cited reagent which is extractable into CHC1 from 4M HC1 medium. 3 Absorbance of the extract is detd. spectrophoto- metrically. For detn. of 40 to 120 /tg/ml of V in soil, the relative error did not exceed 2.5%. Name of the Reagent Xm a x or Remarks Refs. working wavelength withe

Leuco-base [4,4- 725 nm The method is based on the catalytic effect of V on 181 iminobis (NN-dimethyl) the oxidation of I to Bindsch Elder’s green by aniline] (I) KBrOg under following conditions: 0.75 mM-I, 32 mM-KBrOg, 2.1 mM-F', pH 3.8; absorbance was measured after reaction at 25‘C for 10 min. A rectilinear relationship was obtained between absorbance and V(IV) concn. in the range 0 to 12 /ig/ml. Up to 8 Pg/ml of V can be determined and sensitivity (for an absorbance of 0.001) was 0.15 Pg/ml. The coeff. of variation of 60 fig/ml was 3.5% (n=10). Fe + and Cu2+ caused acceleration effects, but that due to Fe3+ was eliminated by addition of F"; up to 10,000-fold excess of other ions did not interfere. The method was used to determine traces of V in river water and potable water.

The solns. of I and KBrOg are mixed and the sam- 182 pie soln. (20/¿l) is injected into this stream, which passes through a PTFE reaction coil at 25". The absorbance of the Bindsch-Elder’s Green formed by oxidation of I is measured in a flow-through cell With use of 1.6 mM-1 and 64 mM-KBrC>3 at pH 3.8 a calibration graph that is rectilinear for up to 80 ppb of V(IV) can be obtained. Detection is possible =* 40 sec after injection, and up to 60 . samples can be analysed in 1 hr.

4-Benzoyl-3-methyl-l- 490 nm 3 The sample soin. [10 ml, containing up to 100 fig of 183 phenyl pyrazolin-5-one V(V)] is treated with 10 ml of acetate buffer soin, of pH 3.0, diluted to 30 ml and shaken for 5 min. with 5 ml of CHCI3-butanol (4:1) containing 0.1% of the cited reagent After centrifugation the absorbance of the separated organic layer is measured. Out of 24 metal ions tested, Fe(IlI), W(VI), Ti(IV) and Mo(VI) interfere seriously. Results for three Japanese-standard steels are given. '

4-Hydrazinobenzene 454 nm In the presence of C103" and with tartaric acid as 184 sulphonic acid (I) ■ activator, V(V) catalyses the oxidation of I into 4- with m-phenylene sulphobenzene diazonium ions which couple with diamine (II) n to form a yellow dye, exhibiting max. absorption at 454 nm. The calibration graph is rectilinear for up to 40 ng/ml of V(V) and coeft of variation (4 detn.) for 8,24 and 40 ng/cm of V are 2.1,2.7 and 2.0%, respectively. Interference is caused by >5 fig of Fe(II), Fe(III) or Se(IV), 1 fig of Cu(II) or u>VO Mo(IV) or 10 fig of A t Name of the Reagent A. or pH Remarks Refs. m a x. r working wavelength with«

Tridodecylelhyl- 570 nm 5 A sample (up to 5 fig of V(V) in 1M-H2SC>4) was 185 ammonium bromide mixed with 3 ml of aq. 0.5 mM-catechoi violet. The pH of the soln. was adjusted to 5 with 2M-Na acetate, diluted to 20 ml with H?0 and mixed with 5 ml of 5 mM of cited reagent in CCl^. After separation, the absorbance (stable for 30 min) of the CC14 layer was measured. No interference was observed on 225 fig of V(V) when 0.1 mg of Cd, Co, Or, La, Pd, Mg, Mn, Hg, Ni, or Zn was present, but Al, Be, Bi, Fe(III), Mo, Sn(IV), Th, U, and W interfere seriously, as did such anions as SCN*, a 0 4', citrate and EDTA (at 10 mg level).

Sodium, N-phenyi- 370 nm 0.1 to Spectrophotometricdetn.ofV(V),Ti(IV)and 186 2-sulphobenzo- «=2750 0.5 Mo(TV) with cited reagent is described. The cited hydroxamate (I) M HO reagent (I) forms a V(V)-I (1:2), Mo(VI)-I (1:2 or T1(IV)-I (1:1) complex in aq. medium that is 0.01 to 0.5 M in HC3 (for V), 0.1 to 2M in HC1 (for Mo) o r 0.03 to 0.1 M in H O (for 11); at least a 100-fold molar excess of I over the metal is needed. Mo(VI) exhibits max. absorption at 340 nm, «=2320 and Ti(IV) at 330 nm, «=3500. Beer’s law is obeyed for 0.4 to 4 fig/ml of V, 4 to 80 /ig.ml of Mo or 0.8 to 14/tg/ml of TL Nickel, Co, Cr(II), Cu, Nb, Ta, Zn, Pb, Th, Cd, Al, Sn(II) and La do not interfere. The method was used for detecting 0.1 to 25% of V in refractory alloys. The coeff. of variation <2.6% (4 to 10 results).

N*-(5-Chloro-o-tolyI)- 580 nm 0.6 The test soln. [100 fig of V(V)] was adjusted to pH 187 N1 -hydroxy-N1 -m- e=5450 to 0.6 to 55 with H O and ammonium acetate, diluted tolyl-p-toluamidine 5.5 to 25 ml and extracted for 1 to 2 min with 5 ml of hydrochloride (I) 0.15M-I and 10 ml of 0.06M-aspirin in CHC13- The in presence of salicylic, separated aq. phase was washed with C H ag and anthranilic and phthalic discarded, and the combined CHOa extracts were acid. dried (NagS04) and diluted to 25 ml for measure­ ment of absorbance. Beer’s law is obeyed for up to 9.4 ppm of V and the coeft of variation was 0.56 to 0.84%. Of diverse metal species and anions investigated, only W(VI) interfered seriously.

N-m-ChIorophenyl-2- 520 nm 5 to O ted reagent and V(V) form a 1:2 complex in the 188 t heno-hydracamic acid (I) e=5850 8M- medium 5 to 8 HCI, used for absorbance measure­ alone or in presence of HCI ments. Further addition of SCN in 300-fold excess thiocyanate - 580 nm results in the formation of a blue complex extract- «>7000 able into CIIC13 for detn. of V at 580 nm. Beer's law is obeyed from 0B to 4.8 ppm of V. There is no interference from 5 anions and 23 cations [inclu­ ding those of Mo(VI), W(VI) and Zr(lV), which interfere in the determination in absence of SCN']; Ti(IV) interferes. The method has been applied for detn. of V in steels. VO Cv Name of the Reagent PH Remarks Refis. working wavelength withe ,

N-Phenyl-p-phenylene 735 nm The oxidative coupling reaction of I with II in pre- 189 diamine with (I) sence of KBr03 (oxidant) and N-tartrate (activat­ NN-dimethyl aniline (II) or) is catalysed by V(TV) o r V(V) at 50*, giving a green product used for absorbance measurement after 20 min. The optimum final concn. of the respective reactants are 50 /tM, 1.6 mM, 2 mM and 60 mM, and Beer’s law is obeyed for 0 to 1 ng/ml of V. Sandell sensitivity is 1 3 Pg/cm2 and coeff. of variation is 23% [10-detn. of 1.0 mg/ml of V(V)]. Fe(III) (> 0.01/tg/ml) and Cr(VI) (> 0.02/ig/ml) interfere but Cr(VI) can be reduced by ethanol to Cr(III), which is tolerated. The method has been applied to determine V in sea water. The recovery of added (1 ng/ml) is quantitative.

N-Phenylbenzo- 530 nm HQ The sample soln. (1 g) in aqua regia is evaporated to 190 hydroxamic acid dryness and residue is treated (x 3 or 4) with concn. HQ and then taken up in 10M-HC1 and diluted to 50 ml with HC1. After addition of 03g of KG1, the soln. is extd. with tributylphosphate- kerosine (1:1) and the extract is washed with 10M- HCL The combined acid phase is evaporated with H2S04 (1:1) and concn. HNOg to decompose or­ ganic matter, the residue is dissolved in HaO and 0.1M-KMnC>4 is added in a slight excess. The mixture is acidified with HC1 and V is extracted into 10 ml of 0.2% reagent in CHC13, diluted to 25 ml with CHC13 and its absorbance measured. The method can be used for analysis of steel containing — 30 ppm of V. .

p-Sulpho benzene 495 nm 5 The sample (100 mg) is dissolved by gently warm­ azo-4-(50-chloro-2-, ing with 5 ml of H20 , 5 ml of concn. H Q and 1 ml 3-dihydraxypyridine) of concn. HNC>3 and evaporated to nearly dryness; [4-(5-chlor-230 the residue is dissolved in 5 ml of concn. H Q . Iron dihydroxy-4-pyridylazo) from soln. is removed after addition of 10 ml of benzene sulpbonic acid] concn. HQ and 4 mg of (NH4)2S04FeS04-6H O by extn. with 25 ml of isobutyl methyl ketone. ‘Hie aq. phase is evaporated to dryness, the residue is heated with a little cone. HNOg and the product is dissolved in H20 . At pH 5.5 the soln. is diluted to 100 ml. A 0.25% reagent soln. (5 ml), 5 ml of acetic add, acetate buffer of pH 5 and HgO to give a final vol. of 25 ml are added to an aliquot (1 to 10 ml). The mixture is heated for 10 min. at 60* to 65*, and its absorbance measured against a reagent blank. For calibration, a standard soln. of VO NH4V 0 3 is used. The relationship between absor­ bance and concn. is rectilinear for 1 to 10.5 /¿g/ml ofV. Name of the Reagent \nax.or pH Remarks Refe working wavelength withe

4-(2-Pyridylazo) 560 nm 4.7 Vanadium (V), Nb and Ta were separated by extn. resorcinol of V and Nb at pH 4 from O.OIM-Na succinate medium with trioclylamine in benzene. The V was re-extracted into acetate buffer soln. (pH 4.78) and determined with cited reagent. Nb was detd. with KSCN at 430 nm. Both complexes were stable for >24 hr. and Beer’s law was obeyed for 0.5 to 2 3 /t£ V or 1 to 8/tg Nb per ml of organic phase. With 10 /tg of V, 100 /tg of Hf(IV), 250/rg of Bi(III), 500/tg of Mn, Sn(II), Sb, Zr(IV) or Te(rV), 1 mg of Pb, Se(IV), Nb, citrate or oxalate and 5 mg of O ', F , N 03' or tartrate did not interfere; Cd, EDTA and phosphate interfered seriously. o -Phenyiene diamine (I) 440 nm 0.2M- The method uses catalytic action of V on the oxid­ or 2A4-Trimethyi-1,2- Ha ation of an organic reagent by KBrOg in the pre­ dihydroquinoIine-6-ol (II) 405 nm " sence of Tiron as activator. The test soln. (pH 3 to 4) containing <0.01 /tg of V is mixed with 1 ml of lM-acetate buffer soln. (pH 3.2), 0.6 ml of 0.25M- KBrOs and 0.2 ml of 0.25M-Tiron and diluted with H20 to 5 ml, then mixed with 1 ml of 0.02M-HQ containing either 0.01M (I) or 2 mM of (II). The rate of oxidation of the diamine or the quinolinol is determined from the rate of change in respective absorbances. The V content is found from a calibration graph. Interference is caused by 100- fold amounts of Cr, Mo(VI), EDTA or oxalate, but a 100-fold amount of Fe(HI), Cu(II), Ag, W(VT), H(TV) or Zr can be tolerated. A determination takes 20 min.

l-Amino-4-hydraxy- 450 nm 0.5M- Vanadium is determined selectively with the cited 194 anthraquinone HCI reagent (R) at pH < 2 [up to (0.5 to 5 ppm) of V(V) in 0.5M-HC1] by measuring the absorbance of 1:3 V(II) - R complex. The method is also applied to the determination of Fe(III), UOg and Ce(IV). At equivalent levels to that of V(V) present, Pt(II), Au(III) and Ce(IV) interfere.

N-(4-ChlorophenyI) 540 nm 4M A steel sample is dissolved with 3 to 4 ml of 12M- 195 4-methcKybenzo- in H2S 0 4 and a few drops of concn. HNOa and hea­ hydroxamic add HCi ted to fumes, cooled and diluted to 100 ml with H20. A portion of soln. is made 4M in HCI in a total voL of 25 ml and shaken with 10 ml of 5 mM of cited Feagent in CHC13. The absorbance is measured after dtying the organic phase with (Na2SO ) and diluting to 25 ml. Beef’s law is obeyed for 26 to 27 ¿ig of V in the final soln. The working range is 1.9 to 6.6 ppm of V, and coeff. of variation is 0.65%. Only Fe(II), Mo(VI) and Zr interfere seriously. Results have been obtained for standard steels and were in good agreement with certified values. Name of the Reagent \nax.or Remarks Refe. working wavelength with «

N-4-ChIorophenyl- 535 nm The dted reagent has been used for detn. of 20 to 196 2-naphthohydroxamic 320 ppm of V in 8 types of rocks, 0.01 to 7.25 ppm add of V in 19 biological samples (mostly crops, but including water and rat .tissue) and 0.06 to 1.68 ppm of Vin steels. For best results, a 0.1% soln. of reagent in CHClg was shaken for 5 min. with test soln. in a medium o f 8 M - HCI. The complex was stable for 10 days and its absorbance was measured. Beer’s law was obeyed for 0.09 to 20 ¿ig/ml of V, and the sensitivity was 9 ng/cm . Barium, Cd, Ca, Co(II), Cu(II), Mn(II), Zn, Fe(III), Pb(II), Ni(II) and AI in 60-fold excess (relative to V), Hg, U(VI) and Ce(IV) in 80-fold excess, and Os(VI) in 100-fold excess did not interfere. Interference by 60-fold excess of Ti(rV), Mo or Zr was prevented by adding NaF and ammonium oxalate before extraction.

N-(p-TolyI) cinnamo- 590 nm Vanadium (V) can be extracted as V-I-SCN (1:2:1) 197 hydroxamic add (I) complex into CHC13 at pH 1. Thè absorbance of and thiocyanate ion the extract is measured and Beer’s law is obeyed from 0.5 to 12 ppm of V. The method has been applied for detn. of V in steels after dissolution of sample in HgSO^. Fe(II) and Ti(IV) interfere. N-4-ChIorophenyl- 530 nm The V(V) is extracted with an 0.1% reagent solu- 198 2-naphthohydroxamic tion in CHC1 from 4 M-HC1 medium to form a 3 add violet complex, absorbance of which is measured at 25* against CHClg. The reagent is used in 8-fold molar amount relative to V(V); the calibration graph is rectilinear for 34 to 224 fig of V in 25 ml of extract, the Sandell sensitivity is 8.9 ng/cmz and the mean error is 2.5%. Tetravalent Ce, Mo(VI), Ti(IV) and Zr(IV) are tolerated even in high concn. but Pd(II) and W(VI) should be removed initially, and Cr(VI) and Mn(VII) should be reduced. The concn. of acetate and CIO^" should not exceed 6M and 1M, respectively. The prepn. and spectral properties of the solid complex VOC1 ( C ^ N C ^ d ) , are described.

4-(2-PyridyIazo) 550 nm To the soln. remaining after filtration of a water 199 resorcinol (I) sample, or of a suspension of rock sample fused with and Cu(II)-Trans-l,2 NagC 0 3, are added lM-acetic acid and 0.1M of II, diaminocydohexane- and pH is adjusted to 6 with aq. NHg [to avoid NNN'n’-tetni acetic interference from Mo(VI)]. The soln. is passed add (II) through a column (20 cm x 16 mm) of Sephadex G- 25 and V is desorbed with 0.12M-HCL. After addi­ tion of Na-acetate, the eluate is evaporated to dryness. The residue is dissolved in acetate-II- buffer soln. (pH 5 3 ) and 0.2 tnM of (I) and after 1 hr. the absorbance of the soln. is measured. Recovery of a fig/l level of V in standard rocks and sea water is good. w Name of the Reagent \nax.or pH Remarks Refs. working wavelength withe

Trihydroxy-xanthen 520- 4.5 to The complexes of V(IV) with cited reagent can be 200 3-one 530 nm 5 extracted into a 7:3 mixture of C3 to C8 alcohols with CCI4 or CHCL from an aq. medium of acetic buffer soln. (pH 4.5 to 5). Beer’s law is obeyed for 1 to 10 ftm - V(IV). Similar complexes of Mo(VI), W(VI), Ti, Zr, HF, Sn, Ge, Nb, Ta, Sb and Bi are extracted into the same solvent, but at pH 1.7 to 1.9, and V can thus be separated from equivalent amounts of the named metals by extn. first at pH < . 2 (diverse metals) and then at pH 4.8. The method was used for detg. 1 ¿ig/ml of V in the presence of 1 to 2/ig/ml of Hg, Sb, Mo, Mn, Ti, Sn and the coeff. of variation was 2% (eight results).

Propericiazine 496 nm 10M- The test soln. [containing 2 5 to 165 ng of V(V)], 201 {pericyazine; [2- e=9000 HgP 0 4 was mixed with 15 ml of 10M-H3PO4 and 1 ml of a cyano-10-3-(4- 0.1% soln. of the reagent, the mixture was diluted hydroxypiperidino) with HzO to 25 ml and absorbance was measured propyl] phenothiazine} against a reagent blank. For detn. of V in steel, the sample was mixed with the soln. described by Gowda & Achar and treated by the same method. Beer’s law was obeyed over the cited range. Up to 8000 ppm of Fe(III) could be tolerated in the detn. of 3 ppm ofV. N-Phenylbenzo- 475 nm Airborne particulates (5 to 20 mg) were collected hydroxamic add in the filter bag of an air cleaner or the mass- fraction filter attached to an air sampler. The sample was treated with HNOg, H2SC>4 and HC104 to decompose organic matter, followed by H F to decompose suspended residue (e.g. silicates) and the V was extracted as its complex with the reagent into CHC13 for spectrophotometric detn. The calibration graph was rectilinear for 0 to 5 and 0 to 10 fig of V with use of 3 and 5 fil of 0.2% reagent respectively. Up to 1 mg of Mn(II), 3 mg of Fe(IH), 200 fig of Cr(II) and 2 ml of concn. HC104 . did not interfere.

4-Amino-phenol 460 nm Catalytic oxidation of 4-amino-phenol by potassi­ «=925,000 um chlorate and its use in the detn. of V with quinolin-8-ol as activator is studied. To the test soln. containing 0.1 to 1.0 mg of V(V) are added: 10 ml of 5% KCI03 soln., 5 ml of 0.1% reagent in 50% ethanol, 2.5 ml of 3 mM activator and 2-5 ml of 10 mM-NaOH. The mixture is diluted to 25 ml with HgO and, after heating at 60“ on water bath (30 min.), absorbance of the cooled soln. is measured against a reagent blank. Beer’s law is obeyed for 4 to 40 ng/ml of V. CuZ+ and Ti4+ o interfere in 60-fold amounts relative to V. The standard deviation is 0.011 (5 detn.; 95% confidence level) for 0.024 ppm of V(V). o Name of the Reagent PH Remarks Refe. working wavelength withe

N-Phenyl, N-4- 540 nm 6M- To the test soln. (5 ml) are added 5 ml of HaO, 10 :204 chlorophenyl or e=5300 H Q ml of 6M-HQ and 10 ml of a 0.1% of cited reagent N-m-or-p-tolyl- to in CHQ3 and the mixture is shaken for 2 to 5 min; derivatives of 4- e=6900 extn. is repeated with a further 2 ml of reagent amino-or-4-chloro soln. The combined extracts are dried and diluted cinnamohydraxamic acid to 25 ml with CHCI and absorbance of this soln. is 3 measured. Beer’s law is obeyed for 0.5 to 10.0 ppm of V with use of each reagent. The complex is stable for many days and there is no interference from many common ions; large amounts of Ti, Mo and Zr interfere, but these can be masked by adding R (for H ) or oxalate plus F ” before extn.

N2-o-ChlorophenyI- A CHCI3 soln. of I is used to extract V(V) from a 205 N'-hydraxy-N’-m- medium of 1 to 10 M in acetic acid to form a stable tolyl-p-toluamidine (1:2:1) blue violet metal-I-acetic acid complex, and hydrochloride (I) so to detn. 1 to 10 ppm of V. For max. colour, 8- in the presence of fold excess of reagent (relative to V) is needed. In (i) Acetic acid 550 1 to the detn. of 4 ppm of V, there is no interference to 10M- from Cf, B r, N 0 3", SO^2", triethanol­ 570 nm Acetic amine, urea, thiourea, phthalate, borate, citrate, e=4840 Acid tartrate, alkalis, or alkaline earth metals or La; tolerance limits (ppm) for other species are: Pb(II) 1500, Zn(II) or Cd(II) 1200, Co(II) or Th 900, Mn(U) 1000, Ni(U), F e(ni), Ag, Sb(UI), Al, Cr(III) or Ti(III) 800, Nb 80, Ta 100, H (IV ) 60, Mo(VI) 300, W(VI) 2 0 ,1 600, F' 500 and arsenate 400. The method has been used in analysing steel.

(ii) Thiocyanate 590 1 to V(V) reacts with (I) in presence of SON' to form a to 3.5 green ternary (1:2:2) V:I:SCN’ complex which is 500 nm extractable for detection and detn. of V. The limit e=6367 of identification in spot test is 0.1 jug (dilution limit 1 part in 106). The Sandell sensitivity is 7 ng/cm2. Eight- and ten-fold excess of reagent and SCN respectively, are needed for complete extraction. Beer’s law is obeyed for up to 7.2 ppm of V but the optimum analytical range is 0.6 to 6.8 ppm. In the detn. of 4 ppm of V, there is no interference from Cl\ Br, N03\ SO /, P04^, S ^ 2', phthalate, borate, citrate, tartrate, urea, thiourea, alkali, alkaline earth metals or lantanoids. Tolerance levels (ppm) for other species are Zn, Cd, or Hg(II) 1200; Mn(II), Sb(III), or Fe(III) 1000; Cu(II), Ni(II) or A1 800; Cr(III) or U(VI) 600; Mo(VI) 300; Ti(IV) o r Z r 60 and W(VI) 150.

T^’-Dichloro-T 400 nm Z5 Vanadium (V) forms a red complex with cited re­ hydroxyacetophenone to agent at pH 2.5 to 4 and absorbance is measured oxime 4 after extn. of the complex into CHC13; the Sandell sensitivity is 15.3 ng/cm . In detn. of 25 ppm of V o there is no interference from 1000 ppm of acetate, C1‘, Br, r, NOa', S042', B 032', P04 , Zn, Cd, Ba, Ca, or Al; 500 ppm of Hg(II), Ni(II) or Co(II); or 200 ppm of Mo(VI) or Mn(II). Name of the Reagent X or Remarks Refs. m ax. working wavelength withe

Gallacetophenone 390 nm The yellow 1:2 complex formed between V(V) and [2\ 3\ 4'-trihydroxy- «=8600 cited reagent is used for determination of acetophenonejoxime vanadium. Beer’s law is obeyed with 0.5 to 6.0 /xg/ml of V, and the optimum analytical range is 1.0 to 6 pg/ml, the Sandell sensitivity and standard deviation are 5.8 ng/cm2 and 0.019 respectively. Sodium, K, Li, Cd, Mg, Ba, Zn, Pb(II), Mn(II), Cl’, B r, NOg', MnO * and PO^3" do not interfere; but Fe(III), Ti(IV), Zr(IV), Mo(IV), EDTA, oxalate and acetate interfere seriously. In detn. of 4.5 ppm of V tolerance limits (ppm) for other species are A180, Cr(III), 12, W 20, UO,,2* 10, As(III) 70, Co and Ni 10.

Cyclohexane-1,2- 260 nm The test soln. [2 to 50 mg of V(V)] is treated with diaminetetraacetic acid 10 ml of 10 mM soln. of the reagent at pH 5-5. The soln. is made up to 50 ml and absorbance of the (1:1) complex is measured. The method is selective but Cu(ll), Mo(VI), W(VI), Sb(lll), Fe(IlI) and U(VI) interfere when their ratio to V exceeds 1:1. interfere. Zn Cr(VI) and Cu(II) interfere of VC>3", in mediumof 4to 5 M of in VC>3", (II), o ng C and shaken with a 0.1%soln. of reagent in HO Underoptimum conditions V(V) formsa 1:1:1 210 complexwiththe reagent andH O. Beer’sislaw H3P 0 4, beenapplied to the rapid detn. oftrace amountsof obeyed for 0 to 0.8 ppm of v. In a medium of common species can be tolerated.The method has CHQ3. Theorganic phase isseparated, dried over taining 100 HCLAfter min. 10 absorbanceis measured against seriously, but large amounts of Fe(III) and other Vin samples ofsoil, iron, steeland ore. Thecited reagent formsa blue-violet complex on oxidation of7ml of 1% soln. (w/v) toasoln. con­ 212 Mn(II), Zn, Cd, Ti(IV), Mo(VI), U(VI), tartrate, thiourea do notCr(III), Hg(II), CN'and interfere, SCN'do. but Fe(il), Fe(III), in 24 ppm of V(V). Bivalent Co, Ni(II), Pb(II), Na„SO, and diluted to absorbance25 ml with is CHCLmeasured. and There itsfrom is Fe(III),no interference Co(II), but Ce(IV), Ni(II), Mo(VI), Ti(TV)and Cr(III) and Cu(II), citrate, oxalate, EDTA, F'", SO^2’, PO and Thesoln.of V(V), 2 to 8 ppm, madeis 3.5 to 5 M 211 a reagent blank. Beer’s and law 40 is ppm obeyedbut best betweenresults are 2 obtained at 8 and 4 to 3.5 to in H a HO 5M 5 IM­ >1400 e 2-(3,5-Dibromo-2 pyridyIazo)-5- 600 nm <>560000 dimethylamino phenol N-Phenylbutyro- 510nm 2-Aminobenzene thiol- 4-mercaptobenzene 550 nm hydraxamicacid 4-sulphonic[3-amino- sulphonic]acid

107 o® Name of the Reagent X or pH Remarks Refs. working wavelength with e

p-Sulpho benzene 5210 nm 6.5 To the test soln. [containing 25 to 375 fig of V(V)] 213 azo-4-(2^-dihydroxy- were added 5 ml of a 1 mM aq. soln. of the cited pyridine [4-(2^=di- reagent, 5 ml of acetate buffer soln. (pH 6S) and 1 hydraxy-4-pyridylazo) ml of 0.1 M ~ citric acid, and the mixture was dilu­ benzene sulphonic acid] ted to 25 ml with HaO, then heated at 40' to 45' for 5 min. and after 1 hr. absorbance was meas­ ured. Beer’s law was obeyed between 1 to 15 ftg/ml of V and the standard deviation of absorbance was 0.03 unit for 10 samples containing 5 fig of V. The method was applied for detn. of V in steeL

Gallein and sodium 535 nm 4.5 To the test soln. [containing < 34 /rg of V [ were 214 dodecyl sulphate e=16400 added 3.0 ml of 0.2 M-Na-acetate, acetic acid buffer soln. (pH 4.5), 1.0 ml of aq. 2% Na dodecyl sulphate, 1.0 ml o f aq. 1% Na2SOg and 1:5 ml of 1 mM-gallein; the mixture was diluted to 10 ml with H O and absorbance was measured. The calibra- 2 tion graph was rectilinear for 0 to 3.4 ¡ig/mi o f V; Mo(VI) and W(VI) did not interfere. 2-(4-Methyl-l-hydroxy 610 nm 1 mM In a medium of 1 mM to 6M-HC1, that is 0.2 mM 215 phenyl-2-azo)-N- «=10200 to in HaO and 0.09 mM in 1, vanadium (V) forms a methylene basine 6M- V(V-I-fl2Oa (1:1:1) complex. Beer’s law is obeyed {2-[5-(l-methyl-2- HQ for 0.5 to 5 ¿ig/ml of V(V) or V(IV), (which oxidises piperidyl)-2-pyridylazo]- to V(V) during complex formation). Tolerable p-cresol} (I) amounts relative to V (in 2.6 M-HC1) are: Cu 12, with hydrogen peroxide n 4 (if masked with EDTA), Sn(IV) 100, Nb 25 (if masked with F'), Sb(III) 30, Bi or Ni 40 (if masked with EDTA) and Fe(III) 50 (if masked with EDTA); W(VI) and Co interfere. The meth­ od was used for detg. — 5% of V2Og in titano- magnetite ores containing = 2 to 4% of TiC>2, — 30% of FeO and — 60% of FezC>3; samples were initially fused (Na2COg), the metals were dissolved in hot HgO and the ppt. oxides of Fe and H were removed by filtration. The coeff. of variation was <3% (3 to 5 results).

p-Sulphobenzene- 530 nm 5.5 An aq. 1 mM soln. of the cited reagent (5 ml) is 216 azo-4-(2-amino-3- added to a soln. of V (containing 20 to 300ng), in hydroxy pyridine acetate buffer soln. of pH 55, and 1 ml of 0.1 M- (4-(2-amino-3-hydroxy- citric acid is added. The soln. is diluted with HaO 4-pyridyIazo) benzene to 25 ml, heated for 5'min., set aside for 1 hr. and sulphonic acid]. absorbance o f the orange-red complex is measured against a reagent blank. Beer’s law is obeyed and o VO the Sandell sensitivity is 72.4 ng/cm 2. Method is used for determination of vanadium in steels. o Name of the Reagent X ^ or pH Remarks Refs. working wavelength withe

Benzohydroxamic 460 nm 4 Vanadium (V) forms with BHA a yellow complex 217 acid (BHA) and 505 nm 1-5M- at pH 4 o r a red complex in 1J M-HQ, extractable Ammonium HQ into isobutylmethyl ketone. Alternatively a mixed thiocyanate 535 nm 15M- complex is formed with BHA and NH4SCN in 15 HQ M-HQ and absorbance of the extract is measured at 535 nm. The method can be used for detn. of V in steel and rocks if NaF is added to mask interference of Fe and TL

5,5'-Methylene bis 495 nm 2M- Detn. of V in petroleum crude and derivatives is 218 (salicylohydroxamic) <=5100 H Q described by the new method which is rapid and acid four times more sensitive than the ASTM method. . The sample (10 to 30 g) is ashed and the residue is digested with acid, diluted and mixed with 1 mM of ethanolic reagent and the product is acidified to give a red-purple 1:1 complex in 2M-HQ. The absorbance is measured and a rectilinear calibra­ tion graph is obtained for 1 to 12 ppm of V(V). No interference is caused by Ni(II), Fe(II) or Cu(II). Results agreed to within 5% with those of the ASTM, D-1548-63 . (Tungstovanadophosphoric acid) method. 4-(2-Pyridylazo)- 545 mg 12M- Simultaneous detn. of V and Co in biological mate- 219 resorcinol HCI rials by an ion exchange - spectrophotometric method is described. The ash sample =* (0.5 gm) is heated with concn. HC104 (2 ml) and HNOg (4 ml), cone. HP (2 ml) is added and the soln. evaporated to dryness. The residue is evaporated to dryness with cone. HC104 (2 ml) and the product is dissolved in 1 M-HC1 (10 ml); HgO (85 ml) and 2 M-NH4SCN (5 ml) are added. The resulting soln. is applied to a column (3.8 cm x 15 mm) of amberlite CG-400 resin (100 to 200 mesh; SCN form); V is eluted with 12 M-HCI (40 ml) and Co with 2 M-HC104 (50 ml). Each eluate is purified before addition of reagent; the absorbance of Co is measured at 510 nm. The average recoveries of 4 /ig of V and Co are 963 and 98.2% respectively.

Alizarin complexan 500 nm 5-5 Detn. of H(IV), V(IV) and Mn(U) complex with 220 cited reagent is described. The complexes are prepared by mixing a hot soln. of metal ion in ethanol with a hot soln. of reagent in ethanol, and cooling to precipitate the complex. The soln. (pH 5-5) of Ti, V and Mn complexes show max. absorp­ tions, at 525, 500 and 555 nm respectively. Beer’s law is obeyed for up to 71.6, 82.1 and 593 ppm respectively. Optimum range of detn. of Ti, V and Mn are 033 to 30.6 g, 0.93 to 48.4 and 0.20 to 27.7 ppm respectively. i-J Name of the Reagent \nax.or pH Remarks Refs. working wavelength with«

N1 -(4-Chlorophenyl)- 605 nm <2.5 M In the presence of 4-chlorophenol, V(V) reacts 221 N2 -(5-chloro-o-tolyl)- «=7500 acetic with I, to form a deep blue 1:2:1 (V-I-chlorophenol) N -hydroxy-p-toluamidine acid complex which is extractable into CHClg from hydrochloride (I) medium s2.5 M acetic acid. The calibration graph is rectilinear for 0.6 to 6.4 ppm of V, and optimum working range is 1.0 to 5.2 ppm. This method is used for detn. of fig amounts of V in steel containing W.

Bis-(2-Aminophenyl) 590 and 18 N The cited reagent (2% w/v) in acetonitrile reacts 222 disulphide 700 nm HgS04 with V(V) in warm 9M-HgS 0 4 medium, to form a «=1100 deep blue 1:1 complex; a 2:1 ligand-to-metal com­ plex is formed when a large excess of reagent is used. The absorbance is measured in both cases against a reagent blank. Beer’s law is obeyed for 8 to 36 ppm of V, the relative error is 2.72%, and Sandell sensitivity is 46 ng/cm2. The determination can be effected without interference from large excess of Li, Mg, Ca, NH4 , rare earth metals, Al, Ti(IV), Zr, Th, Mo(VI), W(V1), Pt(IV), Rh, Ir, halides, NOg’, P O ^ , ASC^3", oxalate or citrate. In presence of borate a large period of heating is ne­ cessary; Cu, Ni, Co, Pd(II) and tartrate interfere. 6-Amino-5-(2-hydraxy- 500 nm 5 To a soln. containing 6 to 40/tg of V are added 223 phenylazo)-2-mercapto- ascorbic acid, acetate buffer of pH S and 0.1 mM- pyrimidin-4-ol. soln. of the cited reagent; the mixture is diluted with HgO and, after 20 min, the absorbance is measured. The method is used for detn. of V in steel.

4-Sulpho-2-amino- 560 nm 0.24 Vanadium (V) forms a ternary blue-violet (1:1:1) 224 benzene thiol e=1600 to complex with 5 ml of aq. 1% oxalic add and 5 ml of [3-amino-4-mercapto 0.64 1% reagent soln. in concn. range of 0.24 M to 0.64 benzene sulphonic M-HQ M HC1 and absorbance is measured against H?0 add] after 30 min. The complex is stable for 3 hr. Beer’s law is obeyed for 1 to 36 ppm of V(V) and Sandell sensitivity is 30.2 ng/cm2. There is no interference from 50-fold amounts of C0(II), Ni, Mn(II), Sn(II), Pb(II), Zn, Al, Bi(III), Zr, Ta, Mo, W(VQ, U(Vr>, Cr(III), acetate, phosphate, ascorbate, S04 , tartrate, citrate or EDTA, nor from 25-fold amounts of Cu(II), Cd, Re(VII), Ce(IV), Ti(IV) or F \ There is considerable interference from Fe(III) and Grom 25-fold amounts of Hg(II), Pd(ll), Cr(Vl), CN* and SCN".

Molybdophosphate 568 nm A method to determine V in different oxidation states 225 and Rhodamine B [V(V), V(IV) and V(III)J present together has [C l. Basic been given using the d ie d reagents. Beer’s law is violet 10] ( 0 obeyed for S 3 jrg of V(V), and £ 4 jug of V(III) per 25 ml, with V(IV) reduced to V(III). Name of the Reagent Nnax.or PH Remarks Refe working wavelength with«

N-Cinnamoyl-N- 580 nm 0.16M To the sample soln. are added 16 ml of 1% reagent phenylhydroxyl- «=7000 HQ soln. in CHC1,, 5 ml of 2% NH4SCN soln. and amine (N-CPH amine) sufficient CHC13 to maintain the vol. of the orga­ [(N-phenyl cinna- nic phase at 15 ml; acidity is adjusted to be 0.16 M mohydroxamic acid] in HQ. After this extraction the aq. phase is extracted further with two 5 ml portions of C H Q 3, the combined extracts are dried and diluted to 25 ml and absorbance is measured against a reagent blank. Beer’s law is obeyed for 0.4 to 12 /ig/ml of V(V) and the Sandell sensitivity is 7 3 ng/cm . A 50-fold excess of urea o r thiourea is tolerated, and 30-fold excess of Mo(VI) is tolerated in presence of EDTA, but Fe(III), Ti(IV), Nb, and Ta interfere. The method has been applied for analysis of steels and ores.

N-Phenyi benzo- 530 nm 2.8 to Determination of V(V) in plans such as cauliflower, hydraxamic acid «=4950 4 3 M- spinach, alga, fungi and bryophytes is described. A HQ complex is formed between V(V) and cited reagent in the medium of 23 to 43 M-HQ which is extrac­ table into o-dichlorobenzene. Beer’s law is obeyed for 10.6 to 30.0 ppm of V. The relative error is ■& ± 5%. Bivalent Cu, Fe(III), Mg and Zn do not interfere. Phenothiazine 650 nm Z5 To the test soln., containing 5 to 200fig of V(V), 228 e=30,560 are added Na acetate and HO buffer (5 ml) to maintain pH 2.5, 0.1% of reagent soln. (1 ml) in ethanol (8 ml) and H^O up to 25 ml. A green species (stable for 30 min) is formed, and absor­ bance is measured vs. a reagent blank. Ben’s law is obeyed fen- 0.1 to 8 /ig/inl (optimum range 1.4 to 6 3 ftg/ml) and Sandell sensitivity is 1.7 ngfcm . The method is applied for detn. of V in steel

Sodium N-(o-sulphonic 485 4 An orange complex is formed between V(V) and 229 benzoyl)-N -pyridine to cited reagent. Beer’s law is obeyed for 0.2 to 5.8 N-(2-pyridyi)-2- 491 nm 8.5 M- ppm. A 55-fold excess of the reagent is required sulphobenzamide (Na salt) HCI for full colour development The relative error (for 4 ppm of V) is ± 0.8%. For 4 ppm of V, tolerance levels, ppm) for other metals are: Ni 540, Zn 1500, Cu(II) 460, Pd(II) 700, CO 300, Hg(II) 1500, Ce(IV) 1540, A 11200, Fe(II) 6500, Ti(IV) 800, Z r 940, As(III) 1000, Pt 100, Cr(III) 1600, U(IV) 1800 and Mo(VI) 1960.

N-(4-ChlorophenyI)-N- 605 nm 1.7 Vanadium (V) reacts with I and SCN in the pH 230 hydraxy-N'-(23-xytyl) «=6250 to range of 1.7 to 3.0 to give a deep blue V(V)-I-SCN' benzamidine (I) 3.0 (1:2:2) complex extractable into CHQ3. Absorb­ ance of the ext. is measured; the Sandell sensitivity is 8.15 ng/cm2 and Beet's law is obeyed for £7.2 . ppm of V. The reaction is fairly selective and I has been successfully used for detn. of V in steel Name of the Reagent X o r Remarks Refs. m ax . PH working wavelength withe

N-(4-ChlorophenyI) 530 nm 4M- Vanadium (1 to 5 ppm) in Na-hydnsdde soln. is 231 benzohydraxamic HQ used in the Bayer process for extn. of bauxite; it is acid detected photometrically, after extn. into a 0.05% soln. of cited reagent from a medium 4 M in HCL The efficiency of extn. is 96.4 to 99.7%. Phosphate, oxalate, Na, Zn, Ga and A1 do not interfere.

5,7-DichloroquinoIine- 480 nm 1M- A study has been made of the extn. of ternaiy 232 8-ol complexes of V(V) with butanol and qumoline-8-ol H 2S ° 4 or its 5-chloro-or 5,7-dichloro derivatives from HaS04 medium (pH < 2.0) into butanol-benzene (1:1). Only the cited reagent was applicable for extraction > 95% (even from 1 M-HgSC>4) and this compound was used for photometric detn. of V. Beer’s law was obeyed for < 13 ppm. For 4.6 ppm of V, the tolerance limits (mg in 20 ml of soln.) were Cu(II) 0.6; Co(III), Ni(II), Th, Mg or Zn 10; W(VI) or Mn(II) 1.0 and Mo(VI)_03. Iron can be masked at 100-fold levels by PC>4 . In analysis of standard steel, the error was =* 2%.

FIuorene-2,7- 435 nm Acidic To a soln. of V(V), cast iron or steel (10 vol.) were 233 diamine added 10 vol. of As(III) soln. (0.2% of Asg0 3) in H2S 0 4 and 20 voL of a soln. (234.4 mg/ml) of cited reagent in 85% H3P04, and absorbance detn. within 1 hr. Beer’s law is obeyed for 0.2 to 1.4 ppm of V. Interference by NOg' is prevented by addition of urea.

10-Phenanthroline (I) 530 nm 5.6 Spectrophotometric detn. of V in [catalyst] sample 234 with Na-diethyl- containing V(III) and V(IV) is described. The dithiocarbamate (II) sample catalyst (0.1 g) is decomposed by heating and (I) alone 440 nm 7 to with 50% H2SC>4 (30 to 40 ml) and the soln. is di­ 8 luted to 25 ml with HgO. A portion (1 ml) is mixed with 10 ml of 0.1M (I) and (II), and pH raised to 5.6 by 2 M- NaOH; after dilution to 25 ml with HaO the absorbance due to V(III) is measured. Another portion (1 ml) is mixed with ethanol (5 ml) and 10 ml of 0.1 M (I). The pH is raised to 7 to 8 by addition of 2 M-NaOH and after dilution to 25 ml with HgO, the absorbance due to V(IV) is measured. The complex formed with V(III) does not interfere in the pH range used.

N-Phenylbenzo- 530 nm Acidic Determination of V in fuel oil is described. To 235 hydraxamic acid detn. V (0.2 to 15 ppm) the oil is heated with KHS04 and the mixture is evaporated to dryness with H N 03-HC104 (4:1). The residue is dissolved in HC1 and the soln. is treated with 1% K,S O. soln. and shaken with 0.1% of cited reagent in CHC1 : absorbance o f the extract is measured. 3 Chromium, Cu, Co, Bi, Sb and Sn do not interfere and Mo, Zr and Ti can be masked with F’. 0 0 Name of the Reagent X or Remarles Refs. m ax. PH working wavelength withe

N-2-Chlorophenyl 550 nm 3.5 to Samples of e.g. blood, urine or cabbage leaves were 236 cinnamohydroxamic e*6500 7.5 treated with HNOg or HNOa-H S 0 4, soil was acid M -H a fused with Na2SOg in a platinum crucible. A suitable soln.- produced by either method was oxidised with KMnO^ in 3.5 to IS M-HC1; 5 ml of 0.1% of cited reagent in CHC13 was added. The mixture was shaken for 2 min. and absorbance of the dried CHClg extract was measured against a reagent blank. The calibration graph was rectilinear for 0.8 to 7.0 ppm of V. Mo(VI), W(IV) and Zr(IV) interfered. The method was used for determination of V as a pollutant and in steeL

Salicylohydroxamic 440 nm 1M - The sample is ignited at 800’ for 40 min, cooled, 237 ad d h 2s° 4 decomposed with cone. HF, treated twice with cone. HF-H2S04-H20 (2:1:1) by heating to fumes, cooled and dissolved in H20 . The soln. is made 0.5 M in IT SO and treated with 10% NaBF soln. (to mask i f ), 1 M-H2S 0 4 (to maintain the acidity), 0.1 N-KMn04 (to convert V to V(V)) and cited reagent. The complex is extracted (x 2) into heptanol-CCl4 (3:2), the combined organic layers are filtered and diluted to 25 ml with heptanol, and absorbance is measured against a reagent blank. There is no interference from Fe, Al, Ca, Mg, Mo, Cu or Zn in typical soil concn. In determining 8 to 200 ppm of V in soil, the standard deviation was 0.18 to 25 ppm. For <10 ppm of V, the method of addition is used. The limit of detection is 0.5 /ig/ml of V. The content of V is found from a calibration graph. Propan-1,2- 580 Spectrophotometric, polarographic and ampero- diaminetetra- or metric methods based on the complex formation of acetic acid 780 nm V(IV) with cited reagent are described. The calib­ ration graph is rectilinear for 1 to 52 mM-V(lV). The coeff. of variation is <4% for each method.

5-Diethylamino-2- . 540 nm To an acidified soln. (<40 ml) containing 0.1 to 2 (8-quinolyIazo) phenol fig of V(V) were added 5 ml of a 1.8 mM reagent soln. in 10 mM HC1,1 ml of aq. 20% polyoxyethyl- ene-4-(nonylphenyl ether) (20 oxyethylene units) and 3 ml of 0.1 M Tris buffer (pH 7.8). The soln. was heated to b.p. and diluted to 50 ml with HzO; an aliquot was then applied to HPLC on a column (30 cm x 3.9 mm) of ¡i Bondapak CN, with aq. 32% (w/w) acetonitrile containing 5 m mol/kg o f Na acetate and 0.1 m mol/kg of EDTA as mobile phase (1.5 ml/min). The calibration graph was rectilinear for 50 nm to 1 /x M-V and the limit of detection was 8 mM-V (0.4 ppb). Name of the Reagent X or pH Remarks Refs. m ax. working wavelength with e

2-(3t5-Dibromopyridylazo)- 610 nm Vanadium at ppb level in water or soil was detd. as 240 5-diethylaminophenoi- the cited complex. For 30 to 60 ppb of V in H^O, hydroxylamine recoveries were 93 to 98% and coeff. of variation was <3% (n=7); for 0.5 ppm of V in soil recovery was — 91%.

Salicylaldehyde 375 ntn 1M- The sample soln., 15 mi containing 5 to 65 fig of 241 thiosemicarbazone «=4300 Acetic V(V) and 1 ml of 1M acetic acid, is shaken for 2 acid min. with 2 J ml of 10 mM of reagent in butanol and 7.5 ml of butanol. The separated extract is dried over Na_SO. and its absorbance is measured. Beer’s law is obeyed. Appreciable amounts of alka­ li and alkaline earth metals, U(VI), Mn(II), Zn, Fe(HI), Al, N03' and a 0 4*; 4 mg of Se(IV) o r a"; 0.6 mg of Mo(VI); 0.4 mg of Cr(III), citrate, tartrate, or oxalate, 0.1 mg of Cu(II) (in the pre­ sence of and 50 p% o f Ca, Ni, W(VI), H (IV) or Z r are tolerated in the detn. of 50 /tg of V.

Chrome Azurol S 535 nm 2 to Chrome-Azurol S forms a 1:1 complex with V(IV), 242 [CL mordant «=27,300 3.5 of which the absorbance is measured. The reagent Blue 29] is also used to determine metals including Cu, Be, Pd, H , Z r and Fe. Riboflavine 584 nm Determination of V(V), Cr(VI), and persulphate, 243 based on analytical application of the photometric reaction between riboflavine and ethylene diamine- aceticacid, is described. For the detn. of V(V), the sample is treated with EDTA and riboflavine at pH 6 with exposure to 150W light for 10 to 15 min. be­ fore measurements of absorbance. The calibration graph is rectilinear for 20 to 170 ppm. The method is based on the formation of the reducing agent 1,5-dihydroriboflavine. Colourless ions do not interfere in the determination of Cr(VI) or V(V).

Monopotassium sait 575 nm 6.4 The sample soln. containing V(V) 20 to 70 /rg is 244 of phthalomono- treated with a 50 mM soln. of the cited reagent and hydroxamic acid the resulting complex at pH 6.4 (phosphate NaOH buffer) is extracted into 4 mM Aliquot 336 in ben­ zene; after 30 min. the absorbance of the organic phase is measured. Beer’s law is obeyed for 0.25 ppmofV(V).

Pyridoxal 2-pyridyl- 430 nm Acidic In an aq. dimethyl formamide medium in the pre- 245 hydrazone 505 nm Basic sence of KN03, V(V) reacts with cited reagent either under acidic condition (HC1) to form a yellow complex or under basic condition (ammoni- acal buffer of pH 10.0) resulting in a red complex. Beer’s law is obeyed for 0.5 to 4.5 and 0.5 to 3.5 ppm, respectively, for the yellow and red complex. To reduce interference, the red complex is extrac­ ted into isobutyl alcohol or masking agent is used. frJ Name of the Reagent ; \nax.or pH Remarks Refs. working wavelength with e

N-Phenyl cinnamohydro- 590 nm 3 to Vanadium (V) forms a pink complex (soluble in 246 xamic acid and 7M- CHCip with cited reagent, which further reacts Thiocyanate Acetic with SCN~ to form a green complex extractable acid from 3-7 M acetic acid medium into CHC1 , the absorbance of which is measured. Sandell sensiti- +2 vity is 6.8 ng/cm . Beer’s law is obeyed for 0.8 to 6.4 ppm of V(V) and coeff. of variation is 0.55% (10 detn.). Of 40 foreign species tested only Fe(III) and W(VI) interfere seriously.

Phenyl benzimidazolyl- 560 nm 6 to The complexes of Co(II), V(V) and Cu with cited 247 azo-ketoxine-[N-(2- «=57,400 8.2 reagents are described. The reagents I and II form benzimidazolylimino)- ternary complexes with Co(II) and V(V) in aq. benzamidoxime] (I) 10% ethanol containing 20 ppm of I and 80 ppm of - and II at pH 4 to 13 and 6 to 8.2 respectively. The Co 1,10-phenathroline (II) complex exhibits max. absorption at 620 nm («=24,500). Beer’s law is obeyed for 0.04 to 0.4 /tg/ml of Co or V, and S 1000-fold amounts of Al, Ni, Cu, Zn, Bi, Pb, Cd, Fe, Sn, W, Hg o r Ag (relative to Co or V) do not interfere. At pH 7.2 to 10.8, a Cu-I-II complex exhibits max. absorption at 560 nm («=34,900) extractable into CHClg; at pH 4 to 8.6 Co complex is also extd. Beer’s law is obeyed for 0.01 to 100 /ig/ml of Cu. For simul­ taneous detn. of Co, V and Cu in natural water, the sum of Co and V is detd. in 10 ml sample at pH 6 to 8, Co alone is detd. after extn. from a 500 ml sample at pH 7.2 to 10.8 into 5 ml of CHC13- The coeft of variation were <21% (3 or 4 results) when determining — 24 ppm of Cu, 1 ppm of V and 0.6 ppm of Co in natural water.

4-(2-Pyridylazo) 545 nm 1M- A rock sample (0.1 g) is decomposed with H^O^-HF, 248 resorrinol HCI the residue is dissolved in 0.125 M-HgSO^, and diluted to 0.05 M, 0.3% of H_0_ is added and the V adsorbed on to a column of Amberlite CG-400 (S O ^ -form) and then eluted with 1M-HC1-. This soln. is passed through a column of Amberlite CG- 400 (Cf-form) to remove Th and Zr. Vanadium is stripped by elution with 1 M-HC1 and determined. The detection limit is 0.4 ppm.

2-Methyl-4-(l,2,4- 525 nm 8 The cited reagent reacts with V at pH 8-10 (Tris- 249 triazol-3-ylazo) «=25,500 to HC104 buffer) to form a pink violet 1:1 complex in resorcinol 10 aq. 50% ethanol. The colour develops in 15 min, and is stable for at least 2 h. Beer’s law is obeyed for 0.12 to 1.52 ppm of V; the optimum working range is 0.25 to 0.98 ppm. Zn, Cd, A!, Bi(III), Ti(IV), Fe(II) and Fe(IlI) interfere seriously. The method has been applied to soln. of steel from which Fe has been extd. with di­ isopropyl ether. K > Name of the Reagent or Remarks Refs. Xm ax. PH working wavelength withe

Quinolin-8-ol 480 to 3 to An aliquot of a soin, containing Nb,V or Os was 250 500 nm 6.5 treated with 1.5 ml of 0.1 M of cited reagent in aq. 10% acetic acid and the pH adjusted to 6.0 to 9.5, 3.0 to 6 8 or 38 to 6.0 respectively. The soin, was heated to 60*, and naphthaline was added; the mixture was heated till the naphthaline melted, shaken vigorously until the naphthaline solidified, then heated to re-melt the naphthaline, and cooled. Thé naphthaline layer was filtered off, dried and dissolved in CHQ3- The soin, was made up to 10 ml and absorbance measured at 370 to 380 nm for Nb and 400 to 410 nm for Os. Beer’s law is obeyed for 5 to 99.5,38 to 89.0 and 4 8 to 114.0 /tg of Nb, V and Os respectively. The method is applied in detn. of V in steel and Nb in rocks.

N-(4-Chlorophenyl)- 595 nm 0.7 The test soin, is mixed with 5 ml of aq. 2% NaNs 251 N-hydraxy-N'-O-totyl- ««5670 to and adjusted to pH 0.7 to 5 3 and to a vol. of 25 ml, p-toluamidine hydro­ 5 3 then extracted with 10 ml erf 0.1% of (I) in CHCK chloride (I) The extract, plus CHC13 washings (2x5 ml) of the and azide aq. phase, is diluted to 25 ml with CHC1, and the absorbance is measured. The ratio of V, (I) and N ’ in the complex is 1:2:2. The optimum range is 18 to 7.6 ppm of V in final soin. Poly(vinyi pyrrolidone (I) 545 nm To the test soln. of pH 6 to 7, contg. up to 6 fig of Stilbazo [4,4-bis- «=79,000 V(V) are added 2 ml each of phosphate (0.1M- (3,4-dihydroxyphenylazo) KH P 04,0.1M-Na2HPO4) buffer soln. of pH 6.5, stiIbene-2,2'-disulphonic aq. 0.1% of II and aq. 0.1% of I, plus H^O to total add] (II) 50 ml. After 5 min. the absorbance is measured against a reagent blank. The colour is unchanged after 40 min. Beer's law is obeyed. Interference from A1 can be prevented by adding F; prior removal of Fe, Cu, Mo, W, Nb or Sn as sulphide is necessary. Barium, Mg, Ca, Ti, Zr, Cr, Mn, Co, Ni, Zn, Pb and rare earth metals show negligible interference. To determine trace amounts of V in water, the sample (30 to 35 ml) is treated with 1 ml of 0.01M-NagS and 4 ml of 10% Na2COg soln., then filtered; the soln. is adjusted to pH 6 to 7 with HC1,2 ml of 5% NH4F soln. is added and the detn. is completed as above.

Eriochrome cyanine 545 nm The formation of coloured complexes of some ele­ [CL mordant blue 3] «=46,000 ments with I was studied; the V(IV)-I ratio is 1:2. For V, the pH was adjusted to 6.1 with a hexamine soln. and absorbance measured; for others acetate buffer soln. was used. The pH of the test soln. before the addition of I and the buffer should be — 2; the metal/reagent ratio, pH, wavelength and «-value of the complexes were: Cu 1:1, pH 6.4, 535 nm and 22,000; Be 1:1, pH 6.7,525 nm and 36,000; Fe(III) 1:2, pH 6.3,560 nm, 47,000; Pb(II) 1:2, pH 6.4,575 nm and 46,000. N> C\ Name of the Reagent ^max.or pH Remarks Refs. working wavelength withe

o-Dianisidine 450 nm The sample soln. (¿ 5 ml), 1 ml of 10 mM of cited 254 reagent and 3 ml of lM-to-butyl hydroperoxide in acetonitrile, are shaken vigorously at room temp, and absorbance is monitored for 10 min. The method is applied in the detn. of traces of V in high purity organic solvents. The detection limit in acetonitrile is 0.7 ng/ml and the coeft of variation is 4.8%. Cobalt (>40 ng/1) interferes.

N-Hydroxy-N-p-tolyl 610 nm 2.3 A sensitive and selective chromogenic reagent for 255 N-(2-methyl)phenyl- e=6900 to photometric detn. of V(V) in presence of thiocya­ p-toluamidine [N1- 2.7 nate was studied. An aq. soln. of V(V) (100 fig) hydraxy-N2-O-tolyl- was mixed with 5 ml of aq. 2% KSCN, and pH N'adjusted to 2.3-p-totyl-p- adjusted to 2 3 to 2.7 with 2M-HC1 or dil. aq. NHg, toluamidine] hydrochloride the mixture was extracted with 10 ml of a 0.1% reagent soln. in CHC13 for 2 min. The aq. layer was twice washed with 4 ml of CHCIa, the pooled CHC1 extracts dried over Na SO and diluted to 3 2 4 25 ml and absorbance was measured against CHCL as blank. Mn2+, Cu2+, Cr3+, Ni and 44- ^ Zr do not interfere. The method has been applied in the analysis of steel Catechol violet and 67S nm The test soln. was treated with ascorbic acid [to re- 256 Chlorpromazine duce V(V) to V(IV)], hexamine, catechol violet and chlorpromazine. The method could be used to detn. V and Mo(VI) present together; if the pH were reduced to 3.0 by using HQ in place of hexamine, Mo could be detd. alone. The method could be used to detn. Sb(III) also, with measurement at 625 nm and to detn. chlorproma­ zine in pharmaceutical soln.

N-AHA [anthranilo- 470 nm 3.2 The sample of steel, ilmenite or bauxite was treated 257 hydroxamic acid] 595 nm 1.8M- with a soln. of the reagent in isobutyl methyl ke­ or HQ tone at various pH values, and the absorbance of 630 nm 0.95 the organic layer was measured. Calibration graphs were rectilinear in the range 0.2 to 7.5, 0.2 to 6.5 and 0.5 to 12 ppm of V for the orange red, blue, and green complexes, respectively, formed at pH 3.2, in the presence of 1.8 M-HQ and at pH 0.95 respectively.

N-Phenyl-cinnamo- 565 nm lto The test soln. containing 0.02 to 0.15 mg of V(V) 258 hydraxamic add 3M-HQ was diluted to 25 ml and made 1 to 3M in HQ, 5 ml of a 0.2% soln. of the reagent and 10 ml of 1 M- 4-chlorophenol CHQg were added and mixture was shaken for 2 min. The organic phase was dried with = 2 g of Na2SC>4 and diluted to 25 ml before measurement of absorbance. Beer's law was obeyed over the range 0.6 to 7.2 ppm of V. The coeff. of variation (n = 10) was 0.5% for 4 ppm of V. The method was used in analysis of steel. oo Name of the Reagent \nax.or Remarks Refs. working wavelength withe

NN'-dihydroxy- 380 nm The sample soin, containing 14 to 80 fig of V(V) is 259 isophthalamide €=7500 mixed with 10 ml of 4 mM reagent, 3 ml of 0.1 M- orSlOnm NaHCOa (pH 10.8) and HgO to 20 ml; then 10 ml e=5510 of 4.9 mM-methyltriocytyl ammonium chloride in ethyl acetate is added, the mixture is shaken for 15 min and absorbance of the organic phase is measured at either 380 nm (for 14 to 56 /¿g of V) or 510 nm (for 20 to 80 fig of V). The method has been used to detn. V in a standard steel sample.

Chlorsulpho- 600 nm To 1 to 4 ml of the test soin, were added 5 ml of 260: phenol S 1.5% NH^F soin., 10 ml of satd. HgBO soin., 1 ml of 5% ascorbic acid soin, and 5 ml of 2% tartaric acid soin, at pH 3 3 (3 M-HC1 and 8% Na2CC>3 soin.). Then 5 ml of 0.1% reagent soin, in acetone and 5 ml of Na acetate buffer soin. (pH 3.5) were added, diluted up to 50 ml H£0 and absorbance of the blue colour was measured. Vanadium was detd. in 71 alloys, cracking catalyst and dichromate.

Salicylaldéhyde 370 nm Vanadium (V) forms a 1:1 yellow complex with 261 thiosemi- e=6300 cited reagent in aq. medium at pH 5.0 to 6.5 and carbazone 0.5 to 4.0 ppm of V(V) can be determined. Colour remains stable for 3 days and for max. colour development a 5-fold excess of reagent is needed. Sandell sensitivity is 8.09 ng/cm’2. Up to a 100-fold excess of Fe(II), Mn(II)^Mo(VI), F" or SCN and a 200-fold excess of P 0 4 , citrate do not interfere, Co(JI), Ni(II), Cu(II), Fe(II), Cr(III), V(IV), Pd(II), Zn, Cd and Ag do.

Gallic add 415 nm To each of seven std. soln. containing V in the range 262 0 to 80 mg is added 1 ml of 0.035% Hg(NOg)2 soln. After maintaining the mixture for 15 min. at 30±0.2\ 1 ml of 5% (NH^S^-H^C^ is added. Then 1 ml of 1% gallic acid soln. (at 30"C) is added. The resulting mixture is maintained at 30* for 40 min. and absorbance measured immedi­ ately against HgO. The method has been applied for detn. of V in HzO. The limit of detection is 2 ng and the limit of detn. is 0.2 /tg/1.

Salicylohydroxamic 540 nm 0.95 The bluish violet V(V) - I complex, formed at pH 263 add (I) and 3.0, is extd. into isobutyl methyl ketone. It is con­ Thiocyanate (II) verted into a ternary complex by treatment with SCN" (II) at pH 0.95 and is re-extd. into I. Beer’s law is obeyed for 0.4 to 12 ppm of V. Fe(III), Ti(V), Pd(III), Nb(V) and Ta are masked with F" N> and many other species are tolerated. The method VO is applied to analysis of alloy steel and V-bearing ores. Name of the Reagent X or Remarks Refs. m ax. working wavelength w ithe

Uron and Acid 570 nm Detn. of V(III) and V(IV) in aluminium-containing 26(4 Chrome blue K 582 nm glasses is described. The powdered sample is de­ composed by heating with 10 ml each of HF and H2S 0 4 under nitrogen. The soln. is cooled, mured with 80 ml of satd. Ha PO„ 4 soln. and diluted to 100 mi with HzO; an aliquot is transferred to a 50-ml flask containing 5 ml of 10% Tiron soln. and 20 ml of 20% NaBF4, and diluted with buffer (pH 8) to vol;, absorbance is measured and referred to a calibration graph to obtain V(III) concn. Another aliquot is mixed with 20 ml of 20% NaBF4 soln. and with 0.1N-KMnO4 until a faint colour persists, followed by 5 ml of 5% ascorbic acid. The pH is adjusted to 4 with aq. NH3> 3 ml of 0.1% Acid Chrome blue K soln. is added, diluted to 50m ml with buffer soln. (pH 4) and the absorbance is measured and referred to a calibration graph to obtain the total V concn. The limit of detection is 90 fig. Beer’s law is obeyed for < 100 fig of V(II1) or 40 fig of V(IV). 3-(2-Hydraxy-5-methyl 400 nm 8M- Detn. of V(V) with cited reagent is described. The 265 phenyl)-5-(p-methoxy HC1 test soln., containing 100/tg of V, is made 8 M in phenyl) isaxazoline H Q and then shaken with a 5 5 mM of the cited {2-[5(4-methoxy phenyl)- compound In CHOI. Absorbance of the oiganic 4,5-dihydroisoxazol- phase is measured. Beer's law is obeyed for 1.1 to 3-yl]p-cresol} 39.0 fig/ml of V in the final soln. The complex is stable for 60 h. The Sanded sensitivity is 24 ngAan2; the coeft o f variation for 120 fig of V in 10 ml of soln. was 0.95% (n = 15).

3-(2,3-)3-and3- 580 nm 4.5 In these studies it was shown that each reagent re- 266 (4-chloro), 3-(4- acts with VOg+ to form violet 1:1 and 1:2, water bromo)- and 3-(4-iodo- soluble complexes at pH 4.5. Of the compounds phenylazo)-derivatives studied, the 4 halo-derivatives were the most of chromotropic acid suitable for detn. of VOz+. Thus, 2 ml of aq. 1 mM reagent was mixed with a soln. of VC>2 (41.5 to 83.0 /tg) in 1 M HNOa. The mixture was diluted to 10 ml with aq. hexamine buffer (pH 4) and absorbance was measured.

2-Propionyl-naphthal- 430 nm 4.5 The cited reagent forms a 1:1 yellow complex with 267 oxime (a-ethyl-1- to to VOz+ at pH 4.5 to 5 that is suitable for detn. of V hydroxynaphthol 405 nm 5 (2 to 8 ppm). Pud colour develops in 30 min. and dicorime] *=3380 remains stable for 2 hr. Transition metals interfere. The standard deviation for 5 ppm of V is ± 0.0664 ppm. Name of the Reagent ' X or Remarks Refs. m ax. working wavelength withe

9-Salicyl- 530 nm To detn. a 1 ppm of V in niobium pentoxide or ni- 268 fluorone obium pentachloride, Nb is removed by hydrolysis with dil. HgS04 and residual Nb is pptd. with ben­ zene atonic acid. After removing the Nb (and Mo if any present) by filtration, the filtrate is treated with NaOH to adjust the pH to 2.8 to 3 and several drops of 0.02 M -KMn04 are added to oxidised V(IV) to V(V). V(V) is extd. with O.lM-quinolin- 8-oi in CHC1 and re-extd. into ammoniacal buffer 3 soln. of pH 9.4 (to remove Tl, Zr, Sn, Sb and other species). The extract is treated with 5 ml of 0.1M- acetic acid, 0.5 ml of 1% ascorbic acid, 1 ml of 1% gelatin soln., 3 ml of ethanol, 2 ml of ethanolic 2 mM-I and aq. HQ or NaOH to adjust the pH to 4.2 to 4.5 and diluted to 25 ml with HgO. After 1 hr. the absorbance of V(V)-I is measured. The coeff. of variation was <17% (21 to 25 results) for 5.1 to 5.6 ppm of V. l,5-Bis-(5-chloro- . 650 nm Vanadium forms a complex with cited reagent at 269 2-hydroxyphenyl)-3- e=30,000 pH 4 in presence of polysorbate 80. Beer’s law is cyanoformazan and Tween obeyed for s 1.5 ppm of V. The effects of acidity, re­ [polysorbate] 80 agent concn. and temp, and time of reaction were studied. The stability of the complex was detd. 4-(2-pyridylazo) 550 nm 5.8 Vanadium (V) forms a (1:1 complex with I in aq. 270 resorcinol (I) *=37000 40% propanol of pH 5.8 (ammoniacal acetate buffer) contg. 80 ppm of L The lower limit of detn. was 40 ng/ml of V. Tolerable amounts (relative to V) of diverse elements are: Ti(IV) or Mo(VI) 100; Cd, Co or Ni 50; Fe(III) or Cu(Il) 1; Ge, Si, or W(VI) 200; Mn(II), Z r o r Ga 300; Pb, Al, Sb, Cr(III) or Cr(VI) 500; and Th, Zn, Ag or Bi 1000. The method was used for detg. — 19 to 50 /xg/1 of V in effluent (also containing 0.1 to 1 mg/1 of H ) from metallurgical plant. The coeff. of variation was <63% (n=10).

[8,8M>is-(2-HydiT»ty- 620 nm 0.75 V(V) forms a 1:2 complex with the reagent, extrac- 271 phenyliminomethyl)-5, to table into CHCI3; isoamyl alcohol (9:1) from aq. 5'- the melt being extd. with hot aq. ethanol. The aq. soln. is made 4 M in H O and treated with ethanolic 0.1% reagent, then diluted and extd. for spectrophotometric measurement. The relative error is s ± 1.7%. Name of the Reagent : X or Remarks Refs. m ax . working wavelength withe o-Chlorobenzo- 390 nm Reactivity of this reagent towards 48 inorganic 272 hydroxamic acid ions at various pH has been examined, but selecti­ vity and sensitivity were found to be low. For detn. of V(V) a soin, (containing 3Q to 60 is treated with a reagent soin, at pH 3.5; the complex is extd. into a soin, of methyl-trioctylammonium chloride in toluene, and after filtration of organic phase the absorption is measured. The coeff. of variation is 15%.

Azurol S [C.I. Mordant 580 nm The blue temaiy complex formed by V 0S04 with I 273 Blue 29)] (I) and II has a higher absorbance than the complex and Hexadecyltrimethyl obtained with either reagent alone; max. absorb­ ammonium bromide (II) ance was obtained at V 0 2+: 1:11: ratio of 2:1:5 to 1:1:5 and at pH of 3.8 to 4.8. Beer’s law was obeyed for 0.2 to 1.63 /ig/ml of V(IV). No interference reported from minor amounts of other transition metals. Hexadecyl trimethyl 585 nm 5.7 The test soln. 5 ml containing a few/ig of V is 274 ammonium bromide (I) e=66300 treated successively with intermediate mixing with and Eriochrome cyanine 2 ml of Na-acetate trihydrate-acetic acid buffer [C.I. Mordant Blue 3] (II) (pH 5.7), 0.01 g of ascorbic acid, 1 ml of 1% Na2S03 soln. 0.8 ml of 10 mM-I in 20% ethanol, 0.4 ml of ethanolic 10 mM-II and HgO to produce 25 ml. The absorbance of resulting V-I-II (1:3:3) complex is measured against reagent blank; Beer’s law is obeyed for s 18 /ig of V. There is no inter­ ference from £ 5 mg of Mn, Zn, Pb, Ca, Mg, 0.1 mg of W, Mo or Cr, or 0.05 mg of Ni or Co. To de­ termine V in ores, the sample (0.1 to 0.2 g) is fused at 700" with 1 to 2 g of Na2Og in an iron crucible, the cooled melt heated for 10 to 20 min. with 50 ml of hot HgO containing 0.5 ml of 0.02% Na osmate soln. and the cooled soln. is diluted to 100 ml. An aliquot (1 to 5 ml) of the clear liquid is acidified to phenolphthalein with HC1 (1:2) plus a further 1 or 2 drops, then treated with 0.5 ml each of 2% H3BC>3 soln. and 2% NaF soln. In the presence of 1 drop of II indicator sola, the soln. is adjusted with dil. NaOH and HC1 soln. to an orange yellow colour (pH 5.5 to 6.0) and further analysed as above, except that 1 ml of I soln. (instead of 0.8 ml) is used. Results obtained for V (0.14 to 1.15%) in e.g. carbonaceous rocks agree with those obtained u» by the tungsto-vanado sulphate method. Name of the Reagent : ^max.or Remarks Refs. working wavelength withe

Pyrogallol Red (I) 490 nm A rectilinear relationship is observed between the 275 decrease in absorbance of I at fixed times and V(V) concn. over the range 0 to 1.83 ppm at I = 0.1M (acetate buffer) and 25*. The detection limit is 0.05 ppm of V. In the presence of 8.8 mM- KBrOa determinations at ppb level are possible. Effect of 20 different species in ferrous and non- ferrous alloys on the decomposition rate of I in the presence of V(V) has been examined.

To the sample containing 0.015 to 1.273fig of 276 V(V) were added 2.2 M-acetic acid - 0.5 M-Na acetate buffer, 0.11 M-KBrO. and H„0 to 20 ml. Then 0.8 mM of I was added with shaking and the soln. was diluted to 25 ml with HgO; after exactly 5 min. from the addition of I absorbance was measured at 25". The decrease in absorbance of I (0.06 mM) in the presence of KBrOg (4.4 mM) was proportional to the concn. of V in the range 0 to 50.94 ppb and detection limit was 0.61 ppb. The coeff. of variation for five soln. containing 0.41 to 50.94 ppb of V were in the range 5 to 0.4%. There was serious interference from 11, Sn, Mo, Mn(VII), Ce, Cr, W, Al, Sb, Fe, Z r; Nb, Ni, Co, B, Pb, P, As and Mn(II) did not interfere in the oxidation of 0.06 fiM -I at pH 4, whether in the V-KBr03-I or the V-I system.

Eriochrome cyanine R 575 nm 33 The optimum condition of the formation of 277 (CL Mordant Blue 3) (I) «=79000 to ternaty complexes of V(IV) with I, II or III in Chrome Azurol S 53 presence of IV have been detd. The complexes (CL Mordant Blue 29) (II) were formed at pH 3.5 to 5.5. The most useful for or Catechol Violet (III) detn. of V was that with I and IL The procedure for in presence of Zephiramine, detn. of V in steel by formation of this complex is hexadecyltrimethyl ammonium described. o r hexadecylpyridinium ions (IV)

Prochlorperazine bis 529 nm 10M- The sample (0.5 g) was gently boiled with mixture 278 of 15 ml of 5M-H2S04, 2 ml of concn. HgP 04 and (methansulphonate) H 3 P ° 4 1 ml of concn. HNO . then cooled and diluted to 3 50 ml and aq. KMnO^ was added slowly [to oxidize V(IV) to V(V)]. After 5 min. aq. oxalic add was added until the pink colour disappeared, and the product was diluted to 100 ml. To a portion of this were added Na citrate (40 mg), lOM-HgPO^ (123 ml) and 2 ml of aq. 0.1% reagent; the mixture was diluted to 25 ml and absorbance was measured against a reagent blank. V (2 3 to 155 fig) was detd. bom a rectilinear graph. The most interfering spedes were f (0.1 ppm), Pt(IV) (20 ppm) and Rh(III) (45 ppm). The method has been applied to determine V in steels contg. Cr, Mo, Mg, Ni and Cu. oo Name of the Reagent \naic ^ Remarks . Reb. working wavelength with*

1,10-Phenanthroline (I) 650 nm 6 to The method has been improved by making the reac- 279 Bromophenol Blue (II) «*53000 7 tion mixture of V(IV) with I and II, forming the Hexadecylpyridinium (III) ternary complex, 0.16 mM in the surfactant (III). The absorbance of this four-component complex is meas­ ured and Beer’s law is'obeyed for 0.2 to 12 /ig/ml of V(IV) at pH of 6 to 7. The reagents have also been used for determination of Co(II) at 640 nm.

2- (3,5-Dibromo-2- 640 nm 2.8 Within the concn. range 0.05 to 0.5 ppm, V(V) 280 pyridylazo)-5- reacts with this reagent at pH 2.8 (KH phthalate- dimethylamino- HC1 buffer) in acetone to produce a stable blue benzoic acid coloured complex. The calibrated graph is recti­ linear and the coeft of variation (n=20) for 6/rg of V is 1.2%. Co2+, Cu2+, Fe2+, Ni2+ and Pd2+ interfere. The method is applied for detn. of V in fuel oil and stock gas.

3- (2-Hydroxyphenyl)- 430 nm 2 The cited reagent was also used for Ti(IV) at pH 281 1-phenyl triazene-1- «=14010 2.5 (430 nm, «=11970) and Mo(VI) at pH 2 (440 oxide nm, «=6764). The 1:2 complexes formed are ex­ tracted into benzene for absorbance measurement. The effect of several foreign species is described. TMBHA [4-Methaxy-N- 580 nm The V(V) reacts with TMBHA in presence of 282 (m-tolyl)benzo- «=7100±50 NH^SCN to give an intensely coloured complex hydroxamic acid] and which is extractable into CHC1 ; absorbance of the 3 Thiocyanate «tract is measured and Beer's law obeyed for up to 4.8 ppm of V, with a coeff. of variation of 0.59%. Mo(V), W(VI), Zr(IV) and Fe(UI) did not inter­ fere. Between 500 ppm and 2% of V was detd. in steel and ore samples. Blood, urine and plant material were also analysed successfully.

4-(2-Thiazolylazo)- 550 nm A 0.5 g sample was dissolved in HNC>3 + hydrated 283 resorcinol «=20,360 tungstic acid (1:1), was filtered off & oxidised. Nitrogen was removed by boiling. Most of the Fe was then extd. into isopropyl ether, and Cr and Mn in the acid layer were oxidized by boiling with KC104- Fe and V were pptd. by aq. 50% NHg, the ppt. was dissolved in 1:5 HC1 and Fe in the soln. was masked with NH4F. An aliquot (0.2 to 2.0 ml) of this soln. was treated with 2 ml of aq. borate buffer (pH 9.2), 0.4 ml of aq. reagent and 1 ml of lM-hydroxylammonium chloride, diluted to 10 ml, heated on water bath for 5 to 10 min., cooled and absorbance was measured. Beer’s law was obeyed for 0.1 to 1.0 /ig/ml of V and the Sandell sensitivity was 2.5 ng/cm . Fe, Co(Il), Ni(II), Cu(II), Pb(II) and EDTA interfered seriously; oxalate, tartrate, acetate, P O ^, F \ Mn(II), Ba and W(VI) could be tolerated in large amounts. Method used for detn. of Vin steel. Name of the Reagent \nax. °r pH Remarks Refs working wavelength withe

Molybdophosphate- 570 nm Acidic Vanadium molybdophosphate reacts with Nile Nile blue (CL e=1.3xl0'5 blue to give 1:4 complex which is dissolved in water Basic Blue 12) to give a blue soln. A soln. of mixed acid (oxalic- tartaric-HgSOp is added to decompose excess of molybdophosphate before the colour reagent is added. Beer’s law is obeyed up to a Vg0 5 concn. of 0.2 /ig/ml. The coefficient of variation was 3 to 8%. Micro amounts of V in minerals can be detd. without separation.

4-(2-Pyri2, evaporated to dryness and the Tetrazolium chloride (II) residue is heated to dryness with two further 5-ml portions of concn. HNOg. The final residue is dissolved by heating with 5 ml of concn. H N 03 and 30 ml of H O , the soln. diluted with H O . An aliquot (2 to 5 ml) is mixed with 10 ml of propanol, 0.5 ml of 0.4 mM 1,0.5 ml of 10 mM II and 10 ml of ammoniacal acetate buffer soln. containing 40% of propanol (pH 5.8). The V complex is extd. into CHClg (2x5 ml) and absorbance of the combined extracts is measured vs. a reagent blank. 3-[4~(5-Bn>iiio-2- 589 nm To the sample soln. (containing =* 5/igofV(V)] 286 pyridyiazo)-3-hydraxy- were added 1.1 ml of 0.5M-H2SO4, 1 ml of 0.4% N-propyi-anilino] propone KIC>4 soln. and 0.4 ml of 0.05M-cyclohexane-l,2- sulphonicadd diamlnetetra-acetic acid (to inhibit interfering ion). The pH was adjusted to 4.5 with 1 ml of 2M- Na acetate and 0.4 ml of 5 mM-reagent was added. The ml. was made up to 10 ml with H£0 and absorbance was measured. Only Co(II) and U(VI) interfered seriously. 5,7-di-Iodo- 400 nm A soln. containing 0.1 mM-V(V) (12 ml) was 287 quinolin-8-ol «=7700 added to 2 ml of 0.01M reagent and pH before dilution to 20 ml was adjusted to 3.5. Then 2 ml of 30% H .O . was added and the mixture was extd. with butanol-benzene (1:1), the absorbance of the dried organic phase was measured. Beer’s law was obeyed for S 12 pg/ml of V. The optimum range of analysis was 1 to 6fig/mL Oxalate, tartrate, citrate, PO^, EDTA, Co(lI), Mn(II) and Mo(VI) interfered. The method is used for analysis of a liq. pharmaceutical formula. 2'-Hydroxy-4- 630 nm The sample containing — 300p,g of V(V) was aci- 288 methoxy-5’-methyl- diSed to 9M-HC1 and extd. with a CH O a soln. of chalcone oxime (HMMCO) the reagent. The absorbance of the green CHG3 ext. was measured and Beer’s law was obeyed for up to 94 pg/ml of V. For detn. of V in binary mixtures with Nb, Ta, or H, relative errors were up to ± 1.8% with coeff. of variation — 0.36%. The method was also applied to samples of bauxite and magnetite containing 0.1 to 1% of V. Name of the Reagent X o r PH Remarks Refs. m ax. working wavelength withe

Salicylohydraxamicacid 392 or 9.2 The soln. of V(V} (15 to 75 fig) is treated with an 289 585 nm aq. soln. of the reagent and buffered at pH 9.2 (NH -NH4C1); the mixture is then made up to vol. with H O and extd. for 15 min. with a 6 mM soln. 2 of methyltrioctyl ammonium chloride in toluene and absorbance of the organic phase is measured.

Acid chrome blue K. (I) 590 nm 4.2 to Solvent extn. and photometric detn. of V in A1 is 290 4 3 described. The sample (5 g) is fused with H3BOa (5 g) and NagC 0 3 (10 g) at 1000" for 15 min. The melt is leached with hot HgO, filtered and diluted to 100 ml with H20 . To a 10 ml aliquot are added 2 or 3 drops of a 0.1% soln. of thymol blue and IM­ H O to give a pH of 2 to 3. Several drops of 0.05M- KMn04 and 10 ml of a satd. soln. of benzoin «- oxime in CHC13 are added and after 2 min, the organic phase is removed. The aq. phase is extd. again with 10 ml of C H G g. The combined extracts are treated with 20 ml of O.Q2M-NaOH and after 1 min. the aq. layer is filtered and the organic layer is again extd. with 10 ml of 0.02M-NaOH. To the combined aq. extracts are added 5 ml of 3% ascorbic acid soln., 10 ml of 10% NaBF4 soln., 10 ml of 10% tartaric acid soln. and 3 ml o f 20 mM 1. The pH is adjusted to 4 with 1 M-HC1 and the soln. is diluted with acetate buffer soln. (pH 4.2 to 43). After 40 min. the absorbance is measured.

4-Benzoyl-3-methyl-l- 475 nm 'T h e V(V) reacts with I in ethanol-CHCl -HaO phenylpyrazolin-5-one «=1910 (7:2:1) of pH 2.5 to 4 containing 2 mM-I to form a V(IV)-I (1:2) complex ¡V(V) is reduced to V(IV) during complex formation). Beer’s law is obeyed for 0.6 to 20 figfint of V. Tolerable amounts of diverse metals (relative to V) were: Co (500), Cr(III) and Ni (200), Mo(VI) (20), Cu (5) and H(IV) and Zr (2); Ge and Nb did not interfere but Fe(HI) did. The method was used for detn. of = 9 to 68% of V in V-Ge or V-Ge-Nb superconductor alloys, and could also be used for detg. — 50 to 100 fig/ml of V(V) by difference spectrophoto­ metry. The coeff. of variation were < 4% (n=3).

Tartaric arid 375 nm The neutral sample soln. containing 0.1 to 1 mg of V(V) was mixed with aq. 1% reagent and the pH adjusted to 2 to 3; after extn. with a 1% soln. of trihexylamine in CHC13, absorbance of the extract was measured. Sample soln. containing Cr(VI) were first reduced in a 0^M-HgSO4 medium with 5% NagS03 soln. until the green colour of Cr(IlI) was obtained, followed by removal of the excess of reductant. Platinum and Pd interfere seriously as well as Mo and W in amounts of >1 mg; Ti(V) forms a ppt. and Zr, Sn and Sb become hydrolysed, thus hindering the phase separation. Name of the Reagent X^^ or pH Remarks Refs. working wavelength with e

W-Bipyridyl 220,225 10.36 Spectrophotometricdetn.ofV(V), Nb(V)and 293 or250nm Ta(V) in presence of each other and other interfering ions by cited reagent is described. Niobium (V) was adjusted to pH 3.9 and detd. at 230, 235 or 275 nm and Ta to pH 10.05 and detd. at 210, 225 o r 250 nm depending on the matrix. Many ions interfered. N-Hydroxy-N-Phenyl- 600 1 The sample soln. was adjusted to pH 1 to 3.5 with 294 N'-p-chlorophenyl-o- and to , 2M-HC1, a 1% soln. of KSCN (5 ml) was added chlorobenzamidine 620 nm 3 J and voL adjusted to 25 ml. The mixture was extd. hydrochloride [2- with a 0.1% soln. of the cited reagent in CHQ3 (25 chloro-N2 -4-chloro- ml) and absorbance was measured. The response phenyl-N1 -hydroxy-N1 - was rectilinear for 20 to 240¿ig of V. Tolerance phenyl benzamidinium- levels for various ions (in ppm) were; A1 (2700), chloride] and thiocyanate Zn, Cd and Cr (2000), Fe (1700), Mn (700), Ni and Co (600), Cu and Mo (250), 2 r (200) and W (20). The method was applied to analysis of three stand, steels.

Decan-1,10-di- 445 nm 2 to The cited reagent forms a complex with V(V) at 295 hydroxamic acid e=27,000 3 pH 2 to 3, which can be extracted into CHClg and absorbance of the ext. can be measured for which Beer’s law is obeyed. The effect of pH range and diverse ions is discussed. Thymolphthalexone 600 nm 3 Spectrophotometric detn. of V(V) and Mo(V) in 296 alloys and steels is described. For V the alloy sample is decomposed with acid and the soin. is mixed with 3 mi o f 3% NaF soln.; sufficient aq. 10% NHa is added to raise the pH to 2 to 25, and also 10 ml of acetone (of pH 2 5 with H Q ); the V(V) is completed with 1 ml of 1% reagent soln., acetate buffer soln. of pH 3 is added to make the vol. 25 ml, and absorbance is measured against H20 . Molybdenum forms a complex with the same reagent and its absorbance was measured at 364 nm against HaO. In these methods separation of accompanying metals is not necessary and they are rapid.

Hexadecyi pyridinium 610 nm 3.8 The sample (containing 4.5 to 60 ¿tg of V) was 297 or62Snm mixed with 6 ml of a ImM soln. of one of five or630nm alizarin dyes, 5 ml of 0.1 M acetate buffer (pH 3.8) and 10 ml of 10 mM-reagent. The mixture was dilu­ ted to 50 ml; after 30 min. the absorbance was measured.

4,5-Dibromophenyi S67nm 4.9 Vanadium forms a ternary complex V(V)-I-II 298 fluorone (I) «=102,000 to (1:1:2) in the presence of Triton X-100 at pH 4.9 and Hexadecyltrimethyl- ¿2 to 6.2. Beer’s law is obeyed for 0 to 7 fig of V(IV) ammonium bromide (II) in 10 ml of soln., Fe(III), Ti(IV), In, Ta(V), Ge and Ga interfere seriously. The reagent I can be used to determine traces of V(IV) in silica, soil and water after separation of the interfering ions. Name of the Reagent X. o r PH Remarks R e f s . m ax. working wavelength with e

SCN" 395 nm Acidic To detn. tervalent V the ore sample is dissolved by 299 5 ml each of 5M-H2S04 and cone. HF, and heated in a PTFE-lined bomb at 100* for 3 h. in a vacuum oven. V(III) is detd. in presence of V(IV) by formation of V(III)-SCN" complex in aq. acetone medium. The calibration graph is rectilinear up to 50 p.M and detection limit is 0.5 ¿iM. Interference by Fe(III)-SCN" complex is removed by addition of SnCl . The method was tested on a vanadiferous 2 mica, rescoelite, and on vanadium oxide minerals.

Thiophene-2- 410 nm 2 A sample soln. containing 12.25 to 125 fig of V was 300 hydrazide [2- «=12100 mixed with 5 ml of a 03% soln. o f the reagent in theno-hydrazide] aq. 40% ethanol, 3 ml of buffer soln. (pH 2) and HgO to 25 ml. The absorbance of the yellow (1:1) water soluble complex was measured. Beer’s law was obeyed for up to 125 /ig of V. The relative error and coeff. of variation for 123, 62.5 and 125.0 fig of V (each n=5) were +4.0% and 0.8%, +1.0% and 0.5%, and -0.6% and 03%, respective­ ly. Interference of 33 foreign species is reported. N-Hydraxy-N-m-tolyi 570 nm 1.0 to The V(V) forms with this reagent a 1:2 complex 301 N1-phenyl benzamidine <=4140±50 10.0M- which is extractable into CHC13 in 1.0 to 10.0 M- Acetic acetic add medium; the absorbance of the extract add is measured. Beer's law is obeyed feu- 0.8 to 12.0 ppm of V,and thecoeff. of variation is 0.61% for4 ppm. The method was used to determine V in steel. Diantipyrinyl- 500 nm Addic Conditions have been studied for the detn. of trace 302 styrylmethane 150,000 of V in ores with cited reagent in inorganic adds. [3,3-diantipyrinyl- The apparent e value at 500 nm increases from 1- phenylprop-l- 53,000 to 150,000 in the presence of Mn(II). Beer’s ene] in presence of law is obeyed over the range 0 to 03/rg/ml of V. manganese (IQ The effect of foreign spedes has been investigated.

2- Pyrilidenimino- 487 nm 2.6 Two methods for spectrophotometric detn. of 303 benzo hydraxamic and V(V) with cited reagent are proposed. In the first, [2-{2-pyridyl methylene 485 nm 10 ml of ethanolic 7.4 mM-I, a soln. containing 3 to amino) benzohydnnamic] 8 ppm of V and 5 mi of chtoro-acetic add-Na acid (I) acetate buffer, pH 2.6, were mixed and made up to 25 mi with H^O and absorbance measured against HzO. In the second procedure, 5 mi of aq. 6 mM-I, a soln. containing 0.6 to 1.6 ppm of V(V) and 5 ml of buffer soln. were made up to 50 ml with HaO and shaken vigorously for 3 min. with 10 ml of iso­ amyl alcohol. The separated organic phase was dried with Na SO, and absorbance was measured against H^O. The methods were applied to the detn. of V in steel. 00 Name of the Reagent k or Remarks Refs. m ax. PH working wavelength withe

Ethylisobutrazine 518 Acidic Stock soln. containing 2.5 to 155 fig of V(V) was 304 [etymemazine] hydrochloride e=9750 mixed in 3.5 to 6.5M-H PO medium with a 0.1% 3 4 soln. of the reagent. The absorbance of the ext. was measured and Beer’s law was obeyed in the range 0.1 to 6.2 ppm of V(V) with an optimum concn. range of 0.4 to 6.0 ppm. The effect of pH, time and temperature and concn. are reported. Fe(II), ; Ce(rV) and Cr(VI) interfered seriously. Method has been used to determine vanadium in ilmenite and vanadium steels.

3-(Picolydene) 395 nm Acidic Spectrophotometric detn. of binary mixtures of 305 benzenesulphonic arid Ni(II), Co(III) and V(V) was studied. The cited re­ [<*-(3-sulphophenyl) agent, which was stable in aq. media, reacted with picolinaldehyde 2-hydroxy- Ni(II), Co(III) or V(V) in slightly acidic soln. to benzoyl] hydrazone form coloured complexes with absorption max. at 375 and 385, 400 and 415 for Ni(II) and Co(III) respectively. The e values ranged from 14,000 to 36,000. Simultaneous detn. of 1 mg/1 of Ni or Co and 2 mg/1 of V in acetate buffer soln. was possible, without interference from Hg, Pd, Pt, Cr(III), Sn(II) or citrate; Zn, Bi, Cu(II), Fe, In, Ti and S* did interfere. N-(4-Chlorophenyf) 530 nm 4M- The selective extn. of V(V), in the presence of benzo hydroxamic add HQ CrQlI), Mo and Fe(III), from 4M-HCI into CHC13 with this reagent has been used for detn. of 2 to 5 pg/ml of V. The standard chromium hot-die steel samples (0.02 to 0.5 g) were brought into soln. by two methods (i) the steel was dissolved in 25% HgS04, boiled with concn. HNOa until brown fumes ceased, diluted with HzO, then boiled, and treated with standard KMn04 soln. until a per­ manent pink colour or ppt persisted. The soln. was again boiled for 5 min., filtered and diluted, (ii) The steel sample was heated successively with two portions of 50% H Q , followed by heating with cone. HN03. The soln. was filtered, the residue was ignited and fused with Na2COg and HgB 03 in a Pt crucible; the ext. of the melt in H Q was mixed with filtrate and the soln. was diluted for analysis. The error was between 1.03 and 4.5%, coeff. of variation were between 2.057 and 9.109% for all the samples. Carbon, Si and S had no effect on the detn.

Gallic add 415 nm For detn. of Mo and V, the foodstuff is destroyed with H_SO by a wet-oxidation procedure. Mo in an aliquot of 2 4 the digest soln. is extd. as its toluene-3,4-dithiol complex into isoamyl acetate and measured at 680 nm. V is detd. directly in a smaller aliquot by its catalytic effect on the oxidation of gallic arid with H2S04 and absorbance is measured. The detection limits are 0.023 ppm of Mo and 0.015 ppm of V. Name of the Reagent \nax.or Remarks Refs. working wavelength withe

Di-2-Pyridyl _ 572 nm The sample soln., containing < 15 fig of V(V), was 308 [ketone] 2-quinoIyl- applied to a column (6 cm x 9 mm) of Dowex 50W- hydrazone (I) X8 (50 to 100 mesh) elution being effected with 20 ml of 0.1M-HNO3 containing 1% of H2Og. The eluate was evaporated to dryness, 1 ml of 1M- NaOH and 2 ml of aq. 0.3% Br were added and the soln. was evaporated. The residue was treated with = 10 ml of HgO and 1 ml of 1M-HC1, 0.5 ml of aq. 1% phenol and 2 ml of aq. acetate buffer (pH 3.5) were added. After dilution to' 20 ml with HzO the mixture was extracted (for 30 min.) with 10 ml of this reagent in CHC13 and absorbance of the extract was measured. Beer’s law was obeyed for up to 1.5 ¿ig/ml of V. The method was applied to detn. V in three standard alloy steels.

Sodium 5-(4- 540 nm fhe sample soln. [0.5 to 45 fig of V(V)] was 309' diethylamino-2- e=36500 treated with 5 ml of Na acetate-HCl buffer soln. hydroxyphenylazo)- (pH 3.90) and 5 ml of a 0.02% soln. of SATC and l,2,4-triazoIe-3- was diluted to 25 ml with HaO, and absorbance carboxylate (SATC) was measured within 60 min. Beer’s law was obeyed for 0.02 to 1.8 ppm of V(V). The reaction was insensitive to temp. (10° to 72"). 4-(2-Pyridylazo) 560 nm 5 The samples of diy plant material such as carrot, resorcinol (I) potatoes and flour were mineralized with HNOg and Zephiramine (II) and HC104, the residue was heated to dryness with 60% HCIO, then treated with concn. H SO, and concn. HNOa. After evaporation of the add the residue was mixed with HgO then 2M-NaOH was added in small portions until the pH was 10 to 12. The mixture was heated for lh, cooled, acidified to pH 6 with dil HC1 and mixed with O.lM-trans- cyclohexane-l,2-diaminetetra acetic acid, then acetate buffer soln. (pH 5) and 2 mM [of (I)] were added; the mixture was extd. with portions o f 37.5 mM-(II) in CHQg. The combined exts. were diluted with CHC13, filtered and absorbance was measured, referred to a calibration graph prepared for 0 to 0.5 jig/ml of V. The coeff. of variation were 12 to 24% (n = 8 to 16).

Benzohydrmamic 485 nm 2.5 Determination of V(V) and Mn(II) is described. acid

E.C. 1,2,3,2- 340 nm 7.4 Vanadium in 0.05M-tris-HN03 buffer (pH 7.4) 312 Xanthine oxidase was mixed with a soln. containing xanthine NADH, AgNOa and dithioerythritol. The change in xanthine oxidase absorbance was measured against time. The calibration graph was rectilinear for 0.5 to 10 /iM-V and the coeff. of variation was £ 2.2%. Interference was observed from Cu, Mn(II)andNi.

Carminicacid (I) 570 nm 4.8 The sample containing = 1 mg of V was fused 313 and Hexadecyltrimethyl- with N a O . the metal was dissolved in hot H O , ammonium chloride (II) and the excess of NagOa was decomposed by boil- . ing for 10 min. The cold soln. was diluted to 250 ml with HgO, and a portion of the soln. containing = 20 fig of V was neutralized with HgS04 (1:3) and mixed with aq. 4% N aF (0.25 ml) and reagent soln. [acetate buffer (pH 4.8)~2 mM-(I), 0.01 M-(II) and aq. 5% ascorbic acid (10:4:5:2)] (10.5 ml). The mixture was diluted to 25 ml with H O ; after 15 min, the absorbance of the soln. was measured against reagent blank. Beer’s law was obeyed for 0.01 to 0.05 mg of V in the final soln. The method is applicable in detn. of V in metallurgical samples. N-Phenyl cinnamo- 440 nm 1.5 Simultaneous determination of Fe(III) and V(V) 314 hydroxamic acid (I) «=7720 to with cited reagents is described. A mixture of test and Thiocyanate 580 nm 2 soln. (containing 25 to 175 fig of Fe(III) or V(V) «=7750 o r both), 5 ml of O^M-NH^SCN and HgO to 25 ml was adjusted to pH 15 to 2 with 1M-HC1 or 1M- NH3 and the resulting soln. was extd. for 2 to 3 min. with 10 ml of 5 mM-I in toluene. The organic phase was dried over Na^O^ (2 g) and diluted to 25 ml with toluene and the absorbance was measured against a reagent blank. The Fe(III) and V(V) concn. were calculated by means of simultaneous eqn., the « values at 440 and 580 nm being 8200 and 800 for Fe(III). Beer’s law was obeyed for 0.6 to 7.2 mg/I of Fe(III) (optimum range 15 to 6.0 mg/1) at 440 nm and for 0.6 to 8.0 mg/1 of V(V) (optimum range 1.8 to 6.2 mg/I) at 580 nm. Tolerance limits are listed for > 40 foreign ions. For 5 mg'! of Fe(III) or 1 mg/1 of V(V) the coeff. of variation were 0.4 and 0.6% respectively (n=10).

o-Phenylene diamine (I) 440 nm 3.2 Water samp le is mixed with I, KBrC>3 and Tiron at 315 pH 3.2 that have been pre-mixed; the resulting . soln. is passed through a reaction coil (2.25 m) at 25" before measuring its absorbance. V catalyses the oxidation of I by BrC>3 and Tiron acts as activator and as masking agent for foreign ions. ow ui The coeff. of variation (n=15) was 0.37%. Recovery was >96%. Name of the Reagent X or pH Remarks Refs. working wavelength withe

2-(5-Bromo-2- 590 nm 2 Inabu£fermediumofpH2to3(monochloro 316 pyridylazo)aa-5- e*90,600 to acetic add Na-acetate), V forms a 1:1 complex diethylaminophenol 3 - with dted reagent which can be dissolved in a surfactant (8176). The calibration graph is rectilinear for 0.2 to 16 fig of V in 25 ml of final soln. The method was applied to determine trace amounts of V in ores. Chlorpromazine 525 nm The method is based on catalytic effect of Von the 317 oxidation of d ted reagent by KBrO . followed by kinetic measurement of the absorbance. The concn. range is 10 to 400 ng/ml and the coeff. of variation is 4.97% at the 2.4 fig level (n=10). Petroleum products are analysed using this method. 2-Aminobenzo- 550 nm 9.5 The complex with V(V) is extd. from aq. soln. con- 318 hydroxamic ad d taining NH^NH^Cl buffer (pH 9.5) into Adogen 464 soln. in toluene; the organic phase is separated, dried and its absorbance is measured. The calibration graph is rectilinear from 0.2 to 2.2 ppm of V with an optimum concn. range of 0.4 to 1.8 ppm and relative error of 12% (95% confidence) at level of 0.9 ppm. Most foreign ions do not interfere. The method is applied to the dein. of V in crude oil and petroleum fractions. Methyl-2-pyridyl 400 nm 3.5 Mix the sample soln. with 2 ml of 5 mM reagent, 319 ketone thiosemicarbazone £=5600 adjust the pH to 3-5, dilute to 25 ml with phthalate buffer soln. and measure the absorbance against a reagent blank. Beer's law is obeyed for up to 8 ppm of V(V) in the final soln. Sandell’s sensitivity is 9 ng/cm2. Calcium, Re(IV), Se(IV), EDTA, oxalate, F and citrate interfere seriously. Salicylic acid 620 nm Acidic The sample soln. containing 2.0 to 3.2 fig/ml of V 320 was treated with 10 ml of 0.1 M reagent in formic acid; the mixture was made up to 25 ml with formic acid and the absorbance of the unstable blue complex was immediately read. Stability was independent of pH, temp, and presence of light. No interference was observed from common ions up to 0.1%. Interference by Ti(lV), Mo(Vl), Cu(II) and Cr(III) was observed at concn. > 0.03, 0.05,0.02 and 0.05% in soln. respectively.

Phenyl fluorone 520 n o 4 In aq. = 75% ethanol (10 ml) of pH 4 containing 321 «= 2 1 ,0 0 0 2 ml, soln. of the reagent (0.32 mg/ml) a 1:1 complex is formed with V(V). Beef’s law is obeyed for 2 to 25 fig of V(V). The sensitivity is 0.48 fig/ml per 0.001 absorbance unit. The coeff. of variation • is 2%. There is no interference from a 1000-fold excess of Na, K, Cu, Sr, Ba, Mg, Zn, Cd, Hg2+, Co2+, Ni and Cr3+ and a 10-fold excess of AsOv", FeZ+, Fe3+, Bi3+ and Mn2+; but Sn4+, Sn2+, Sb3*, Ti4+, Pb2+, Ga3+, Mo6+, We+, Nb5+ and Taa+ interfere seriously. Ut C\ Name of the Reagent pH Remarks Rets. Xmax. or working wavelength withe

5-Amino-2-(2-quino- 565 nm 2 to A (1:2) complex is formed with V(V) in aq. 322 lylazo) phenol e=40,300 4 medium of pH 2 to 4 (acetate buffer soln.) con­ taining more than a two-fold molar excess of the reagent relative to V. Beer’s law is obeyed for — 0.03 to 2 /tg/ml of V(V). Tolerable amounts of diverse ion (relative to V) are: A1200, Ba, Ina, As, Sb, or F1-100; H f and Mg 80, W(VI) 45; Ge and Be 25; Cr and Ag 20; Mo(VI) 10; Th 4; Sn and Fe(III) 6; Zn 1; Z r and Ti 30; Ni 9 and Bi 40; Ca, Ga, Sr and U(VT) do not interfere. The method is used for determination of — 12% of V in steel; the coeff. of variation is < Z4% (n=3). Quinoline-8-ol (I) 530 nm 3.2 To < 40/ig ofV in acidic soln. are added 5 ml of 323 TritonX-100 soln. (2 g/ml) and 2.0 ml of 96 mM reagent. The pH is adjusted to 3.2 with Na acetate and the mixture is diluted to 20 ml with H O, 2 heated for 10 min. at 60 . cooled to room temp, diluted to 25 ml with H O and absorbance 2 measured against a reagent blank. Beer’s law is valid from 0.4 to 16 ppm o f V. Up to 10 mg of Co, Mg, Mn(II), Cd or Pb, 5 mg of Ni(II), Co(II), Zn or Al, 2 mg of Mo(VI), 0.5 mg of Cr(III), 0.2 of W(VI) or 0.1 mg of H(rV) did not interfere. ofV(IV) were 326 fig 1 mM1 of reagent, mlof10 0.3M-NH4Cl-aq. NHfl Asample containing V(V) was with mixed of ml 10 324 buffer (pH 9.2) and HzO up to 25 ml. The soin, between V(V) and TheI. complexation reaction added 1%ascorbic acid soin. (4.5 ml), mM-I 1 (5 ml), 10%hexamine soin. (1 ml) and mM-II 1 (5 ammonium chloride in ance toluene, of andthe organic the waslaw obeyed absorb­phase for 0.5 was to40 ppm measured. and the Beer’scoeff. of Theviolet 1:10 complex at pH3 to4.2is formed 325 Toa sample containing up to22 ml). Thewasvol. made up to 25 and ml absorbance was then extd. with 10 ml of 5mM-methyltrioctyl variation was determination 0.4%. ofVin steel. The method applied to was studied with 1 mM-NH 96% VO„ ethanol. and The 1 mM-I complex in wasand extd. its intoabsorbance CHC13 was measured.obeyed from 0.12to Beer’s ppm 1.2 ofV(V). law was Microdetermination of tungsten (VI) and (V)vanadium is based on the 327 catalytic action of W 04 or therange 0.2to 0.9ppm. VOa" onVOa" the oxidation of cited reagent by Hg0pHo f 2 at 335 or 1.60 respectively.In to the 733debt, of 0.46 ofng/1 W and 0.02 to 23 mg/l of V, the was measured. The optimum pH was 4.6 to 5 3 in errorsare 13 and 2% respectively. 5-Methoxy- carbonyl pyridine- 2-hydroxamiCacid 525 om 9.2 pyridylazo)-5- e=52,900 4.2 2-(5-Chloro-2- dimethylaminophenol (I) 603 nm 3to Eriochromecyanine R(C.I. Mordant Blue3) (I) 590nm 4.6 to and Chlorpromazine hydrochloride (II) 5.3 2,4-Diaminophenol 500nm 1.60

157 KJt 0 0 Name of the Reagent X or Remarks Refs. m a x . PH working wavelength with«

N-Phenyl- 540 mn 2.7 to Samples (plant tissue, liver, blood and urine) were 328 cinnamohydraxamic acid 7.5M-HCI subjected to Kjeldahl digestion. Bach soln. so obtained was treated with aq. KMn04 at 80" to give a pink colour then made 2.7 to 7.5 M in HCI before extn. with 0.1% soln. of the reagent in o- dichloro benzene for 2 min. The absorbance of the dried extract was measured against reagent blank. Beer’s law was obeyed for 0.88 to 7.0 ppm of V. Milligram amounts of Al, Cu(II), Fe(HI), Mg and Zn were tolerated, and recoveries of added V were quantitative.

Gallic acid 380 nm 3.8 An aq. soln. of V is treated with 0.018M-gaIlic acid 329 + Bromate plus 0.96M-NaBrO3 at pH 3.8 and a double beam spectrophotometer is used for absorbance measurement. At 22* to 30", the best practical sensitivity is « 40 Pg for an absorbance change of 0.0005, which is a 50-fold improvement obtained by this method. At a level of 10 ng of V, the coeff. of variation is 10% and the limit of detection is 0.5 ng. There is no interference from Al (500 ng), Mo(VI) (500 ng), f (250 ng), Br (10 pg), Fe (5 ng) or Cu (1 pg), and s 10 pg of Ca, Mn(II), Ni(II), Zn or Pb(II) can be tolerated when determining 5 ngofV .

With 1.76 M -Br03" and 0.06 M-gallic acid at pH 330 3.8, each at 0.5 ml/min in a flow injection system, 0.2 to 20 ng of V (20 fil injection) can be determined at 30*. Oxidized gallic acid is detected at 380 nm. At 65* and with 0.5 M-BrOg", 0.05 to 4 ng of V can be determined, with coeff. of variation = 5% for 0.6 ng of V. The tolerance of Al(III), Mo(VI), I' and Cu is 10, 10, 50 and 200 ng respectively for determination of 1 ng of V at 65* and 200,200,500 and 500 ng, respectively, at 30*..

Diphenyl carbazide and 540 nm 4.5 A ternary complex (1:2:2) is formed between 331 Hexadecyl trimethyl «=50,000 to V(IV) and both reagents. Beer’s law was obeyed ammonium bromide 6 for £ 1.0 /ig/ml of V. The method was applied to minerals, rocks and coals.

N-Phenyi benzo 524 nm =Z 25M - The melt, obtained by the fusion of the sample with 332 hydraxamic acid w carbonate borate, is dissolved in 4 M-H2S04, the soln. is adjusted to — Z25 M in HgS04 and the V is oxidised to V(V) by dropwise addition of aq. 0.06% KMnC>4 at < 25*. The soln. is then extd. with 0.1% solution of reagent in CHC13 and the CHClg layer is collected and dried before absorbance measurement Results are compared with a calibration graph for up to 0.08 mg (as V ^ g ) in the final 10 ml extract Name of the Reagent X Remarks Reis. max. or PH working wavelength withe

4-(2-Pyridylazo) 592 nm 3.5 The anionic Vanadium-ciystal violet (CL Basic 333 resorcinol (I) e= 141,000 to Violet 3) complex forms a quarternary complex and H2 O 2 5.5 with HzOa and (I) ion pair complex, in buffer solution of pH 3.5 to 5.5. The complex is extd. into isobutyl methyl ketone-benzene. Absorbance of the coloured extract is measured and Beer’s law is obeyed in the range 0.05 to 0.45 /xg/ml of V. The method was used for detn. of micro amount of V in steel.

2,4-Dihydroxy- 410 nm 4.5 A sample of V-containing steel (0.3 to 1 g) was 334 benzaldehyde anthraniloyl decomposed by heating with 50% HNOg. The hydrazone (I) soln. was diluted to 100 ml with H20 and a portion (3 to 5 ml) was mixed with 5% (NH4)2S2Oa soln. (3 ml) and, after = 2 min. with acetate NH3 buffer soln. (pH 4.5, 10 ml) 5% NaF soln. (2 ml), 1% K tartrate soln. (2 ml) and a 0.05% aq. acetone soln. of the reagent. After dilution to 25 ml with H O, the absorbance was measured. The calibra- 2 tion graph was rectilinear from 0.2 to 8 fig/ml of V. the limit of detection was 0.18 ng/ml of V. Interference was caused by Mo(VI), Fe(III), W(VI), Ti(IV) and Cu(II). 4-Amino antipyrine (I) 555 nm 2.9 A sample soln. (10 to 25 ml) containing < 50 ng of 335 with NN-Dimethyl V and os 0.1 M in H Q is treated with 4 ml of 1 M aniline (II) sulphosalicylic acid, 5 ml of 80 mM-(II) in 0.1 M- H Q , 2 ml of 17 mM (I) in 0.1 M -HQ and 5 ml of 2 M-NHg. The pH is adjusted to 2.9, and the mixture is diluted to = 47 ml with HgO. After = min. at 50* ± 1, 2 ml of 0.15 M-KBrOg is added, and the mixture is made up to 50 ml, mixed vigorously, and kept at 50*; after exactly 20 min. — 5 ml of the mixture is cooled in an ice bath and its absorbance is measured. The calibration graph was rectilinear for 0 to 1.0 ng/ml of V. The coeff. of variation were 1.6 to 2.4% (n = 10). The method was applied to natural and potable waters.

5-Diethylamino- 620 nm 3.2 Asample 1 ml (containing = 10/¿gof V ) is 326 . 2-(4,5-dimethyl-2- «=41000 treated with 2 5 ml of phosphate buffer (pH 3.2) thiazolylazo) phenol and 5 ml of ethanol and is diluted to — 20 ml with HzO. After adding 1 ml of 0.25% reagent soln., the soln. is diluted to 25 ml with HgO and heated on water bath (80*) for 10 min. and the absorbance of the cooled soln. is measured against a reagent blank. The composition of the blue complex is (1:1) and Beer's law is obeyed for up to 1 jug/ml. Up to 200 fig of Fe, 50 fig of Zn and Hg, 300 fig of o Pb, 40/rgof Bi, 500fig of Mo and 100 fig of A lcan be tolerated; Cu and Co interfere seriously. The method has been used for determination of V in table salt and waste water. O s N> Refs. Name of the Reagent X m a x. or PH Remarks working wavelength withe

4-(2-Pyridylazo)- S40 nm 7.6 Asoin. containing 1 to 18 ¡ig of V was mixed with 337 resorcinol (I) e=45,600 the reagent, xylometazoline hydrochloride and phosphate buffer (pH 7.6) and V was extd. into nitrobenzene as an ion pair complex. Absorbance of organic layer was measured and Beer’s law was obeyed for up to 1.8 /tg/ml of V. The method was applied for determination of V(V) in steel and titanium based alloys.

3,4,5,6-Tetra- 385 nm 4.5 A soln. of V(V) was mixed with 2 ml of acetate 338 chlorogallein (I) e=700,000 buffer (pH 4.5), 13 ml of O.OlM-hexadecy! pyridinium chloride, 1 ml of 1% poly(N-vinyl pymJlidone) and 1.4 ml of 1 mM-I and the soln. was diluted to 10 ml with HgO, heated at 60* for 30 min. A fter cooling, the absorbance was measured against (I). The calibration graph was rectilinear up to 0.8 /ig of V(V); Sandell’s sensitivity was 60 Pg/cm2 and the coeft of variation (n=5) was 1.7% for a 0.05 fig/ml o f V(V). Aluminium (III), Cu(II), Fe(III), molybdenate, tungstate, thiosulphate, citrate and some oxidants also interfered. N-Phenyl-N-m-tolyl 530 nm A method to determine vanadium in coal and fly hydroxylamine [N-Phenyl-m- «=5250 ash has been given. Fly ash (0.2 g) was heated with toluhydroxamic add] 20 ml of HF-HN03 (1:1) at 150*, the digest was evaporated to dryness, and the residue dissolved in 20 ml of HNO3-60% HCIO^ (1:1) at 250*; the soln. was evaporated to dryness at ISO*, and the residue was dissolved in H O ( = 2 0 ml). Coal (0.5 to 1.0 g) was treated in the same way as fly ash, after ashing in a muffle-furnace. An aliquot of the final soln. was diluted to 35 ml with H_0, treated with aq. 03% KMn04 (dropwise to a persistent pink), 2 ml of said. aq. NaF, 10 ml of a 0.1% soln. of cited reagent in CHC13 and 15 ml of concn. HD, and the absorbance of the separated organic phase was measured against CHOg. Beer’s law was obeyed for 0 to 76 /ig o f V (in 10 ml of extract). Resacetophenone 410 nm 3 The cited reagent gives a yellow (1:2) complex with isonicotinqyl- «=7700 to Mo(VI) (Xmax, 440 nm) in 0.02 M-HNOg metha­ hydrazone 6 nol (1:2) and with V(V) gives a (1:1) complex in 10% DMF at pH 3 to 6 (acetate buffer). Beer’s law ranges (in ¿tg/ml) and the Sandell sensitivity (in /xg/cm2) are 03 to 8.0, and 0.01 for Mo («=9000) and 0.22 to 4.9 and 0.007 for V. For 4.8 ftg/ml of MO and 3.2 /tg/ml of V, the standard deviations are 0.005 and 0.008. In determination of V, Al, Zn, Co, Ni, Fe and Cr(VI) did not interfere. Name of the Reagent X-max. or pH Remarks working wavelength withe

N-(4-Chloro-phenyI- 570 nm For determination of V(V) in the binary complex 3,4,5-tri-methoxycinnamo- with I, the samples of rock, steel, dried plant, hydroxamic acid (I) tissues, soil or blood were digested with mixture of and NO-Bis (4-Chloro- 540 nm 2 concn. HQ-HNO^ or cone. H a-(N H 4)2S?Oa. phenyi)isobutyro- to The acidity was adjusted, and 0.1% I soln. in hydroxamicacid (II) 3 CHCI3 (10 ml) was added and the mixture was shaken for 2 to 5 min. The solvent phase was separated and extn. was repeated with more reagent (2x2 ml). The CHCIg extracts were dried (Na2S 0 4) and diluted to 25 ml with CHC13, and the absorbance of the blue-violet colour complex was measured. In the mixed ligand method, the pH of V soln. was adjusted to 2 to 3 with HC1-KCI buffer, 0.1% II soln. in isobutyl methyl ketone (10 ml) was added and the mixture was shaken for 5 min. Then NH4SCN soln. was added, the extract was separ-ated and dried (Na^Op and its absorbance was measured. Tantalum, Nb and Mo interfere but Ba, Ca, Mn and A1 do not (up to 40 mg).

Desferrioxamic ? 480 nm 1.3 This reagent forms with V(V) in HNOa soln. (pH acid «=3150 1.3) a red-violet (1:1) chelate. Beer’s law is obeyed from 0 5 to 50 ppm o t V(V) and Sandett’s sensili- 9 vity is 0.16 fig/cm of V; the coeff. of variation is 0.54%. Iron (III) and F" interfere seriously.

5-Ethylamino-2- 530 nm 3.9 A (1:2), V(V)-I complex is formed in aq. 30% pro- 343 (8-quinoIylazo)- ««42000 panoi of pH 3.9 (acetate buffer soln.) containing - -ir-xpecroA. (I) — 7 /¿M-I. The limit of detection is 40 ng/ml of V(V). Tolerable amounts of diverse ions (relative to V) are: Mg, Ca, Sr, Ba, Zr, Zn, Ag, F", SO ^, CO^ or citrate (1000); Sb, Pb, Cr(III) or Cr(VI) (500); Hg, Au, Sc, Hf, Nb, and Y (300); In, H , La, Rb, Zr, and Mn (200); Bi, Ga, As, and Sn (100); Ge, Si and H (50); Mo, Cd and Ni (30) and Co (10). The method (without extn.) is used to deL = 64 ppm of V in soils; the coeff. of variation is 14%(n=10).

N-Phenyl benzo- 530 rim 3 to Samples (200 to 250 ml of river or sea water), acid- 34 4 hydroxamic «=4950 8.2 M- ified with 2 ml of H Q and 5 ml of Fe(NO V soln. acid (I) HQ (31 mg/ml) and 20% (v/v) NHa (pH 8 to 9.6), were added to pre-concentrate V for CO-pptn. After 10 min., the resulting ppt. was centrifuged off and dissolved in 1 to 2 ml of 1 M-HgSO^; 2 to 3 drops of =* 0.05 M-KMnO^ were added (to oxidize V to V(V)). In a separating funnel, cone. HQ was added to the soln. to give a final acidity of 3 to 8.2 M and 5 ml of 5 mM-I in 1,2-dichloro benzene was added; absorbance of the separated organic layer was measured against (I). Beer’s law was obeyed and the Sandell sensitivity was 10 ng/cm2. os Name of the Reagent X or pH Remarks Refs. m ax. working wavelength withe

3,4-Dihydroxy 350 nm 5.0 The cited reagent forms coloured complex with Co 345 benzaldéhyde e * 12^00 (II), Fe(III), Fe(ll), Mo(VI), W(VI) and V(V> guanylhydrazone The optimum pH for Mo(V!) and W(VI) and [amidino hydrazone] V(V) is 5.0. The e values for Mo(VI) and W(V1) (3,4-DBGH) are 8800 at 350 nm and 15200 at 355 nm respec­ tively. Beer’s law is obeyed from 0 3 to 9 ppm of Mo(VI) and W(VI) and from 0.1 to 3.4 ppm of V(V>

2-Hydroxy-l-naph- 405 nm 43 A 0.08% soln. of I in DMF, and acetate buffer 346 thaldehyde guanyl­ ««7700 soln. (pH 45), were added to V(V) and the absor­ hydrazone [amidino bance of the 1:1 complex was measured. Beer’s hydrazone] (I) law was obeyed up to 8.7 ppm of V(V), and the optimum concn. range was 13 to 6.0 ppm. The relative error was s 0.6% for 3.5 ppm of V(V). The method applied to det V(V) in stand, steel.

2,6 Diacetyl- 340 nm 2.5 Cited reagent has been used for the detn. of 347 Pyridine bis e= 27,300 a soln. containing S30fig of Vwas adjusted to pH (benzoyl- 25 and treated with 1 mM-reagent; after 20 min., hydrazone) further HC1 was added and absorbance was measured against a reagent blank. Beer’s law was obeyed for up to 35 fig of metals. Bromopyrogallol 580 nm Vanadium was separated from turbine oil by extn. 348 red (1) and of V ( — fig in 1 to 5 g sample of oil) into 0.1% bi­ Diphenylguanidine (II) phenyl benzohydraxamic acid in CHCL. The complex obtained was mineralized at 500*, the residue dissolved in 0.1 M-NaOH and the soln. diluted to 10 ml with HgO. This soln. was mixed with 1 ml of 1 mM (I), 1 ml of 0.1 M (II) and 5 ml of acetate buffer soln. (pH 4.2), diluted to 25 ml with H£0 and shaken with 3 ml of hexane for 90 sec. Both liquid phases were discarded, the ppt. was dissolved in 5 ml of DMF; after 30 min., the absorbance of this soln. was measured. Beer’s law was obeyed for 0.1 to 0.7 fig/ml of V; the recovery of V was 93 to 103%.

2-(5-Bromo-2- 585 nm Vanadium was extd. into 0.1% N-phenyl benzo- 349 pyridylazo)-5- «=54300 hydroxamic acid in CHC13, and the extract was diethyl aminophenol washed with 4 M-HC1 and evaporated. The residue (50Bromo-PADAP) (I) was mixed with cone. HCIO. and cone. HNO . The 4 3 soln. was evaporated and the resulting residue was dissolved in HaO, then successively treated with ethanol and (I) at pH 4.5 (acetate buffer). Absorbance of the 1:1 complex was measured and Beer's law was obeyed up to 1.2 fig/ml of V. Zinc, Cd, Ni, CO, Mn, Fe(III), Cr(III), Mo(VI), Sn(IV), Cu, Pb, Hg(II) and Ag interfered. The method was applied in the determination of V in aluminium. Name of the Reagent or Xmax. PH Remarks Refs. working wavelength withe

Catechol violet (I) 550 nm 6 Complexes of V with 1,1,10-phenanthroline or 350 and Hexadecyi pyridmium with I and II were studied for determination of V bromide (It) in triglycine sulphate at' 10 ppm level. I and NSgSO^ are added to the sample soln. at pH 6, the complex is extd. with a soln. of II in CHQg and absorbance is measured. The coeff. of variation is <7% . Copper, Co and Fe interfere but Ba, Ca, Re, Sr, Al, Mg and C r do not.

Pyridine and 405 nm <7 A soln. of V(V) at pH <7 was shaken with 351 Dibenzoyl methane (II) Na2S20 4 (0.45 to 0.6 g) for >1 min. Pyridine (0.5 ml) and 0.5% soln. of II in acetone (2 ml) were added, the soln. diluted to 20 ml with H£0 and shaken for 5 min. The brown complex was extd. twice with benzene (10 ml) each). and the absorbance of the combined extract was measured. Beer’s law was obeyed up to 5 /xg/ml; the Sandeil sensitivity was 4 ng/cm .

Tannic acid 328.9 nm 5 to Determination of V(V) with tannic acid at 332.2 352 6 nm is not affected by <0.05 M-glycine-alanine or 3 amino-propionic acid; higher concn. of amino acids resulting from hydrolysis of proteins should be decomposed by Kj'eldahl digestion. A fter elimina­ tion of Fe(III) by extn. of the V-tannic add complex at pH 5 to 6 into tributyl phosphate hexane (1:1), absorbance is measured and com­ pared to a calibration graph prepared analogously with protein-free V soln.

Tannic add 332 nm Tannic add forms a 1:1 complex with V at pH 5 to ««=8500 6. Beer's law is obeyed from 0.5 to 10 ppm of V and the Sandell sensitivity is 0.028 /¿g/cm . Hydroxylamine peptones, Fe(III), Mo(VI) and WfVI) interfere^ 20-fold amounts of Na+, K+, Li . Mg2+, Ca , Fe2+, Zn2+, Cl\ F\ NO.,', S04 , PO *" and P O 4- do not. The method has been applied to detn. ofV in serum.

1- (2-Thiazolylazo)- 610 nm To a soln. (pH 2.3) containing £ 50 /tg of V(V) 2- naphthol (I) «=15,000 and 2 ml of 10% KSCN soln. were added 1 ml of 1% gelatin soln. and 3 ml of aq. 0.1% reagent. The stable red complex (1:1) produced was dissolved in 10 ml of methanol, the soln. made up to 25 ml with H20, and absorbance was measured. Beer’s law was obeyed for 0.08 to 2.24 /¿g/ml of V(V) and the Sandell sensitivity was 3 ng/cm , The coeff. of variation (n=10) was 0.82% for 50 /ig of V(V) in 25 ml. Out of 57 diverse ions only Ni(II), Sc(III), V(IV) and EDTA interfered. The method was applied in detn. of V in high speed steel. o Name of the Reagent X^w pH Remarks Refs. working wavelength with c

Semixylenol 530 nm 3.0 to A 1:1 complex is formed between V and cited re- 355 orange ««19000 63 agent at pH 3.0 to 63. Beer’s law was obeyed for up to 15 /tg of V in 25 ml of soln. The method was applied in the determination of V in waste water.

2-Thenohydraxamic 695 nm 1.9 A sola [73 to 25 fig of V(V)] is treated with 2 5 ml 356 acid ««11,000 of 0.01M-reagent, 1 ml of 0.02 M-SCN and 1 ml of chloro acetate buffer (pH 1.9), diluted to 25 ml and extd. with 5 ml o f 0.01 M-Adogen 464 in tolu­ ene. The separated organic phase is dried with Na_SO, and its absorbance is measured. Crude petroleum is digested with concn. H2S 0 4> followed by mixed acids, and steel samples with H3PC>4- HgSO^-HgO (5:1:5); the residues are dissolved in aq. 6M-HNC>3 and buffered with acetate to form the analytical soln.

N-Benzoyl-2- 505 nm 4 to The sample soln. (40 to 200fig) of V(V) in 10 to 15 357 naphthohydroxamic «=5340 5 M- ml of 4 to 5 M -HQ is extd. with 10 ml of a 0.1% acid H Q soln. of this reagent in C H Q 3. The extract is dried over anhyd. NagSC>4, diluted to 25 ml with CHQg and absorbance is measured against solvent blank. Beer's law is obeyed in the range 1.8 to 8.8 ppm of V(V) in CHQa soln. Uo(VT), Zr and Ce(IV) do not interfere, but TI(IV), W(VI) and Ti(III) interfere at 5 ml level or less. The method has been applied in the detn. of V(V) in steel.

O-Hydroxyquinol- 540 nm The test soln. was mixed with 20 mM of II (2 ml), 3S8 phthalein (I) aq. 1% L-ascorbic acid (1 ml), acetate buffer soln. with Hexadecyl of pH 5.4 (3 ml) and 1 mM- of I (1.5 ml). The mix­ trimethylammonium ture was diluted to 10 ml with H20 , heated at 45 ’ chloride (II) for 30 min., cooled and absorbance was measured. Colour remained stable for Z 90 min. The calib­ ration graph was rectilinear up to 0.8 ppm of V with coeff. of variation of 0.8% (n=5). The reagent has been used in the determination of V(V) in waste water, potable water, river and rain water, after concentrating the samples 10- to 100-fold. Coeff. of variation were < 133%.

Alizarin redS (I) 520 nm A sample of ore, alloys or slag containing = 1 mg 359 and Hexadecyl- of V was fused with Na2Og (3 g). The melt was dis­ pyridinium bromide (II) solved in hot H20 , lx>iled to remove excess of peroxides, and the soln. was made up to 250 ml with H20. An aliquot containing = 20 fig of V was neutralized with H2SC>4 )1:3), mixed with aq. 0.5% NaF (0.5 ml), 0.01 M of I (0.6 ml), 0.01 M-II (6 ml), 5% ascorbic acid (1 ml) and glycine buffer soln. of pH 33 (5 ml); diluted to 25 ml with HgO and after 10 min. absorbance was measured against a reagent blank. Beer’s law was obeyed from 0.4 to 2.4/tg/mlofV. Name of the Reagent X or Remarks Refs. m ax. working wavelength withe

Diphenyl 544 nm A steel sample was dissolved in hot H2S 0 4* 360 carbazide *=76,000 H3P 04-Hg0 (1:2:3) and was further treated with HN03 and with a masking agent comprising 1% NaF soln. and 2% tartaric add soln. At pH 5 (sodium acetate-acetic add buffer) 0.1% KMn04 was added. After 3 min., 0.2% of the reagent containing 15% of O.P. emulsifier was added and absorbance was measured. Beer’s law was obeyed up to 0;6 fzg/ml o f V., Tartaric add and citric acid did not interfere.

3-(2-Fuiyl)-N- 450 nm The method involves selective ectn. of V from 3 to 361 (4-methoxyphenyl)- *«14000 8M-HC1 medium with a CHC13 soln. of (I). The acrylohydraxamic acid (I) red-violet extract (<=8600 at X _ = 545 nm) is and 2-(3-(Phenyitriazene- then equilibrated with (II) at pH 1.5 resulting in 1-benzoic acid) the formation of ternary complex. Beer’s law is N-aride (II) obeyed up to 18 ftg/inl of V. The method permits detn. of V at ppb levels. Many cations and anions normally present with V in rocks, plants, animal tissue and water do not interfere. Betyilon {4-[4-{dielhyJ- 475 nm The catalytic action of V(V) on the reaction 362 amino)-2-hydroxy-phenylazo]- between I and II has been shown to have a 5-hydraxy-naphthalene- rectilinear relation to the concn. of V and has been 2,7-disulpbonicadd} (I) used for determination of its trace amounts in and Ascorbic add. (II) rocks and minerals. Absorbance was measured as the difference between readings, with and without the addition of ascorbic add.

2-(5-ChIoro-2-0 586 nm The sample was dissolved by heating successively 363 pyridylazo)-5- with H S O -H N O . and HCL The dil. soln. was fil- dimethylamino tered and the filtrate was mixed with H O, phenol (I) H3P 04, a little KMn04 soln. and 6M-NaOH to pH 9. The soln. was mixed with aq. NH3*NH4C1, buffer soln. (pH 9.5) and other metals were removed by extn. with quinolin-8-ol in Chcl3< The aq. phase was mixed with acetic add • Na acetate buffer (pH 3.8) and ethanolic 0.2% reagent and absorbance was measured. Beer’s law was obeyed for 0.1 to 1.2 ppm of V(V).

The binary mixtures Ti-VtTi-Mo and V-Mo were 364 analysed. At an isosbestic point for the peroxo- complex of one constituent, the derivative absorbance of the other constituent was red and used for quantitation. Calibration graphs were constructed. Suitable operating range (pg/ml) for V were; 0.7 to 400 at 326.4 (in presence of Mo) and 6 to 400 at 407.6 nm (in presence of Ti). •»* Name of the Reagent \rwuc.0r pH Remarks Refs working wavelength withe

Diphenyl 530 nm 1 N- Sample soln. containing £ 40 ¿tg of V was mixed carbazide e=41,000 H,SO_ with 1 ml of reagent, pyridine (2 ml) lN-HgSO^ 2 4 (0.4 ml) and HgO to - 10 ml. After 30 min., the violet complex was extd. twice, with 10 and 5 ml of CHC13, having been shaken for 30 sec. each time. To the combined extracts were added anhyd. Na SO , the vol. was made up to 25 ml and absorbance was measured. Beer’s law was obeyed up to 1.6 pg/ml. Oxalate, tartrate, citrate, EDTA, and ascorbic acid interfere. The method was applied to detn. of V in synthetic samples.

Pyrazinohydroxamic 430 nm 2.8 In aq. medium (pH 7.2 to 8), V(V) forms 1:3 and acid (I) 1:1 complex as with (I). These can be extd. at pH Adogen 464 (II) 515 nm 7.2 2.8 (H O , KH-phthalate) in hexanol, at pH 7.2 to 8 and to 8 (phosphate buffer) into 10/xm-II in ethyl acetate 520 nm 7 to 8 or at pH 7 to 8 (phosphate buffer) into 1 mM-II in toluene; absorption max. are at 430 nm, 515 nm and 520 nm, respectively. Beer’s law is obeyed for 0.5 to 8 ppm of V with Il-ethylacetate methanol. Cobalt (1 ppm) interferes. The method has been applied in the detn. of V in crude or fuel oil after wet ashing. Ferron [8-hydraxy- 390 nm 0.08 The sample soln. containing <200/ig of V(V) was 367 7-iodoquinoline-5- to mixed with 10 to 15 ml of 0.1% soln. of the reagent, sulphonic acid] (I) 0.12N- 1 ml of 0.08 to 0.12N-H SO and H O to 20 ml. 2 4 2 H2S 0 4 The complex was extd. with 10 ml of 1 to 2% tribenzyl soln. in CHC13 for 1 min.; the aq. phase was re-extd. with 10 ml of solvent, the extracts were combined and the soln. was diluted with CHC1 to 3 25 ml. The absorbance was measured vs. a reagent blank. Beer’s law was obeyed up to 10 /ig/ml of V(V), the Sandell sensitivity was 6 ng/cm . The method was used in the determination of V in natural and industrial materials.

2-(5-Broroo-2-pyridylazo)- 603 nm 1 In acidic medium at pH 1 to 2, V reacts with both 368 5-diethylamino phenol «=61100 to the reagents to form a ternary complex. Adsorp­ (5-Br-PADAP) (!) 2 tion max. of the complex was determined; Beer’s and Hydrogen peroxide (II) law was obeyed for 0 to 20 jug V.25 ml. By using a masking agent, common ions did not interfere except Co(II) and Co(III). V was determined in various alloys.

2-Salicyliden- 490 nm 2 J To the test soln. were added 10 ml of ethanolic - 369 aminobenzohydraxamic «=4700 5.25 mM - reagent, 2 ml of chloroacetate buffer acid (I) 380 nm soln. of pH 2.5 and H2C>2 to 25 ml and absorbance «=3400 was measured against reagent blank at 490 nm [for 4.0 to 9.0 ppm of V(V)J or 389 nm for (IB to 8.0 -a U l ppm). o Name of the Reagent \nax.or pH Remarks Refs. working wavelength withe

Hexadecyltrimethyl 416 nm 5.2 The colour reaction of Al, Ti, V, Mo and W with 370 ammonium bromide «=19,800 to cited reagent was observed at X of 425,428, (CTMAB) 5.8 416, 425 and 416 nm with «=28,200, 56,300, 19,800, 40,300, 50,100, respectively. The corresponding pH ranges were 5.6 to 6,4.8 to 5.8, 5.2 to 5.8,4.6 to SS and 4.4 to 5.1. Mo and W in steel and TI in germinated speed samples were detd. satisfactorily.

Thioproperazine bis- S13 nm 10M- To a soln. containing V(V) 15 to 150/«g were 371 (methanesulphonate) «=8950 HPO, added 15 ml of 10M-HPC) and 3 ml of an aq. 1% 3 4 reagent soln. The mixture was diluted to 25 ml with HgO and the absorbance was measured. Beer’s law was obeyed from 0.1 to 6.8 ppm of V(V). In the detn. of 2 ppm of V(V), the relative error was <2% (n=6). The method was applied in the analysis of steel and minerals. Interference by 30 metals and ions is discussed.

Isophthalohydroxamic 610 nm 2.7 Three methods for determination of V(V) have 372 acid (I) 675 nm & been developed, based on extn. of a mixed complex 405 nm 2.7 in presence of a 2.5 M-chloroacelic add - Na 620 nm 2 chloroacetate buffer with a soln. of Adogen 464 in toluene and measuring the absorbance of the orga­ nic phase. The complexes used, pH and wave lengths for measurements ate: V(V)-SCN"-I (1:1:2), pH 2.7, 615 nm (method i), V(V)-SCN I (1:4:1), pH 2.7, 675 nm and 405 nm (method ii) and V(V)-Oxalate-I (1:1:1), pH 2,620 nm (method iii).

3,3-Diantipyrinyl- 550 nm H 3 P ° 4 A soln. containing 5 jug of V(V) is mixed with 1 ml 1-phenyl-prop-l-ene £=20,000 of 0.1% Mn (as MnSO ), 4.5 ml of concn. H PO , 3 ml of ethanolic 0.1% reagent and 0.5 ml of 1% polysorbate 40 and then diluted with HgO to 25. After 20 min., the absorbance is measured vs. a reagent blank. Beer’s law is obeyed for up to 7 jug of V in 25 ml of soln. The method has been applied for direct detn. of V in ores, but pre-separation is needed for detn. of V in steels.

Chromotropic acid (I) 430 nm 3.8 The sample soln. (1 ml) is mixed with 1 ml of 1M- acetate buffer soln. of pH 3.8 and 2 ml of a 1% soln. of di-sodium salt of I and the mixture is warmed with 5 ml of 5% KBrO soln. to 30*. After 3 10m min. the reaction is stopped by the addition of solid Na-oxalate, while stirring. After 10 min. the absorbance is measured at room temp. The calib­ ration graph covers the range from 5 to 80 ng/ml of V(V). Copper and Fe(III) interfere, but 10,000- fold amounts of Zn, Mg do not. The coeff. of variation (n= 10) at 16 ng/ml of V was 4.4%. -a oo Name of the Reagent X or Remarks Refe. m ax. PH working wavelength withe

l,8-Diamino-4,5- 602 nm 4M- A 6.5 ml portion of 0.4 mM-reagent was mixed 375 dihydroxy anthraquinone- HQ with 4 ml of 4M-HQ, the sample soln. and HzO to 2,7-disulphonic acid . 25 ml. After 15 sec. the absorbance vs. time graph was record at 25* vs. a reagent blank. The calibration graph was rectilinear between 2.5 and 4.5 and 73 and 50 ftg/ml of V; coeff. of variation were 0.3 to 4.4%. The method was applied in the detn. of V in crude oil.

5,5'-Ditliiodt- 550 nm 5 A soln. containing 12.5 to 50 ng of V(V) is added 376 (salicylohydroxamic- to 15 ml of 0.02 M-reagent plus 8 ml of 0.2 M- acid) (DTD-SHA) acetate buffer of pH 5.0; the complex is extd. from the mixture (diluted to 25 ml) into 10 ml o f 5 mM- Adogen 464 (methyl trioctylammonium chloride) in toluene and absorbance is measured against Adogen 464 soln. Beer’s law is obeyed for 0.4 to Z0 ppm of V in the aq. phase. For detn. of V in steel, the steel is dissolved in H20 -H 3P 0 4-conc. H2S 04 (5:5:1) with heating as necessary (if a black ppt. forms, HNOa is added dropwise, while boiling, until it is dissolved). This soln.. is neutralized with aq. NHa, buffered with acetate and filtered before detn. of V by the above procedure. Methaxypromazine 625 nm 10M- The sample soln. of ilmenite was treated with 0.01 377 maléate M-KMn04 [to oxidize any V(IV) to V(V)] until H 3P 0 4 the soln. was pale pink;-5 mM-oxalic ad d was added until pink colour disappeared. After dilution with HzO, a portion containing 2.5 to 1623 /ig of V was mixed with 10 M-H3P04 (5 ml) and aq. 0.1% reagent (2 ml), and diluted to 25 ml. The absorbance was measured and Beer’s law was obeyed from 0.1 to 6.5 mg/1; relative errors (n*10) were from 41.66 to 4-1.6% in the range of 1 to 5 mg/1 and recoveries were from 99.3 to 101.6%. Iron(II), Cr(VT) and Ce(IV) interfered at all concn. studied.

Phenyl ethylene- 540 nm H3P04 A sample containing 0.004 to 0.18% of V is dis- 378 diantipyrinyl- e=425,000 solved in a mixture of 4 g of NaOH and 10ml of methane [3,3-dianti- HgO by heating, then mixed with 30 ml of 60% pyrinyl-l-phenyl propane] H3P04 and diluted to 100 m l A portion (5 ml) is treated, in order, with 0.03% KMn04 soln. to a reddish colour, 03 g of urea, 03% NaNOg soln. to colourless and 7 ml of 60% H PO .. The soln. is then mixed with 8 ml of MnS04 soln. containing 1 mg/ml of Mn and 2 ml of a 05% soln. of cited reagent in aq. 50% ethanol, and diluted to 25 ml; after 30 min. the absorbance is measured vs. a reagent blank. Beer's law is obeyed fcr 0.04 to 0.2 fig ml of V. Name of the Reagent k or Remarks Refs. m ax. working wavelength withe

N-(4-Aminophenyl)- 450 nm A sample soln. (25 ml) containing 0.2 to 15 ppm of 379 2-thenyl-actylo- V was extracted with 0.1 M-(I) in CHC13 (2x5 ml). hydroxamic acid (I) The combined extract was dried over Na SO. and £ 4 and 3-(2-Carboxyphenyl)- mixed with 50 mi of HgO; the pH was adjusted to 1-phenyl triazene 1.5 ± 0.05 with = 5M-HN03 and lM-NaOH, and N-oxide (II) 15 ml of 50 mM (II) in acetone was added. After shaking for 15 min, the CHC13 layer was diluted to 25 ml and absorbance was measured. Beer’s law was obeyed. The method has been used to determine V in alloys, rocks, water, plants and animal tissues.

Chromazol KS [trisodium- 600 nm Vanadium (4 fig) is mixed with acetate buffer soln. 380 3-(l,8-(dihydroxy-3,6-di- e=380,000 2 ml; pH 5.0), aq. 1% ascorbic acid (2 ml), aq. sulpho-2-naphthyIazo)- 0.1% (I) (4.5 ml), ethanol (5.5 ml) and ethanolic 2-hydroxy-5-sulphobenzoate] (I) 0JS% (II) (3 ml). The mixture is diluted to 25 ml and Hexadecyi pyridinium withH O and absorbance is measured vs. a re- 2 bromide (II) agent blank. Beer’s law is obeyed for up to 4 fig of V(IV) in 25 ml of soln. Gallium and Be interfere seriously.

Chromotropic acid 420 nm Fine steel drillings were dissolved in HC104- 381 H3P 04-HaO (11:3:1) and the soln. was heated to fumes until it refluxed. After cooling and filtration, the filtrate was diluted with H20 to 100 ml, aliquots were mixed with cited reagent at pH 13 and absorbance of the solution was measured. Beer’s law was obeyed for up to 12 ppm of V and results were reproducible.

Haematoxylin 4SS nm A simple and sensitive method for determination 382 of trace V(V) in water has been described. At pH 4.6 (acetate buffer), V(V) catalyses the oxidation of cited reagent and strongly coloured oxide is formed. Absorbance of the oxide is measured and sensitivity is improved sevenfold in the presence of cationic surfactants, e.g., hexadecyltrimethyl ammonium bromide.

3,5-Dinitrocatechol (I) 630 nm To the sample containing S 3 fig of V, at pH 5 to 383 and Brilliant Green (II) «=17000 7, were added 1 ml of 0.8 mM-(I) (in aq. 20% ethanol), 1 ml of 0.25 M.H2S04, H O to 10 ml, 5 ml of CCl^ and 0.5 ml of 0.8 mM-II (C l. basic Green). After shaking for 1 min. and settling, the CG4 phase was separated and after the addition of 1 ml of ethanol and one drop of 0.01M-H2S 04, was diluted with CC14 to 10 ml and its absorbance was measured vs. a reagent blank. Titanium, Mo, W, EDTA and SCN* interfered seriously. Recoveries were 94.0% (n=7) with coeff. of variation of 6.1%. The method has been applied to determine V at — 0.1 ppm in alums. Name of the Reagent Xm a x. or pH Remarks Refs. working wavelength withe

3,5-Dionitrocatechol (I) 555 nm 0.1M- A sample soln. containing < 3 ¿ig of V was mixed 384 and Rhodamine B. (II) £=210000 H2so4 with 1.5 ml of aq. 25% ethanolic 0.5 mM-I and 1 ml of 0.5 mM-II and diluted to 25 ml with HgO. The pH was adjusted to 2.2±0.2 with H2SC>4 or NaOH, a 5 ml portion of cyclohexane was added and the soln. was shaken for 1 min. After separation of the phases both were removed to leave the ppt. which was then washed with 5 ml of hexane and 2 ml of HgO for 30 sec. The liquid phases were discarded and the ppt. was dissolved in acetone. The soln. was acidified with 0.1 ml of 0.1M -HSO and 2 4 diluted to 10 ml with acetone. Absorbance was measured vs. a reagent blank. Beer’s law was obeyed for 0.003 to 0.3 /xg/ml of V and detection limit was 3 ng/ml. EDTA,a Ti, Zr, Mo and W interfered seriously. The method was applied to determine V in spinach, kale and parsley. Recoveries were 94 to 96%.

2,6-Dihydroxy-3 550 nm 4.25 To the sample soln. containing 5 to 40 fig of V(V) 385 (2-thiazolylazo)- are added 10 ml of ethanolic 0.5 mM-reagent, 2.5 benzoic acid ml of 1 M-NaC104 and 3 ml of acetic acid-Na acetate buffer of pH 4.25. The mixture is diluted to 25 ml with HzO, and after 20 min, the absorbance is measured vs. a reagent blank. Zinc, Pd(II), Be(III), Fe, Cu(II), Cd, Co, Ni and EDTA interfere. The method has been applied for determination of V in steel.

Enoch rame 5320 nm 1M- The test soln. containing up to 0.8 ng of V(V) is 386 Blue Black R Acetic diluted with H O to = 10 ml and then successive- 2 acid ly treated with 5 ml of 1 M-acetic acid, 2.5 ml of 1 mM-reagent in aq. 50% ethanol, 5 ml of 0.01 M- KBrO and H O to 25 ml. The mixture is kept in a boiling water bath for 18 min., cooled and absorbance vs. HzO is measured and compared to a V-free blank. The calibration graph is rectilinear for S 32 Pg/ml of V. The method has been applied in the determination of V in water.

Molybdovanado 640 nm 1N- To the sample soln. containing V were added an 387 phosphoric acid h 8s o 4 excess of aq. 2% reagent and aq. 0.02% KH2PC>4, and the soln. was made 0.4 to 0.8N in HSC>4, diluted to = 15 ml and extracted with butyl acetate (3x15 ml). The aq. phase was adjusted to = IN with dil. H2S04, 1 ml of reducing agent (aq. 1% ascorbic acid or SnCy was added; after heating at 100* for 10 min. or after 3 min. at room temp, (for soln. containing ascorbic acid or SnCl2 respectively), the absorbance of the blue soln. was measured. The calibration graph covered the range from 1 to 12 /ig/ml of vanadate. Name of the Reagent X or pH Remarks Refs. working wavelength withe

1- Methoxy-N-phenyl- 540 nm 2.25 to A method for determination of V in titanifeFous 388 2- naphtho-hydroxamic 4.5 M- iron ores with the reagent is described. Vanadium add (PMNHA) HC1 is extracted into CHC1 soln. o f the reagent from (2.25 to 4.5 M) HQ. The absorption of the 1:2 violet complex is measured. Beer’s law is obeyed for up to 28 ppm of V.

N -(4-ChIorphenyI)- 590 nm 1 J The sample soln. was diluted to 25 ml with H O 389 N-hydroxy-N'-(2^- to and adjusted to pH 1.5 to 5.2 with 2 M-HQ. After xylylj-p-tolttamidine- 5.2 addition of 15 ml of 3 mM reagent and 5 ml of 0.2 hydrochloride M 4-hydroxybenzaldehyde (both in CHQa), the mixture was extracted by shaking for 2 min, dried (Na2S04) and diluted to 25 ml with CHQg, and the absorbance was measured vs. CHQ3. Beer’s law was obeyed for 0.8 to 6.4 ppm of V. The coeff. of variation (n=10) for 4 ppm was 0.8%. The method has been applied in analysis of steel. o-Dianlsidine 440 nm h 2S° 4 A standard soln. containing 10 to 100 /ig of V(V) 390 was mixed with 10 ml of 0.1% Fe(II) soln. and 15 ml of H Q 0 4-H3P 0 4-H20 (11:3:1), and the mix­ ture was evaporated on a hot plate to = 5 ml. The cooled soln. was diluted to 25 ml, mixed with 4 ml of 0.05% reagent soin, in dil. H SO and set aside for 5 min. After dilution to 100 ml, the absorbance was measured within 30 min. Beer’s law was obeyed for 0.05 to 2 /¿g/ml of V(V). The method was applied for determination of V in steel.

2-Benzylidene- 490 nm 3.0 The cited reagent (HL) is proposed for the 391 amino benzohydraxamic and determination of V(V) at pH 3.0. It is possible to acid 380 nm determine V(V) between 60 and 272JS /tg at 490 nm and between 52.5 and 260 /ig at 380 nm. By extn. with isoamyl alcohols, between 20 and 80 pg of V can be detd. The method was applied to fuel oil and basic slag. The composition of the complex is 1:2, V:HL. Also solid V 0L 3-2H20 was prepared and studied.

9-(2-Chlorophenyl) 560 nm 4 The cited reagent and surfactant were used at 392 fluorone and «=51000 respective concn. of 0.05% and 0.1% in acetic Hexadecyl trimethyl buffer at pH 4.0 to form a complex with V(IV). ammonium bromide Beer's law was obeyed for up to 1.2 /tg/ml of V in the final soin. o-Chlorphenyi 558 nm 6.2 The highly sensitive chromogenic reaction of V 393 fluorone (I) «=110000 to and the cited reagents (I and II) result in the form­ and Cetyltrimelhyl- 6.6 ation of a ternary complex, at pH 6.2 to 6.6. Iron bromide (II) was masked by extraction with MIBK. Beer’s law was obeyed in the range of 0 to 6.0 /¿g of V/25 ml. The method has been applied to determine micro amounts of V in steels. Name of the Reagent X or pH Remarks Refs. working wavelength withe

Sodium perchlorate 400 to 8.1 A method for determination of V and Co in steel is 394 650 nrn described. The sample (0.1 to 1.0 g) was dissolved in 6M-HC1-HNC>3 (1:1), evaporated to near­ dryness and the residue was dissolved in 6M-HCI (final vol. 100 ml). The soln. was extracted with isopropyl ether to remove Fe. The sample soln., containing 2.6 to 26 fig of V and 3 to 30 fig of Co, was mixed with 2.5 M-NaClC>4 tris HCiO buffer soln. (pH 8.1) and methanol and diluted with H^O to 25 ml. After 15 min. the second derivative spectra were recorded against a reagent blank. The calibration graph was rectilinear.

4-Aminoantipyrine (I) 555 nm 0.15 M- A 0.2 ml sample was injected into a carrier steam 395 and NN-Dimethylaniline (II) formate (0.8 ml/min), which was then mixed with steams (0.8 ml/min) of (i) 4 mM I, 30 mm II and 0.1 M Tlron; (ii) 0.08 M BrOg and (iii) 0.15 M formate buffer in a coil (10 ml x 05 mm) at 55". The absorbance was measured. The calibration graph was rectilinear for 0.05 to 2 ng/ml of V(V); the detection limit was 20 pg/ml. Coeff. of variation for 1 and 2 ng/ml were 0.8 and 0.5% (n-=10) respec­ tively. N-Benzoyl-N-phenyl 600 nm 0.1M- A sample soln. containing £ 7.6 fig of V(V) was 396 hydroxylamine (I) and «=54000 Acetic mixed with 03% KMnO^ soln. until a pink colour 2-(5-Bromo-2-pyridylazo)- acid appeared, followed by 20% urea soln. (03 ml) and 5-diethylamine phenol (II) 03% NaNOz soln. until the colour disappeared. After the addition of satd. NaF soln. (2 ml) and HQ to 4 M, and dilution to vol., V was extracted into CHQ3 (10 ml) containing 0.02% of (I). A 5 ml portion of the organic phase was shaken for 30 min. with 4 ml of 0.1% (II) soln. in DMF, 1 ml of 4% KJO, and 10 ml of 0.1 M-acetic acid. The absorbance of the organic phase was measured vs. a reagent blank. Beer’s law was obeyed for up to 3.8 fig of V. The method was applied in the analysis of exhaust gases, airborne particulates and sediments.

N-4-Octylaxybenzqyl- 570 nm 5M- Sample soln. was mixed with 20 ml of 5 M-H2S 0 4 397 N-phenyl hydroxylamine «=7900 to find acid concn. of 2 M. Then, 2 ml of 1% H 2 S 0 4 ammonium per sulphate soln. was added, and diluted to =s 45 ml with H20 , then 10 ml of 0.1% of reagent in C H Q 3 and 5 ml of 0.01 M-NH^SCN were added. After shaking for 6 min, the organic layer was dried with Na2S04 and absorbance was measured vs. C H Q . Beer’s law was obeyed up to 4.6 fig/ml of V(V). The coeff. of variation (n=10) was 0.8% for 273 fig of V(V). Tungstate and Cr(VI) interfere. oo Name of the Reagent X or pH Remarks Refs. working wavelength with e

2-Hydroxy 350 nm 4 or A sample soln. (15 ml) containing 10 to 50 fig of 398 acetophenone oxime and 400 nm 2 3 V(IV) or 10 to 100 fig of V(V) is treated with 1 or 1.5 ml of 13% soln. of the reagent in aq. 50% methanol and with 7 ml of acetate buffer soln. (pH 4.0) or acetate-HCl buffer soln. (pH 23) respectively, and the mixture is extracted with 10 ml of CHC13 by shaking for 3 min. The organic phase is dried with Na2S04 and absorbance is measured at 350 nm vs. a reagent blank. When the two species are present together, the mixture is treated as for V(IV) and absorbance is measured at both 350 and 400 nm. Errors were between < 2% to 4.0%. 2,6-Dihydroxy 580 nm HBrO. Kinetic spectrophotometric determination of Iron 399 isonicotinic acid (III), Copper (II) and V(V) in the presence of each other is described. A sample soln. containing up to 100 ng of V(V) is treated with 1 ml of 10 M acetic acid and 1 ml of aq. 0.01 M-reagent. A further 1 ml of 0.1 M-HgO is added to the soln. and the soln. is diluted to 10 ml with H O. After 40 min. the absorbance is measured. The method has been applied in the analysis of lake water. Hydrogen peroxide 450 nm H2so4 A sample (1 gm) containing < 140 mg was digested 400 with 10 ml of HNOa and 2 ml of HF in a Pt dish and 40 ml of saturated H3BOg were added. The soln. was diluted to 100 ml with H O . A 10 mi 2 aliquot of this soln. was mixed with 10 ml of H2SC>4 and 10 ml of water, and was cooled in running water. One ml excess KM n04 soln. (03 wtVvol.%) was added. After 5 min. 0.7 ml of NaNOg soln. (3 wt/vol.%) was added while vigorously stirring in the presence of 4 ml of urea soln. (50 wtyvol.%). Absorbance was immediately measured after adding 3 ml of H20 2 (3%) and diluting to 50 ml with HO. The method has been used in 2 determination of V in Zr-Ni and V alloys.

Phenyl ethylene di- 540 nm H3P04 Vanadium was determined by reaction of cited re- 401 antipyiyi methane 7 «*=425000 agent and V in the presence of Mn in H3P04 medium. The complex was stable for 30 min. to — 12 hr. Beer’s law was obeyed in the V concn. range o f 1 to 5 fig/25 mL The method was applied to d eterm in e V in A1 and A1 alloys.

Di-2-Pyridyl ketone- 545 nm Acidic The reagent was tested with 36 cations in slightly 402 2-pyridyl hydrazone (DPPH) ««14000 , acidic medium, in the presence of NHaO and EDTA, but only V(II) formed a stable red com­ plex. Therefore, this method was used for determi­ nation of V(II) in the presence rtf remaining cations. vO A. o r PH Remarks Refs. o Name of the Reagent max. w orking w avelength w ith *

Perphenazine bromate 525 tun 1.5M A kinetic study on the catalytic effect of V(V) on 403 reagent soln. was carried out. The reaction was followed by measuring the absorbance under optimum conditions (1.5 M -HJ’OU 0.0005 M- KBr03, 0.15 fig ml V(V), at 25*C). The reagent is determined between 1x10"® to UxlO"4 M and V(V) between 0.01 to 0.4 /ig/ml. The procedure was applied to the determination of perphenazine in pharmaceutical preparations and to the d eterm in atio n o f V in ste e ls.

L-a-Methyl-3,4- 560 nm Vanadium (V) was determined by reaction with 404 dihydroxy phenyl­ €=2000 cited reagent Beer’s law was obeyed up to 500 alanine (M-dopa) ppm of V. The method was applied for determin­ ing V in sedimentary rocks.

o-Nitrophenyl 540 nm 2.5 Vanadium forms a ternary complex with cited re­ 405 fluorone (o-NPF) and e= 4 7 7 0 0 to ag en ts in pH 25 medium. Beer’s law is obeyed in Cetyl pyridinium 5 the range 0 to 20 fig/25 ml. Composition of the ch lo rid e (C P C ) complex is V :0-N PF: CPC = 1:3:3. The relative standard deviation was 0.14 to 3.1% and recoveiy of V was 995 to 101.4%. The method has been applied to determine V in quartz. 2-(5-Bromo-2- 595 nm 1.2 Vanadium is determined by a complex formed at 406 pyridylazo)-5- e» 6 6 0 0 0 pH 1.2 between V and reagent in the presence of (diethylamino) phenol OP surfactant. The complex is stable for 1 hr. and the colour intensity reaches max. 3 min. after the reaction of V and reagent. Beef’s law is obeyed in the V concn. range of 0 to 18 fig/25 m l. T h e method has been applied in determination of V in alloy steel.

3,5-Dichloro-salicyl- 460 nm 3.0 A ternary complex was formed between V(V) and 407 aldehyde-2-benzothiazolyl- to cited reagents as I:V5+:IL I was prepared by re­ hydrazone (I) and 4.8 fluxing equimolar amounts of 2-hydrazinobenzo- Tetradecyl dimethyl benzyl thiazole and 3,5-dichloro salicylaldehyde in 100 ml ammonium chloride (11) ethanol for 30 min. 5 ml of buffer soln. (pH 3.5,0.2 M acetic acid + 0.2 M-Na acetate) and a 2 ml 0.05 M-1I soln. were added to a sample soln. containing S 60 fig V, diluted to 10 ml with HgO , mixed with a 10 ml S.QxlO'Vl (I) soln. (chloroform), and shaken vigorously for 5 min. The absorbance of the organ­ ic phase was measured. Beer’s law was obeyed up to 60 fig V in 10 ml CHC13. The coeff. of variation fo r 20 fig V was 0.71. Li+, Na+, Mgz+, K+. Cu2+, 1000 fig each; Ba2+, Al3+, Ag+, Cd2+, Pd , 200 VO each; Au3+, 100 fir, Mn2 , Cr2+, 20 ¡1% each; Bi2+, Ca2+, Fe3+, Ni , 10 fig each; N 03', SO ^, 5000 mg each; and Cl 1000 mg, do not interfere within ± 3% for the determination of 20 fig V5 + . VO K í Name of the Reagent X o r Remarks Refs. max. w orking w avelength w ith e

5-Bromo salicyl- 552 nm Vanadium forms a ternary complex with I and II. 408 fluorone (I) and «=127000 The composition of the complex is 1:2:2 (V:1:II). Cetyltrimetihyl- Beer's law is obeyed for 0 to 8.0 fig V I25 m l. T he ammonium bromide (II) interference of iron can be eliminated by • extraction with MIBK. The method has been applied to determine micro amounts of V in steels.

Thiocyanate (I) and. 530 nm The colour reaction of V(V) with I and II (dyes 409 Basic triaiyi «=255000 such as crystal violet (CV), Malachite green, m ethane dyes (II) Brilliant green, Methyl violet and Victoria blue 4 R) in the presence of some surface active agents in aq. soln. was studied. The system of V(V)-I-CV (Arabic gum) was studied in detail. The composition was V(V): SCN*:CV = 1:4:3. The method has been applied to determine micro am ounts o f V in A ! alloys.

4-(2-Pyridylazo) ' 580 nm The anionic complex of VOz (PAR) reacts with • 410 resorcinol (PAR) «=2780000 ethyl violet in the presence of (PVA) to form an + ethyl violet ion association complex. Beer’s law is obeyed in + polyvinyl alcohol (PVA) the concn. range 0 to 3.0 pg/25 ml of V. The method was applied to the determination of trace amounts of V in cast iron. 4-Su!pho-2-amino 490 nm 0.16 to A new selective method for determination of 411 benzene thiol «=4500 0 3 6 V(V) in acetone medium in presence of Fe(UI) M-HC1 and Ti(lV) is reported. A rose-red (1:1) complex is formed between V(V) and cited reagent in the acidic range of 0.16 to 0.36 M-HCL The system obeys Beer’s law over the range 1 to 16 ppm. The method is free from unusual interference. V in alloy steel has been determined with ± 0.003% as th e average e rro r.

3,5-Diamino benzoic 480 nm The method is based on the V(V)-catalyzed oxid­ 412 acid dihydrochloride (DABA) ation of the reagent by potassium bromate. The reaction is followed by measuring the rate of change in absorbance with time. V(V) was determined in the range 3.06 to 50.94 ng/mL The method was applied to determination of V in tap water and steel samples.

N-Phenyl benzo ■ 560 nm 5 M - Vanadium (V) is extracted with (PBHA) into 413 HC1 CHC1 from 5 M-HC1 medium and determined hydnscamic acid «=36000 a (PBHA) and from colour development by addition of (PAR) in 4-(2-Pyridyiazo) DMF. Absorption of the mixed ligand complex is resorcinol (PAR) measured and obeys Beer’s law up to 2.0 pg/ml of V. The composition of the V(V) : PBHA : PAR complex is 1:1:1. The method can be directly applied for the determination of V in steels. In the case of H base alloys, separation from the Ti matrix gives good results even at 50 to 200/tg of V fo rg le v e l. ( Name of the Reagent X or pH Remarks R e f s . w orking wavelength w ith e

4-(2-Pyridylazo) 584 nm 4 In HOAC-NaOAC buffer soln. at pH 4 to 6 con­ 414 resorcinol (PAR) e»4000 to taining (CYMAB) V(V) reacts with Ha0 4 and and Hydrogen peroxide PAR to form a multicomponent complex. Beer’s and Cetyl trimethyl law is obeyed for 0 to 2.5 jig V/10 ml. V was deter­ ammonium bromide (CYMAB) mined in water samples with this method.

Alizarin Dye S (I) 520 nm A cidic T h e stab ility o f V(IV) chromophore-cationic sur­ 415 Alizarin Complexone (II) 560 nm factant complexes on a structure of organic re­ Carminic acid (III) and agents of the hydroxy- and amino anthraquinone Alizarin (IV) 570 nm series were studied. As chromophores, aq. solns. of Qumalizarin (V) (I), (II), (III), (IV) an d (V) were used. The cationic N-Cetyl pyridinium surfactants were O.OlM-soln. of (VI) and 0.01 and bromide (VI) 0.05 M (VII). The soln. to be studied contained N -C etyl pyridinium V SO and H_SO . In the acidic region, chloride (VII) complexes of V-I-VI (o r VII), V-IV-VI ( o r VII), an d V-n-VI (o r VII) w ith X ^ 520 nm ; V-IH-VI ( o r VII) with X » 570 nm; and V-V-VI (o r VII) with X ma^60 nm, were formed. The composition of all these complexes was found to be 1:2:2. The tendency towards increasing stability of th e V(IV) complexes with organic reagents and cetyl pyridinium is in the order: V < III, VI < I, II. The best systems for anal, applications are: V-I-VI (or V II). V-n-VI (or VII) and V-Vi (or VII). Mandelohydraxamic 500 nm The cited reagent reacts with Fe(III) to give an 416 acid «=5410 orange yellow BuOH extractable complex (1 = 430 nm, e = 1.15 x 104 1/mol.cm) and forms a violet trioctyl methylammonium chloride (Adogen 464)- toluene-extractable complex with V(V). The conditions for extraction were studied. The method was applied to the simultaneous determination of V(V) and Fe(III) in plant tissues such as barley, com, wheat, cauliflower and potato.

Pyrogallol [Ar(OH)3] (I) 430 nm A sensitive and selective method for sepn. and 417 and Hydroxy amidines to 440 nm extraction-determination of V(V) at ppb level with (HOA) «=520000 I and (HOA) is described. The molar absorptivity to 1500000 of the coloured species with 6-substituted HOA lies in the range of (0.52-1.5) x 106 1/mol cm. Of these the simplest compound, N-hydraxy-NtN'- diphenyl benzamidine (HDPBA) gives the most sensitive colour reaction. No interference of diverse ions was noticed. The method was applied to the determination of V in different environmental samples.

Bromo pyrogallol 640 nm The new colour forming system V(V)-BPR-CPB- 418 Red (BPR), Hexadecyl «=100000 D CTA in NH3.H20-N H 4C1 buffer soln. of pH pyridlnium bromide 8.0 to 9.0 has been studied. V(V) forms a (CPB) and Cyclohexane multicomponent complex in the presence of D diamine tetra acetic C TA . B eer’s law is obeyed fo r 0 to 12/¿g V (V )/25 acid (D CTA) ml. A recommended procedure was applied to the determination of micro amounts to V in geological sam ples. X. o r R em arks R efs. N am e o f th e R eag en t max. w orking wavelength w ith e

N-Benzoyl-N-phenyl- 595 nm 5 to Vanadium (V) reacts with cited reagent in 5-7 M- 419 hydroxyl amine e= 4 4 0 0 7M - H3P04, and 40 to 60% acetone (ethanol, H PO propanol, dioxane, butanol) to form a complex 3 4 soln. The method has been applied for determination of V in iron, nickel and Ti base alloys. o-Phenanthroline 510 nm A cidic Micro amounts of V were determine^ in steel, 420 iron and iron alleys by pptn. of Fe3+ with NaOH; after filtration, the filtrate was acidified with H JS04 and excess Fe2+ was added. In acidic soln. Fe + reacts with V5+ to produce Fe3+ and V4+; in ammoniacal soln., the reverse reaction occurs to produce v and Fe . The reagent reacts with Fe*+ to form a complex and, from the amount of Fe2+ produced, the amount of V was determined indirectly; the complex was stable for one day. l-Phenyl-3-methyl- 490 nm 2.5 Vanadium (V) was extracted from aq. solns. (pH 421 2-benz-5- to 2.5 to 4.5) by adding PMBP soln. in chloroform: pyrazolone (PMBP) 4.5 butanol (4:1) and absorbance of the extract was measured. Tolerance limits of common ions were studied. V was determined in water and rock sam ples. N-Phenyl-l-methoxy- 540 nm 2.25 A new chromogenlc reagent (PMHNA) was syn­ 4 2 2 2-naphthoy) hydroxamic to thesised and used for determination of V in 2.25 to acid (PMHNA) 4.50 4.50 M-HCL The method was applied for the M-HCL analysis of titaniferous iron ores and slags. Relative error was < 5.21%.

Eriochrome Cyanine R 575 nm 4.7 Vanadium (TV) is extracted with N-phenylbenzo- 423 (ECR) and Cetyl- *=68100 hydroxam ic a d d in to CHC13 an d th en back trimethyl ammonium extracted with 0.1 M NaOH with simultaneous bromide (CTAB) reduction of V(V) to V(IV) in buffer medium (pH 4.7) by ascorbic add and formation of a ternary complex with (ECR) and (CTAB). Addition of CTAB improves sensitivity. The method was applied to determine 0.05 to 0.8 ftg/ml of V in Ni alloys.

C affeic acid (I) 370 nm A selective method for determination of ftg quan- 424 and Aliquat 336 (II) e - 13000 tities of V(V) is described. The complex V(V)-I-II is yellow and the method is compared with the atomic absorption spectrometric method and applied to trace determination of V in steel, alloys, a rock and environmental samples.

Phenyl fluorone (I) 550 nm 8.8 Vanadium (V) reacts with (I) in presence of (II) at 425 and Cetyl pyridinium « = 7 .0 x l0 4 pH 8.8 to form a 1:2 vanadium-(I) chelate. The brom ide (IQ sensitivity index is 0.7 ng/cma. Beer’s law is obeyed up to 037 ppm of V. The interference of other metal ions is eliminated by electrolytic separa­ tion using a mercury cathode; The developed method was applied for the determination of V in steels. R efs. M icro am ounts o fV in M oO aw ere determ in ed 428 The method is based on catalytic action ofV(V) 427 Tween 40. Thepresence complex was ofstable 20 for mg 2 hr.Mo8+, In thethe linearity between R em arks A ternary complex is formed byabsorbance reaction of V(V)isthe stable complex for is in V:I:II2 thehr. range=The 1:1:2. composition 4260 Beer'sto 20 /tg lawof isV/25 obeyed ml. The method was on oxidation of thereaction reagent is by followed bromate, by which measuring the rate of absorbance andconcn. concn. range of V 0 was to observed 6 /tg/25 in the ml. A mathematical with I and II and pH 7.5 borate buffer soln. The applied for determination of V in Ag-V ores. range 10 totangent 400 method ng/mlatm. was usedcan for particulate bedetermination determined. of V matter, inThe human serum and with DAVPM in presence ofH3P 04, Mn2+, and yields a red-violet complexchange in acidic in absorbance medium. The at 30*. Vanadium (V ) in the synthetic mixtures. 4 3 7.5 acidic H PO e= 81000 500 nm 545 nm 550 nm \ n a x . o r p H w avelength w ith e w orking 1,4-Dihydroxy bromide (II) bis(Antipyrin-4-yl) methane (DAVPM) phthalimidedioxime Phenyl fluorone (I) Name of the Reagent phenyl-vinyl and Cetyl pyridinium

198 method for correcting the effect of matrix Mo in the determination is described, which consisted of measuring the absorbance effect due to 5 /¿g V in presence of various amounts of Mo.

N-Phenyl acetyl- 510 nm 4M- Vanadium forms a complex with cited reagent in 429 mandelo-hydroxamic e= 18200 HC1 4M-HC1 and the red-violet complex is extracted acid. into CHC13. Procedure: (1) mixing of a sample with concentrated HgS04, evaporation of liqs., calcination at 525*, and digestion of the inorganic residue for 15 min. with aq. HC1; (2) adding a few drops of concentrated HNO„ and H SO and heating until while fumes are formed; (3) neutralization with aq. NHa; and (4) dilution to 50 ml with H2O.HCl (12 M) is added to an aliquot containing 20 to 135 fig V, and the sample is brought to a final vol. of 50 ml; 10 ml of CHClg containing 10"2 M-I is added, the sample is shaken, and the organic phase is dried over NagS04. Beer’s law is obeyed at an aq. concn. range 0.3 to 30 jug/ml, the optimum concn. range is 0.4 to 2.7 fig /m l with a detection limit of 0.2 /ug/ml; the relative standard deviation is 1.6% (for detns. on samples containing 2.1 jug/ml). Comparisons of analysis of V content of Arabian Medium Crude petroleum with this method were within 5% of a vo VO standard (ASTM, based on phosphatotungsto- vanadic acid formation) method. REFERENCES

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