Review of Fundamental Developments in Analysis Electroanalysis and Coulometric Analysis Allen J. Bard Deparfment of Chemisfry, The University of Texas, Austin 72, Texas

RIS review mainly surveys the ods. The application of coulometric ing irreversibility with time to “aging” Tliterature during 1960 and 1961, (and other electrochemical) methods to of the oxide film. Both papers (113, and is patterned closely after previous analytical problems in atomic energy 170) assume that the reduction of oxy- reviews in this series. Papers published work has been rebiewed (136). The gen proceeds via a direct chemical re- before 1960 which have not appeared in reviews by Barendrecht (14) (66 refer- action between and platinum, previous reviews have also been in- ences) and Morris (137) (161 references) followed by electrochemical reduction of cluded. Research has increasingly been on coulometry, as well as one by the platinum oxide(s). Apparently the concerned with a study of the funda- Meites (130) on the application of con- rate or extent of the platinum-oxygen mental electrochemical principles upon trolled potential electrolysis to electro- reaction in an acidic solution is suffi- which electroanalytical procedures are gravimetry, coulometry, and synthesis, ciently small that a prereduced electrode based. The discussion of these theo- deserve mention. Other reviews on in an oxygen-saturated solution will retical electrochemical developments various phases of coulometry have also maintain the characteristics of a re- has been limited to areas which have the appeared (39, 110, 146, 183). duced surface. most direct bearing on electroanalysis. Anson has recently found that the As a general trend of the past two years, ELECTROCHEMICAL THEORY reversibility of both the reduction of coulometry continues to enjoy increas- (II1) and the oxidation of iron(I1) ing development and application, while Platinum Oxide Films. h topic is markedly decreased by the presence of classical electrogravimetry has mainly which continues to enjoy attention is an oxide film on the electrode (4). He been concerned with extension of pre- the effect of oxide films on electrode further showed that some effects hereto- viously developed methods. reactions occurring at platinum elec- fore ascribed to the presence of an oxide trodes. Previous work concerned film are actually caused by a film of BOOKS AND REVIEW ARTICLES with the evidence for oxide films platinized platinum formed when an on platinum electrodes has been oxidized electrode is reduced. It is The book of Charlot, Badoz-Lam- reviewed by Laitinen and Enke (108). this platinized platinum (rather than bling, and Tremillon (33)discusses elec- These authors also present new experi- platinum oxide) n-hich increases the trochemistry from the viewpoint of the mental work on the oxide films and reversibility of many electrode re- analytical chemist. Extensive use is offer possible mechanisms for their actions. Contrary to some reports, made of current-potential curves for formation. Khile the existence of Anson believes, as a general rule, that explaining the basis of the various oxide films is undisputed, the effect of oxidation of a platinum electrode pro- techniques. Chapters on coulometry, these films on electrode reactions re- duces a decrease in the reversibility of potentiometry, amperometry, and non- mains controversial. Davis (40) oxidations occurring at the rlectrode. aqueous solvents, as well as an extensive studied the variation of the rate con- The nature of the electrode surface also bibliography, are included. Reinmuth stant, k, and the transfer coefficicnt. CY, affects rates of organic electrode re- has written a chapter on the theory of of reactions occurring at a platinum actions (22). electrode processes for the new series electrode, with the extent of electrode Other factors may certainly affect the “Advances in Analytical Chemistry and oxidation. He concluded that a heavy behavior of platinum electrodes, and the Instrumentation” (160). The text of layer of oxide suppresses the rate of an absence of these effects must be assured Laitinen (IO?’) includes a chapter on electrode reaction, but a film about 1 before oxide film effects are invoked. electrolytic separations and electrolysis, monolayer thick increased the rate of Adsorption of surface active agents on which gives a brief, but particularly such electrode reactions as the oxidation an electrode is know to affect the rate lucid, discussion of the fundamental of arsenic(II1) or the reduction of of some polarographic reactions (160), principles of electrolysis. Controlled (V) , vanadium(VI), oxygen, and similar effects on platinum elec- potential electrolysis, as applied to or- and iodate ion. Anson previously had trodes must be expected. Formation ganic chemistry, has been reviewed by shown that iodate reduction proceeded of metal hydrous oxide films when an hIeites (131). Tetter has given a more reversibly at oyidized electrodes electrode is cathodized may aflect modern treatment of electrochemical (6). Linganc demonstrated that an electrode behavior. Even the orienta- kinetics in his recent book (207). A oxide film hinders the oddation of tion of the electrode cystallites can welcome addition to the growing list of oxalate ion (112), but is necessary for affect the rate of electrode reactions. chemical journals is the Journal of the reduction of oxygen (113). So Xikulin (149) recently showed that the I

VOL 34, NO. 5, APRIL 1962 57 R processes. A knowledge of the elec- ELECTROSEPARATIONS (189); the separation of In from Fe trode reaction mechanism is funda- (172); the separation of Co, Si, and mental to the application of electro- Electrolytic separation of radioactive Cu from Pu (16); and the separation analytical techniques such as controlled isotopes by deposition on mercury or of Sb and Sn from large amounts of potential coulometry to organic deter- solid electrodes continues to enjoy Zn (9). minations. Many, if not most, organic application. Polonium was separated An interesting method for the deter- electrode reactions involve the addition from other metals on a platinum or mination of gases in metals is based upon or abstraction of a single electron as a cathode (1). An internal the liberation of a gas upon anodic primary step, causing the formation of electrolysis method for separation of dissolution of the metal (100). The a free radical. The presence of an polonium has also been described (204). determination of in steel is unpaired electron on this radical sug- B study of the effect of current density described. The method was also con- gested the use of EPR as a means of and various solution conditions on the sidered applicable tu the determination identifying extremely low concentra- electrodeposition of tracer quantities of of nitrogen, but oxygen determinations tions (lop8 to 10-9M) of intermediate the actinide elements from an XH4C1- would probably require dissolution in a radicals, vihich usually continue to react HCI system n-as made by Mitchell (136). nonaqueous medium. in various secondary reactions. The A similar study lvas performed by Samartseva (168). Plutonium was sep- first applications of the electrogenera- ELECTROGRAVIMET RY tion of radicals inside the cavity of an arated by deposition on a tantalum disk EPR spectronieter were made by Maki cathode (214). The separation of ra- Reinmuth (161) has shown that a and Geske (118), who presented evi- dium and barium at a mercury cathode three-dimensional representation of the dence for the production of 'C104 by a constant current technique has reversible deposition of a metal on radical during the electro-oxidation of also been described (102). a solid electrode (plotting potential, lithium perchlorate in acetonitrile. In Further investigations of the elec- current, and percentage deposited) is a subsequent paper (56) they described trolytic separations of the rare earth useful in teaching the theory of elec- the electrogeneration and EPR spectra elements have also been made. Lan- trodeposition. of the nitrobenzene anion radical, a thanum-140 of 99.9% purity was pre- Controlled Potential Methods. The fairly stable radical, and resolved the pared by constant current electrolysis Japanese investigators continue to spectrum into the full 54 hyperfine of a Ba140-La140mixture in a perchlorate work on electrolytic analysis in the components expected. The EPR spec- ion medium at a platinum cathode (64). presence of chelating agents. Tanaka tra of radicals generated from a number More frequently separations are made (198) studied the deposition behavior of substituted nitrobenzenes have sub- at mercury or amalgam cathodes. The of Au, Ag, Hg, Cu, Bi, Sb, Pb, Cd, Sn, sequently been described by Geske and effects of current density and solution Xi, Co, and Zn at several pH's from Maki (56, 119, 120). Other electro- conditions in the separation of Ce144, solutions of ammonium nitrate, chloride, generated radicals observed by EPR Pr144, and Ho'~~were investigated (167). or acetate and varying amounts include the p-phenylenediamine positive The electroseparation of europium has of (ethylenedinitri1o)tetraacetic acid ion radical (I%), tetracyanoethylene also been described (181). Onstott has (EDTA). illthough all of the metals, derivatives (162), N-alkylpyridine rad- continued his investigation of the except Ni, Co, and Zn, were deposited icals (173),and aliphatic nitro-negative separation of the lanthanons at amalgam at the cathode, only Cu, Cd, and Ag ion radicals (154). Most work on the cathodes; especially by reduction at were deposited quantitatively. Fur- electrogeneration of radicals was per- lithium amalgam cathodes in a citrate thermore, the deposited metals were formed in nonaqueous solvents, such medium (148). In general, lanthanons found to contain considerable amounts as acetonitrile, dimethylformamide, or showing a I1 ohidation state (Eu, Sm, of EDTA, leading to positive errors. 1,2-dimethohyethane (glyme) (861, Yb) are easily separated from those that Nakagawa (140) investigated the ap- mainly to avoid the large dielectric show only a 111 state; so that separation plication of diethylenetriaminepenta- losses of water and other polar solvents of Yb from Tm at pH 6 allows prepara- acetic acid (DTPA) to the determina- in the EPR cavity. By using a spe- tion of 99.98% pure Yb (149). The tion of Cu in the presence of Bi, Sb, cially constructed sample cell (nom more difficult separation of a pair show- and As. The recommended procedure commercially available) and 100 kc. per ing only a 111 , Nd and involves electrolysis at 70" to 80" C. at second field modulation, Piette, Ludwig, Pr, has also been made (147'). a potential of about -0.50 volt 1's. and Adams were able to obtain spectra Sayun and Tsyb (171) deposited S.C.E. from a solution containing in aqueous solutions (153, 16Q), which In, Zn, Cd, and T1 with a constant DTPA, citrate or tartrate, and hydra- aided in the elucidation of several current at a mercury electrode. The zine. A procedure for the determina- electrode mechanisms. Recently Bard resulting amalgam was removed, and tion of Zn in the presence of Xi in an and Mayell used EPR spectroscopy to the elements, stripped into 1Jf HzSOa EDTA medium is also described (140). confirm a free radical intermediate in with a constant current, were deter- The determination of Cu (1S9), as the electroreduction of quaternary am- mined titrimetrically or polaro- well as Zn (199) and Pb and Sn (165), monium compounds (IS). Various dif- graphically. The potential of the mer- in copper alloys by rather conventional fusion and kinetic considerations in the cury pool was monitored and the methods has been reported. Alfonsi EPR spectroscopic detection of elec- stripping ii-as halted at various po- (3) has continued his investigations of trogenerated free radicals were discussed tentials to obtain separations of the electrogravimetric determinations of by Geske (55). Continued interest metals. Obviously a potentiostatic nonferrous alloys by describing methods in the mechanism of organic electrode stripping procedure would be simpler. for the determination of Cu, Pb, Sn, reactions will lead to further application The controlled potential electrolytic and Sb in Pb- and Sn-based alloys. of EPR (and also visible and ultra- removal of interferences prior to a Kovalenko stressed the importance of violet) spectroscopy to the detection determination of 110 was studied (160). potential control in the electrogravi- and identification of free radical inter- The separation of small amounts of metric determination of Bi (103). The mediates. It is possible that elec- Ag, Cu, Bi, and Hg in biological stability of the potential of a saturated troanalytical techniques for the deter- materials by an internal electrolysis calomel electrode when employed as an mination of trace quantities of organic technique has been described (43). anode in controlled potential electrolysis substances by EPR spectroscopic ob- Other separations reported include the mas investigated by Hayakawa (69). servation of electrogenerated radicals separation of Cu in bronze analysis Controlled Current Methods. In- may be devised. (82); the separation of Fe from Zn terest in controlled current (or "con-

58 R 0 ANALYTICAL CHEMISTRY stant current”) electrogravimetric lometry” should be discouraged. Craig for the controlled potential coulometric methods in the presence of EDTA et al. (38), at the National Bureau of determinations of metals seems promis- continues. Nakagawa (140) deter- Standards, have redetermined the value ing, and should be especially useful in mined Cd in the presence of Zn from an of the faraday as 96,490.0 =t2.4 coulombs cases where the product of the electrode EDTA solution, Containing gelatin as a per equivalent (chemical scale) by reaction reacts with water. AIBthB, brightener, maintained at a pH of 3.5 measuring the weight loss of a silver Cs&thy, and Richter (123) determined to 4.0 with a citrate buffer. Zinc could anode during electrolysis in a perchloric (II1) by oxidation to Cr04-* be determined by then making the acid medium. This value is in very in 5X KaOH at 0.35 volt us. S.C.E. solution strongly alkaline, converting good agreement with the one previously From 1 to 17 mg. of Cr could be deter- the Zn-EDTA complev to ZnOn-2, determined by electrolytic o\idation mined with an average error of 1%. which is electrolytically deposited. of sodium oxalate. Several different Duncan has reported the determina- Hayakawa (68) n.as able to deposit electrode materials which have been tion of nitrate ion at a mercury cathode Bi quantitatively at a platinum cathode used for electrolysis might find ap- at -1.0 volt vs. S.C.E. (44). The from EDT.1 solutions of pH 3.5 to plication to coulometric methods. reduction proceeds quantitatively to 53. Lead could also be determined These include boron carbide (I%), nitrogen gas in the presence of uranium under similar conditions, at pH of 6 silicon (is), and germanium (54) elec- (111), which acts as a catalyst. Only to 7. These results appear to dissgree trodes. zinc and substances mhich complex with the conclusions reached by Tanaka Controlled Potential Coulometry. uranium are said to interfere, and 0.1 (198) concerning depositions from This technique continues to find to 0.5 mg. of nitrate can be determined EDTA&solutions (see above). Haya- application for the determination of with a standard deviation of kO.5%. kawa determined Ag and Hg (on a the actinide elements, especially in Kulandaivelu and Nair (106) have silver-plated platinum cathode) from nuclear fuels. Modifications of pre- determined ferricyanide ion by pre- EDTrl solutions (70). viously described methods for the cipitation with silver ion formed by Vernon (206) also determined Hg, determination of uranium ($8,78, 186, controlled potential oxidation of a silver iii organomercury compounds, after 2W0), plutonium (66, 174, 180), and anode at 0.32 volt vs. S.C.E. in an dissolution of the compound in an neptunium (186, 187) have been pub- acetate buffer, pH 5. Analysis of 35 ethyl alcohol-sodium sulfide mixture. lished. to 70 mg. of ferricyanide can be per- Foster and Williams (511, in agreement Davis determined iron(II1) and ce- formed nith an average error of =:0.6%, with previous workers, found that cath- rium(1V) by reduction at a platinum in the absence of chloride and other odic deposition of Co leads to high cathode in IJd sulfuric acid (39). The ions which precipitate with silver ion. results because of simultaneous deposi- solution containing Fe and Ce was This same reaction has been used for tion of some oxides. Yokosuka first ovidized at a potential of 1.5 volts a conctant current coulometric and Morikawa (218) reported similar vs. S.C.E. X new platinum electrode, of ferricyanide (152) (see belon-v). findings, but shoived that the deter- pretreated by immersion in a 0.01X Foresti described an improved ap- mination of Co was accurate when ceric ion solution, was introduced and paratus for the coulometric determina- deposition was made from a Na4P407- ceric ion was reduced at 0.80 volt, tion of hydrogen (50). NHIOH or (NH4)C03-SH40H medium. followed by ferric ion at 0.20 volt. A Controlled potential coulometry con- The duration of electrolysis under these new, pretreated, electrode was necessary tinues to find application to the analysis conditions was about 20 hours. Kobal so that reproducible corrections could of organic compounds. Ascorbic acid (101) reported that the determination be made for the reduction of the was oxidized in a 2-electron process at a of Cu is inaccurate in the presence of platinum oxide(s) which occurs si- platinum anode in a potassium acid large amounts of Fe. The application multaneously with ferric ion reduction. phthalate buffer, pH 6, at 1.09 volt of Kinkler electrodes to several elec- The determination of 0.15 to 0.8 meq. vs. S.C.E. by Santhanam and Krishnan trogravimetric determinations has been of Fe and Ce was carried out with an (169). This reaction was made the dcscribed (84,85). average error of 1.0.370. The con- basis of a coulometric determination, Internal Electrolysis. Lipchinski trolled potential coulometric determi- and 15 to 100 mg. of ascorbic acid were and fordanov (115) determined hIn by nation of tin(1V) has been reported by determined with an average error of anodic deposition of l\lnOz.HzO on a Bard (11). Reduction occurred in two 10.7 mg. Citric, succinic, and tartaric platiniim anode from an acetate buffer, steps in a 3M NaRr-0.3-11 HC1 medium, acids do not interfere nith the deter- pH 4.5, at 80” C, The cathode was first to tin(I1) (-0.40 volt us. S.C.E.), mination. Takiura, Masui, and Say0 graphite immersed in a PbOz-NanSOd and then to tin amalgam (-0.70 volt) determined a-hydrosyaniino derivatives paste contained in a ct~lluloseSoxhlet at a mercury pool cathode. Deter- of several fatty acids by reduction at a thimble coated iyith collodion. Cad- minations of 20 to 50 mg. of tin based mercury electrode at pH 2 (197). The mium and Bi were plated on a platinum on the second reduction step were electrode reaction is the 4-electron cathode using a Zn- or Fe-plated performed with an average error of reduction of the =S-OH group to platinum anode separated from the about 0.3%. Tise and Coksl deter- --SHz, to form the corresponding amino catholytc by a sintered-glass disk (219). mined europium(II1) and ytterbium acid. (111) by reduction to the divalent ions Several papers have appeared which a mercury cathode (916). Because describe coulometric analysis employing COULOMETRY at the divalent ions of Eu and Yb tend internal electroly~isfor potential con- Attention is directed to the sug- to react with water, causing an apparent trol. This method seems attractive, gestions of Delahay, Charlot, and current efficiency of less than loo%, since a potentiostat is not needed, and Laitinen ($1) concerning the classifica- the determination was carried out in analysis can be performed by short- tion and nomenclature of electro- absolute methanol, employing 0.lX curcuiting the electrolysis cell through a analytical methods. In particular they tetrabutylammonium bromide as a necessarily low-resistance coulometer. suggest that the term L‘~~ulometri~supporting electrolyte. Only the sum Xiwa and Rlusha (143) determined Ag titratien” be reserved for controlled of Eu and Yb can be determined by this by depositing it on a gold electrode, us- current coulometry, or, in general, to procedure, but Eu itself can be deter- ing a Bi amalgam anode. These processes involving the electrogenera- mined in aqueous solution by a pre- authors also determined Bi, in the tion of a titrant. The practice of some viously described reoxidation procedure. presence of large amounts of Pb or authors to use this term for what is more The use of such nonaqueous solvents Cd, by depositing it on an amalgamated precisely “controlled potential cou- as acetonitrile and dimethylformamide Cu electrode, employing a Pb amalgam

VOL. 34, NO. 5, APRIL 1962 59 R anode. Average errors in both deter- requires the determination of a calibra- BROMISE. Bishop described the minations mere about h3%. The tion curve, since current, rather than titration of microamounts of hydrazine total amount of electricity required for coulombs, is the quantity actually (81). Using two-electrode poten- the depositions was determined by measured. Shults has described a cou- tiometric end point detection, and cell integration of recorded current-time lometric titration of plutonium(V1) volumes of 50 to 500 ~l.,5 X lO-l0 to curves. Both Lipchinski (114) and with iron(I1) formed at constant poten- mole of hydrazine was determined Kis and Sheitanov (97) describe oxida- tial in 1-It sulfuric acid (179). In this with errors of =t5 to 10.1%. Olson tion of iodide by an internal electrolysis technique, a platinum electrode is also titrated hydrazine and substituted procedure. The latter authors, em- maintained at 0.27 volt us. S.C.E., and hydrazines, employing an acetic acid- ploying a platinum gauze anode and a the Pu and Fe are reduced to the I11 and methanol mixture, and mercuric acetate Pb02-H2SO, paste catholyte, deter- I1 osidation states, respectively [an as a catalyst (145). Although most mined 30 to 100 pg. of iodide with an excess of iron(I1) is necessary to com- monosubstituted hydrazines consumed average error of =t3%, The cou- plete the reduction of plutonium(V1) 1. four equivalents of bromine, asym- lometric determination of hydrogen by Uraniurn(S‘1) is not reduced at this metrically disubstituted hydrazines con- oxidation at a platinum anode, em- potential. The potential is increased sumed six equivalents. Employing ploying a potassium peroxydisulfate to 0.66 volt, whereupon oxidation to two-electrode amperometric end point solution as a catholyte has also been iron(II1) and plutonium(1V) occurs. detection, milligram amounts of the reported (178). The net result of this reduction and hydrazines were determined with a The application of controlled poten- oxidation procedure is the reduction of standard deviation of il%. The tial coulometry to the study of mech- plutonium(V1) to the IV state. This determination of several substances of anisms of electrode reactions has been method will be useful only when one pharmaceutical interest, including discussed by Bard (12). Mechanisms couple [in this case plutonium(V1)- antipyrene (19O), thymol (869, thio- involving secondary electrode reactions plutonium(1V) ] is electrolyzed ir- pental sodium, and rivanol (191) have following the primary electrode reac- reversibly. In many cases an auspi- reported. Additional applications of tions are common in organic electrode cious choice of a dual intermediate sys- bromine to the determination of olefin reactions, especially when the primary tem will allow the determination to be compounds (211, 612) have also been reaction involves the formation of a performed by a constant current cou- made. Iodide, which previously has free radical. An example of a reaction lometric titration. The reported ac- been titrated to the I state in strongly of this type is the electroreduction of curacy for the determination of Pu was acidic solution, was oxidized to iodate quaternary ammonium salts discussed only about 2%, probably because of at pH’s of 2.8 to 4.5 by Berraz and by Bard and hlayell (IS). Rechnitz some oxidation of the platinum electrode Delgado (18). These same authors also and Laitinen studied the reaction of itself during the reoxidation step. describe titration of metallic 8-quino- (V) with perchlorate ion RuiiEka has presented an interesting lates by a modification of a previous by performing the electroreduction of combination of isotope dilution measure- procedure (17’). Although the titration molybdenum(V1) at a mercury electrode ment and electroanalysis (166, 166). of iron(I1) with bromine has been in the presence of C104-, an example of To determine Ag, the unknown amount reported (196), the errors of the deter- a catalytic reaction (158). Several of silver(1) in the sample is mixed with mination are so large (5 to 7%) that the unpublished applications of this method a knoii n amount of radioactive Ag. titration with (47, 94) appears have also been mentioned in a recent The Ag is deposited on a platinum elec- preferable (see below). review article (130). trode in a cell connected in series with CHLORIXE.Two of iron Badoz-Lambling discussed the origin one which contains only the radioactive (11) have been reported. The method of the residual current in controlled silver. Since equal total amounts of Khakimova and Agasyan (94) em- potential coulometry with reference to of Ag are plated on the cathodes of ployed potentiometric end point detec- the oxidation of bromide ion (8). both cells, the ratio of radioactivities tion for the determination of microgram MaSek advocated the use of a separate of the cathodes is a measure of the Ag amounts of Fe. Farrington, Schaefer, reference electrode in millicoulometric content of the unknown. The cell and Dunham (47) found that copper(I1) determinations (122). containing the known amount of radio- is a catalyst for the iron(I1)-chlorine Several modifications of controlled active Ag functions essentially as a reaction, and determined 500 fig. of Fe potential coulometry have been pro- “radioactivity coulometer” (165). This in 50 ml. of solution Kith an average posed. A technique described as “volt- method is especially useful for the error of h0.1% employing one-electrode age scanning coulometry,” which in- determination of very small amounts of amperometric end point indication. volves the slow variation of the poten- metals, since plating need not be Titrations of thallium(1) (93), cyclo- tial through the region at which a quantitative, and loss of sample by hexal, and hexobarbitone (89) with substance is reduced or oxidized, is said adsorption onto the cell walls does not chlorine have also been described. to give more reproducible residual cur- affect the accuracy of the analysis, as IODINE.Braman and coworkers (27) rent readings, and therefore is more use- long as it affects both the stable and described a coulometric borane monitor. ful for determining very low concentra- radioactive isotope to the same estent. The boranes are titrated with iodine tions of substances (175). By this Using this technique, amounts of silver until the two-electrode amperometric technique, reduction of iron(II1) sam- of 1 to 100 pg. mere determined with detecting system indicates a preset ples of 0.025 to 5 pg. was analyzed with errors of 0.8 to 2.3%. iodine level has been reached. In- a deviation of 3t0.02 wg. It is difficult cremental generation of iodine pre- Controlled Current Coulometry- to see why this method should give vented coupling between the generating Coulometric Titrations. Although more precise or accurate determinations and indicating electrodes. Determina- that constant potential coulometric applications of coulometric titrations tions of parts per million amounts of techniques. Meites has determined continue to increase, only cyanide ion boranes agree with colorimetric deter- 0.07 to 10 pg. of Zn, and by employing (6) and sulfhydryl compounds [ thiogly- minations to within 0.02 p.p.m. Sulfur careful background current corrections colic acid (133) and monothioethylene analyzersbasedon combustion of the sul- obtained an accuracy of about 0.007 glycol (ISg)] may be listed as new fur-containing compounds and titration pg., using conventional constant poten- coulometric titrants. The classifica- of the resulting SO2 with iodine (74) tial procedures (129). Moreover the tion of coulometric titrations given have been reported (49,58). Titrations voltage-scanning technique involves below is based upon the electrogenerated of tin(I1) (SO) and thiamine hydro- more complex instrumentation, and titrant employed. chloride (90) have also been described.

60R ANALYTICAL CHEMISTRY CERIClox. Takahashi and Sakurai Crz(S04), medium at pH 3 to 4 (83). through the paper is a measure of the determined a number of organic com- Although the current efficiency for the COZ concentration. To ascertain the pounds, including 2-naphthylamine, an- electrogeneration of chromous ion was ultimate practical precision of cou- iline, phenol, oxalic acid, D-mannitol, not investigated, the titration efficiency lometric titrations, Taylor and Smith and D-sorbitol by generating an excess for the determination of 4 to 40 Mg. of (200) titrated several acids in a cell of ceric ion, and back-titrating with oxygen, employing potentiometric end designed to eliminate interchamber electrogenerated ferrous ion (195). The point detection, was close to 100%. An transfer, using a quartz crystal con- rate of oxidation of quinol and p- application of the previously described trolled time-interval meter and ac’curate aminophenol by ceric ion was so rapid titration of ferric ion with electrogener- measurement of current. These au- that they could be titrated directly, but ated titanous ion to the determination thors give an excellent discussion of the the reported titration efficiency was of Fe in silicate rocks has been reported errors and precision of measurements in only 90 to 95% (194). A modification (34)* coulometric titrations. In general, the of the uranium(1V) titration, employing PRECIPITATIONAND COMPLEXATIOK. standard deviations and errors of the urea to eliminate interference of nitrate Xliller and Hume have introduced titrations were within 0.003%. It ion, has been reported (62). electrogenerated sulfhydryl compounds should be noted that for most cou- MAXGAXESE(III).Although incon- to the list of coulometric titrants lometric titrants, the deviation of the trovertible evidence has been presented (133, 134). Both thioglycolic acid and current or titration efficiency from 100% that nianganese(I1) is oxidized to monothioethylene glvcol are generated will be the most serious limitation to (II1) under the usual con- at a mercury cathode by reduction of very high accuracy. ditions of coulometric titrations (176), the corresponding mercury(I1) complex. NONAQUEOUSSOLVEKTS. Interest in some authors still persist in describing The compounds behave as both com- coulometric acid-base titrations in non- these as titrations with electrogenerated plexing agents for metsls and strong aqueous solvents continues. Mather “permanganate ion.” Fenton and Fur- reducing agents. Using a mercury and Anson (124) have titrated fluoride man ($8) independently studied the indicator electrode, the determination ion, in acetic anhydride containing a oxidation of manganous ion in sulfuric of Hg, Au, Cu, and ferricyanide by small amount of acetic acid, with hydro- acid- media at both thioglycolic acid (I%), and Hg, Au, Cu, gen ion generated at a mercury anode. gold and platinum electrodes, and Pt, and Pd with monothioethylene The end point was determined poten- reached conclusions similar to thcse of glycol (f34) has been described. An- tiometrically with either a glass or Selim and Lingane (176). Tutundii6 other report of a titration of Zn with amalgamated gold indicator eledrode, and Paunovi6 described the titration of electrogenerated ferrocyanide has been and a mercury-mercurous acetate ref- hydrogen peroside (201), iodide, and given (2). erence electrode. From 8 to 88 Meq. ferrocyanide (202) with electrogenerated Electrogenerated argentous ion has of fluoride ion were determined with an manganese(II1) employing poten- been used for several titrations. Paun- accuracy of 2 to 3%. The mechanism tiometric end point detection. ovid (162) described the titration of of the electrode reaction, and the cause FERRICYANIDE.Titration of chro- ferricyanide, employing two silver elec- of the lack of success when a platinum mic ion to Cr04-2 in a 5M NaOH, trodes for amperometric end point generator electrode was used, was also 0.1 to 0.2-71 K3Fe(CN)6medium, em- detection. Coulometric titrations of investigated (125). Interest also con- ploying 2-electrode amperometric end bromural and cabromal, compounds of tinues in coulometric acid-base titra- point detection, allowed the deterniina- pharmaceutical interest, have also been tions in acetonitrile (20,205). tion of milligram amounts of Cr with an described (87). A device for the auto- Eonaqueous solvents also seem prom- error of 1% (123). matic determination of C1 in organic ising as media for oxidation-reduction REDUCTANTS.ICies and Buyk ti- compounds, based on the automatic titrations. Although no comparable trated periodate with electrogenerated combustion of the sample and titration coulometric titrations have been de- ferrous ion (96). In solutions contain- with argentous ion, has been reported scribed to this writer’s knowledge, ing 0.1 to 0.2N sulfuric acid, periodate (37). Kies has expanded his titration several recently reported methods, in- is reduced to iodate, so that iodate of thiourea with electrogenerated mer- volving iodimetry (42) and cerimetry itself, ei.en in very large amounts, does curic ion to a number of hi-substituted (157) in acetonitrile, and titrations with not interfere in the titration. Ap- thioureas (95). titanous and chromous ions in dimethyl- paratus has been devised for con- Electrogenerated cyanide ion, re- formamide (76), should be adaptable to tinuously and automatically measuring ported by hS011, Pool, and Wright coulometric titrations. Liu has de- the chlorine concentration in bleach (6), is a welcome addition to the ranks scribed the coulometric titration of solutions, containing between 20 p.p.m. of coulometric titrants. Cyanide ion copper (I) with palladium( 11) generated and 3% chlorine, by continuous cou- was generated by reduction of Ag- at a palladium anode in a Li2S04-K2S04 lometric titration R-ith ferrous ion (CN)*- at a platinum cathode in a fused salt eutectic (116). Two modifi- (46). The magnitude of the current, solution containing 0.01M NaOH and cations of the coulometric Karl Fischer which is a measure of the chlorine con- 0.2531 K*Ag(CY),. The determination titration have been described (15, 144). centration, is continuously adjusted to of milligram amounts of silver(I), MISCELLANEOUS.Hanselman and maintain the potential of an indicator (II), and gold(III), using two Rogers have published their previously electrode near the equivalence point silver electrodes for potentiometric reported method of “generating” rea- potential of the iron(I1)-chlorine reac- end point detection, has been described. gents by passage through ion exchange tion. Electrogenerated stannous ion ACIDS AXD BASES. Several papers membranes (67). In this technique a has been employed in the titration of describe the determination of boron by solution containing the ion that one platinum(1V) (10). The titration reac- formation of boric acid, and titration wishes to generate is contained in a tion involves reduction of platinum(1V) with electrogenerated base in the pres- cell separated from the titration cham- only to the I1 state probably because of ence of mannitol (81, 151, 217). Small ber by an ion ehchange membrane. the slow rate of reaction between tin(I1) quantities of COI were determined by The production of anions-e.g., OH-- and platninuni(I1). Using poten- adsorption onto filter paper impregnated at the cathode will force solution anions tiometric and spectrophotometric end with barium hydroxide and phenol- through the membrane and into the point detection, milligram amounts of phthalein and held between two silver titration cell. The auyiliary electrode Pt could be determined with an error electrodes (156). The time required may be contained in the titration cell, of +0.5%. Chromous ion has been for the disappearance of the red phenol- or in a separate, third, chamber. used to titrate oxygen in a KCl- phthalein color while current is passing Generally, considerable deviation from

VOL 34, NO. 5, APRIL 1962 61 R 100% “current efficiency” results from oscillator and counter as a timing source LITERATURE CITED interdiffusion, incomplete selectivity of for coulometric titrations is free of (1) qbramova, L. I., Ziv, D. M.,RaGio- the membranes, etc., and the accuracy start-stop errors and is capable of high khamiya Analiz Produktov Delenzya, is only fair. The technique should be accuracy. Maekawa and Okazaki (117) Akad. Xauk S.S.S.R., Rndievyi Inst. useful in certain special cases. A have described a counter being used Znst. inz. V. G. Khlopina, Sbornik similar technique has been reported in a essentially as a coulometer, n-hich indi- Slatei, 1960, 93. (2) Agasyan, P. K., Vestrick Moskav. recent patent (61). cated the quantity of electricity con- Cniv. Ser. Mat., Jfekh., Astron., Fiz., i Some interest continues in the use of sumed irresprctive of the current level. Khim. 6, 156 (1959). coulometric titration detectors in gas A sill-er coulon~eterhas been recom- (3) Alfonsi, B., Anal. Chiva. dcta 22, 431 chromatography. Using variations of mended for a similar purpose in student (1960); 23, 375 (1960); 25, 274, 374 ( 1961 ), the technique described by Liberti LT-ork (20s). Several automatic coulo- (4) Anson, F. C., ANAL.Camf. 33, 934 (Ill), coulometric detection of halide metric titrators, based on previously 11961). ions 13 ith electrogenerated argentous described principles, have also been (5j Anson, F. C., J. Am. Chena. Soc. 81, ions and 802 nith bromine, from reported (7, 103, 193, 216). 1554 (1959). (6) Anson, F. C., Pool, K. H., Wright, halogen- or sulfur-containing com- Potentiostats. Descriptions of new J. M.,J. Electroanal. Chem. 2, 237 pounds has been described (88,69, 36, potential control devices. most of (1961). 98). Several coulometric (or ampero- which offer few advantages over (7) Anton, A., Mullen, P. IT., Talanla metric) oxygen gas analyzers, based on previously described ones. continue. 8, 817 (1961). (8) Badoz-Lambling, J., J. Electrochem. reduction of adsorbed oxygen on a Ag These include electromechanical types Chem. 1, 44 (1959). cathode, using Pb or Cd anodes have ($3, 72, 73, IYZ), operational aniplifier (9) iBagdasarov, K. S., Soobshcheniya o been reported (73,91,104). types (35, 92, 184> 210), and others A nuch, Rabot. Chlenov Vsesoquz. Khznz. Stripping Methods. Several addi- (69, 99). One which deserves notice, Obshchestm zm. Mencielecza 1955, No. 1, 15. tional methods for the determination however, is the simple apparatus devivd (10) Bard, A. J., Au~L.CHEV. 32, 623 of thin metal deposits by constant by Hickling (75). Hickling, who con- (1960). current anodic stripping have been structed one of the first potentiostats, (11) Bard, A. J., Anal. ChLm. Acta 22, reported. These include methods for presents a three-tube device capable of 5i7 (1960). (12) Bard, A. J , Southwest-Southeast Sn on an Fe base (105), Cr on steel delivering up to 300 volts at 0.3 ampere, Regional Meeting, .ICs, Kern Orlean?, (I%), Xi on Cu base (I&?), and .4g on and capable of controlling to *lo mv. La., December 1961 various substrates (127). Robson and with a response time of 10 milliseconds. (13) Bard, 4. J., Rlayell, J. S.,Division Kuwana found that boron, deposited on The control device is a beam tetrode, of Analytical Chemiatry, 140th Meet- ing, ACS, Chicago, Ill., September platinum, could be determined by a the grid of which is controlled by a 1961. similar technique (163). Boron was Schmitt trigger circuit. The cost is (14) Barendrecht, E., Chem. Weekblad. oxidized in a 3-electron step to borate said to be below $100, Two papers 56,37 (1960). ion. Sarayanan, Sundararajan, and dealing nith factors controlling the (15) Barendrecht, E., Il’ature 183, 1182 (1959 i Kasabekar (141) found an alternating design of potentiostats for the study (16) Bergstresser, K. S., U. S. Atomic current impedance change (rather than of the kinetics of electrode reactions Energy Comm. LA-1064, 22 pp. (1956). the usual direct current potential stress the interaction of the experimental (17) Berraz, G., Delgado, O., Rev. fac. change) could be used to indicate system and the potentiostat (19, 53). ing. qu‘lm: (Univ. nd.litoral, Sunfa-Fe, Arg.) 28,39 (1960). complete stripping of metals. Cou- Coulometers. Two titration coulom- (18) IbiJ/”U’) y.Tl ””.6‘2 lometric reduction of oxide films (24, eters, one using coulometric titration (19)~ Bewick, A., Bewick, A,, Fleisch- 164) and sulfide films (77) on copper (I@), have been described (188). mann, M., Liler, hl., Electrochim. Acta has also been described. Colorimetric coulometers, based on 1, 83 (1959). 20) Billon, J. P., J. Electroa~al.Chem. 1, Voorhies and Davis (208) described a optically measuring the changes in con- (1960). technique for the coulometric deter- centration of iodine (60) and copper(I1) ishop, E., filikrochim. Acta 1960, mination of substances adsorbed on (SI), have been devised. Bourgault 803. powdered carbon black. The carbon and Conway (65) devised an automatic (22) Bogdanovskii, G. A, Shlygin, A. I., Zhur. Fiz. Khim. 34,26 (1960). black was made an electrode, and the recording variation of a gas coulometer. (23) Borovkov, V. S., .4verbukh, S. B., substances rere stripped at a constant Hanamura (65) attempted to improve Zbid., 35, 1867 (1961). current, completion of desorption or the characteristics of a low inertia direct (24) Bouillon, F., Offergeld-Jardinier, >I., reaction being indicated by a potential current motor integrating unit by adding Pison, J., Stevens, J., Schrick, G. van der, Bull. soc. chh. Belyes 68, 153 change. The technique suffers from a tachogenerator correction unit and a (1959). desorption of the substances into the synchronous motor operating \yith the (25) Bourgault, P. L., Conway, B. E., electrolyte and shows rather large direct current motor through a beveled J. Electroanal. Chem. 1, 8 (1959). (26) Boyd, C. M., Menis, O., ASAL. deviations, but it should be useful in gear arrangement to increase effective CHEW33,1016 (1961). some analysrs. output power. hfodification of a direct (27) Braman, R. S., DeFord, D. D., current motor integrator for low cur- Johnston, T. K., Kuhns, L., Ibid., 32, APPARATUS rents and input resistance has been re- 1258 (1960). ported (177). (28) Burke, J., Johnson, L., Division of Use of a direct current Analytical Chemistry, 140th hleeting, Galvanostats and Coulometric motor as an integrator for student ACS, Chicago, Ill., September 1961. Titrators. A constant current source experiments has also been suggested (29) Cassil, C. C., Ibid. using a 24-volt poner supply and (‘71). Hudson and Dickey (80) de- (30) Caton, R. D., Freund, H., Am. Soc. transistor stabilization, capable of scribe a low impedance electronic COU- Testing Materials, Spec. Tech. Publ. lometer composed of a servomechanism No. 272, 207 (1959). producing currents of up to 3 amperes (31) Cekalovic, T. C., Anales .fat. quim. (R13), and a simple transistorized gal- amplifier, an argon lamp relaxation y farm.,liniv. Chile 11,179 (1959). vanostat for student use (121)have been oscillator, and a counter. Although (32)~I Charlot. G.. Jfises au paint chinz. reported. A constant current supply the input impedance of this coulometer anal. pur; et uppl. et anai. bromatol. using a photoresistor as a control ele- is only 15 ohms, its response time is 5,25 (1957). ment, for currents of up to 100 pa. and relatively slow because of the use of a (33) Charlot, G.. Badoz-Lamblina, J., ’ Tremillon,’B., ‘LLes Reactions Eiectro- load resistances of up to 1000 megohms servomechanism-type direct current am- chimiques, Methodes Electrochimique (62),may be useful in nonaqueous solu- plifier, A nonelectronic integrator with D’-Analyse,” Masson, Paris, 1959. tion coulometry. Vorstcnburg and figure registration and a linearity of (34) Clemency, C. V., Hagner, A. F., Loffler (609) suggested that a crystal &0.2yGhas been reported (63). ANAL.CHEM. 33,888 (1961).

62R ANALYTICAL CHEMISTRY (35) Connally, 11. E., Scott, F. A., U. S. (74) Hibbs, L. E., Kilkins, D. H., Anal. (116) Liu, C. H., ASAL. CHEM.33, 1477 Atomic Energy-_ Comm. HW-65919, 28 Chim. Actu 20,344 (1959). (1961). pp. (1960). (75) Hickling, A., Electrochim. Acta 5, (117) hlaekawa, Y., Okazaki, Y., (36) Coulson, D. hI. Division of Analyt- 161 (1961). YakuaakuZasshi 80.1411 (1960). ical Chemistry, 140th Meeting, ACS, (76) Hinton; J. F., Tomlinson, H. M., (118) hiaki, A. H., Giske, D: H., j,Chem. Chicago, Ill., September 1961. -ANAL. CHEM. 33, 1502 (1961). Phys. 30, 1356 (1959). (37) Coulson, D. XI., Cavanauth, L. A., (77) Hoar, T. P., Stockbridge, C. D., (119) Ibid., 33, 825 (1960). ANAL.CHEM. 32,1245 (1960). Electrochim. Acta 3,94 (1960r ’ (120) Pllaki, A. H., Geske, D. H., J. Am. (38) Craig, D. N., Hoffman, J. I., Law, (78) Hobbs, B. B., U. S. Atomic Energy Chem. SOC.83, 1852 (1961). C. A., Hamer, W. J., J. Research Natl. Comm. ORNL-2987, 17 pp. (1960). (121) Mann, C. K., Champeaux, V. C., Bur. Standards 64A, 381 (1960). (79) Holten, C. H., Acta Chem. Scand. J. Chem. Educ. 38, 519 (1961). (39) Davis, D. G.. J. Electroanal. Chem. 15. 9.56 (1961).-, (122) MaSek, J., J. Electroanal. Chem. 1, 1; 73 (1959). ’ (80) ’Hudion, J. B., Dickey, F. E., 416 (1960). (40) Davis, L). G., Talanta 3, 335 (1960). Rev. Sci. Instr. 30, 1020 (1959). (123) hlBth6, I., CsBthy, A., Richter, A,, (41) Delahay, P., Charlot, G., Laitinen, (81) Iinuma, H., Yoshimori, T., Bunseki Acad. rep. populare Romine, Faliala H. -4.,AR’AL. CHEM. 32, KO.6, 103 A Kagaku 9,826 (1960). Cluj, Studii cercetdri chiin. 11, 83 (1960). (1960). (82) Ito, T., Bull. Tokyo Inst. Technol. (124) hlather, W.B., Anson, F. C., As.4~. (42) Desbarres, J., Bull. SOC. chim. France Ser. B. No. 3.159 119601. CHEM.33.132 ,~ (1961). 1961, 502. (83) James, G.’S., Stephen, X. J., Analyst (125) Ibid., p -‘’ ’ (43) Druzhinin, I. G., Kislitsyn, P. S., 85,35 (1960). (126) Mathur , P. B., Anantharainan, P. Trudy Inst. Khim., Akad. Nauk Kirgiz. (84) Jovanovik, hl. S., Kostic, S. Z., N. , Bull. India Sec. Electrochem. SOC.10, S. S. R , So. 6,139 (1955). Glasnik Khem. Drushtm, Beograd 22, 36 (1961).

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Review of Fundamental Developments in Analysis Extraction George H. Morrison, Cornel1 Universify, Ifhaca, N. Y. Henry Freiser, University of Arizona, Tucson, Ark.

ITH the intense emphasis in many of the more sophisticated in- role of extraction in ferrous analysis W recent years on instrumental strumental techniques. (90, 80). An extensive tabulation of methods of analysis, particularly those This review follows the scheme of extractions for the separation of the techniques involving the measurement classification of extraction systems as elements has also been prepared by of physical properties which eliminate set forth by the authors in their book Morrison, Freiser, and Cosgrove (336). or minimize chemical manipulation, it (335) and in their previous reviews (334). Two reviews of interest in organic might be expected that the more The emphasis is on the separation of analysis include one on the determina- classical chemical techniques would be inorganic materials, with particular tion of functional groups (386) and neglected. This is certainly not so in attention to its use in analysis. This another on countercurrent distribution the case of solvent extraction, where review surveys the literature from late methods (166). Irving has written a each year sees a substantial increase in 1959 to late 1961 and follows without chapter on extraction in the Treatise of its application to a large variety of duplication the material presented in Analytical Chemistry (196). Two treat- analytical problems. A review of the the previous review. ments of the subject of liquid-liquid literature reveals the valuable assistance extraction in inorganic chemistry have of this simple separations technique REVIEWS AND BOOKS also been published (98,303). to many fields of analysis, but especially A few general reviews of extraction Of particular importance to radio- in radiochemistry, colorimetry, and for in analytical chemistry have appeared chemistry has been the publication preconcentration in conjunction with (602,640), as well as a discussion of the of a series of monographs on the radio-

64R * ANALYTICAL CHEMISTRY