(3K) Bigeleisen, Jr., J. Cham. Phys. 60, K. G., Muskheleshvili, G. N., Kiladze, i Stabil’n Izotopov i Izluchenii v Nar. 35 (1963). N.Sh., Mikirtumov, V. R., Bakhtadze, Khoz. i Nauke, Moscow (1957). (4K) Boato, G., Casanova, G., Levi, A,, Z. I., At. Energy (U.S.S.R.) 10, 487 (26K) Sakane, R., Isomura, S., Sci.

J. Chem. Phys. 37, 201 (1962). (1961)\----I. Papers Inst. Phys. Chem. Res. (Tokyo) (510 Boato, G., Scholes, G., Vallauri, (15K) Jenn, J. T., Aker, P., Energia 56, 164 (1962). M. E., Nuovo Cimento 14, 735 (1959). Nucl. 5, KO.2, 98 (1963). (27K) Palko, A. .4., Drury, J. S., Bull, (6K) Bulatova, R. F., Grigor’ev, V. N., (16K) Johnson, B. S., F. G., U. S. At. W.E., J.Chem. Phys. 35, 103 (1961). Kogan, V. S., At. Energ. (U.S.S.R.)12, Energy Comm. DP-7S2 (1962),36 pp. (28K) Panchenkov, G. M., Timofeev, 428 (1962). (17K) Katal’nikov, S. G., Andreev, B. M., E. M., Tsimmerman, V. D., U.S.S.R. (7K) Casanova, G., Fieschi, R., Terzi, Xi.. At. Energ. (U.S.S.R.)11, 240(1961). Patent 136.630. Nuovo Cimento 18. 837 ( 1960). (18K) Kauder, L. N., Spindel, W., (29K) Proctdr, J. F., Chem. Eng. Progr. (8K) Clusius K., Schleich, K.; Bernstein, Monse, E. U., J. Phys. Chem. 65, 1435 59, So. 3, 47 (1963). R. B., Helv. Chzm. Acta 45, 252 (1962). (1961). (30K) Simon, H., Heubach, G., Z. Satur- (9K) Clusius, K., Schleich, K., End- (19K) Kenion, A. R., Birch, A. J., Brit. forsch. 18b, So.2, 160 (1963). tinger, F., Bernstein, R., Vogelmand, Patent 896,269. (31K) Stouls, L., Fr. Patent 1,271,501. M., J. Chim. Phys. 60, 66 (1963). (20K) Lazard, B., Belg. Patent 611,155. 132K) Uvarov. 0. V.. Sokolov. N. M.. (10K) Clusius, K., Schleich, K., Pies- 121K) Maimoni. A,. A.I.Ch.E. (Am.Inst. Lvaoin. V. v.. Zhavoronov.‘ X. M.:

bergen, U., Varde, E., J. Chim. Phys. ~ Chem. Engrs. )’J. i,371 (1961j. Zh.‘Vses. Khim. Obschestva hn. D. I: 60, 48 (1963). (22K) Malyusov, V. A,, Orlov, V. Yu., Mendeleeva 7, 695 (1962). (11K) Devyatykh, G. G., Borisov, G. K., Malafeev, N. A,, Umnik, 5. N., Zhav- (33K) Yarshavskii, Ya. M.) Vaisberg, Pavlov, A. A,, Dokl. Akad. Nauk oronkov. X. M., At. Enera. (Cr.S.S.R.) S. E.. Dokl. Akad. Sauk SSSR 140, SSSR 138, 402 (1961). 11, 435 (1961). 1361 (1961). (12K) Gowland, L., Johns, T. F., At. 123K) Merihis. J.. Bousissineres.,, G.. 134Kl Wetzel.,, K.. Isotonen Tech. 1. 15

Energy Res. Estab. (G.Brzt.) Z/R-2629 ~ Anal. Chim. Acta 25,498 (1961). (1660). (1961),12 pp. (24K) Merlivat, L., Botter, R., Sief, G., (3iK) Itolfsberg, M.>J. Chim. Phys. 60, (13K) Grigor’ev, V. N., Ukr. Fiz. Zh. J. Chim. Phys. 60, (1963). 15 (1963). 6, 472 (1961). (25K) Muehlenpfordt, J., Siewert, G., (36K) Zel’venskii, Ya. D., Efremov, A. (14K) Gverdtsiteli, I. G., Nikolaev, Yu. Gagua, T., Tr. Vses. Nauchn.-Tekhn. A,, Itv. Vysshikh Gchebn. Zavedenii, V., Oziashvili, E. D., Gverdtsiteli, Konj. PO Primeneniyu Radioaktiun. Khim. i Khini. Tekhnol. 5, 727 (1962).

Electroanalysis and Coulometric Analysis Allen 1. Bard, Department of Chemistry, The University of Texas, Austin 12, Texas

HIS PAPER surveys the literature tails about the experimental conditions, concerned with the effect of surface Tand developments during 1962 and is included. ii book on coulometric oxidation, activation, and adsorption through December 1963, although methods by Abresch and Claassen (5) on the rates of electrode reactions. papers published before 1962 which has also appeared. Oxide Films and Surface Effects. have not appeared in previous reviews An extensive review on the analytical The nature of the surface films on in this series have also been included. applications of mercury electrodes to solid electrodes continues to enjoy electrodepositions, separations, and attention. The mechanism of the formation and reduction of the oxide BOOKS AND REVIEW ARTICLES coulometric methods has appeared (208). This review contains tables film on platinum was discussed by Several books dealing wholly or partly listing the elements determined and Feldberg, Enke, and Bricker (76). The with electroanalytical methods have separated on mercury electrodes and authors used various cyclic techniques appeared. A welcome English trans- the experimental conditions employed to study oxide film effects and con- lation of the book by Charlot, Badoa- in the methods. The literature between cluded that the formation occurs in Lambling, and Tremillon (46) has been 1948 and 1960 is surveyed, and 423 ref- two, one-electron, steps, involving the published. The book is written mainly erences are given. Application of slow formation of Pt(OH),, followed by for analytical chemists and uses current- electrolytic methods to trace analysis a rapid step yielding Pt(O),. On reduc- potential curves and graphical methods has also been reviewed (137, 169). X tion, the reverse steps occur; reduction to treat a variety of electroanalytical general review of electroanalytical of Pt(O), to Pt(OH), is rapid, and of techniques. Xumerous applications are methods appeared in the annual report Pt(OH), to platinum is slow. The given and the book is highly recom- of the Chemical Society (London), (44). mechanism of surface oxidation of mended as an introduction to this field A number of review articles on coulo- platinum has also recently been dis- for the practicing analyst. Volume 4 of metric methods have appeared. Of cussed by Gilman (89). Part I of the treatise by Kolthoff and special interest to English-speaking, Evidence for a series of platinum ox- Elving (121) is largely devoted to elec- chemists is the review by Kies (115), ides on the electrode surface has been trical methods of analysis. Chapters on with 267 references, on coulometry. presented (133, 168). Mayell and the fundamentals of electrode processes, A brief review of applications of con- Langer (168), by oxidizing platinum electrodeposition, and coulometric trolled potential coulometry to metal potentiostatically or with a constant cur- analysiq are included. Kechnitz’s mono- analysis has appeared (65) as well as rent in acidic solutions, removing any graph, “Controlled Potential Analysis,” other, foreign language, reviews on gaseous oxygen and electrolytically re- (209)has just appeared and is a valuable coulometric methods (1, 2, 178, 250, ducing the surface oxides, showed that addition to the literature of electro 234, 244, 301). the number of coulombs involved in the analytical chemistry. The theory and reduction of the surface depended upon a1)j)aratus of both electrogravimetric ELECTROCHEMICAL THEORY the potential to which the electrode was and coulometrir controlled potential oxidized. Increasing the potential of method. are divuased extensively, and Many of the fundamental electro- preoxidation increased the extent of oxy- an clement-by-element survey of ap- chemical studies most directly ap- gen coverage up to a potential of about plications. in most cases including de- plicable to electroanalysis have been 1.8 volts us. N.H.E. Above this poten-

70 R ANALYTICAL CHEMISTRY tial the number of coulombs decreased to responsible for an increase in reversibil- H&O, and washed) and passive (heated a constant value. The authors propose ity of the electrode reaction (18). in oxygen at 850”, forming a stable a series of platinurn-oxygen couples, Evidence that a fresh layer of finely oxide coating) electrodes and found ending with a “tighi,” platinum oxide divided platinum increases the rate of that the rate of reduction at an active at potentials higher than 1.8 volts. an electrode reaction has been obtained electrode was about double that at a Kozawa (133) found !lumps on current’- in other studies. Shibata (237) passive one. These authors also found potential scans for a platinum electrode examined the effect of preoxidation and that hydrogen oxidation occurs at in strongly alkaline solutions and as- reduction of the electrode on the over- active electrodes but not at passive ones. cribed these to various platinum oxide potential for hydrogen ion reduction These results are in disagreement with and hydroxide couples. and concluded that the beneficial effect those of Sawyer and Seo (228) who Some previous experiments on of this anodization-cathodization pro- found no evidence for hydrogen oxida- platinum oxide formation have been cedure is not due to impurity desorption, tion at gold electrodes. The reduction repeated and reinterpreted. Previous hut, rather to “a freshly electrodeposited of oxygen at palladium electrodes was results indicating preferential oxide platinum. . . layer which has high studied by Blackburn and Lingane (32). formation at grain boundaries have been activity associated with a small crys- The behavior here was similar to that questioned (181). Breiter (38) has re- tallization rate.” Similar evidence found for the reduction of oxygen at examined the chemic:tl stripping of sur- for active centers on a platinized gold electrodeq. Evidence for two face oxides in chloride media and con- elec7trode has been presented (SI,190). palladium oxides at the electrode sur- cluded that the stririping of the oxide The electroreduction of oxygen at face was presented. occurs by an electrocl- emical mechanism platinum has been investigated further Adsorption Effects. The adsorp- rather than by a direct chemical re- (180, 627) and additional evidence is tion of various components from the action, and that the experiment does not presented for the reduction of oxygen solution, including the electroactive demonstrate a true oxide film as opposed with less overpotential at a freshly species itself or the products of the t,o chemisorbed oxygen. Peters and oxidized electrode. electrode reaction, can also afiect the Lingane (203) examined film formation The oxidation and reduction of H202 rate of electrode reactions. Well in chloride media at several pH’s and at a platinum electrode have been known methods, such as electrocapil- concluded that platinum chloride and studied (146) and both reactions directly larity measurements and analysis of oxychloride films containing both plat- involve participation of the electrode polarographic pre- and postwaves have inum(I1) and platinum(1V) form. surface. The H,02 also undergoes a been used for some time to study ad- Work continues to accumulate on the catalytic decomposition at the platinized sorption at mercury electrodes. Some effect of surface oxides on the rates of electrode (146) [and also at iridium and recent work on the measurement and electrode reactions. General evidence palladium electrodes (SI)]. The oxida- effect of adsorption on solid electrodes appears to support t”ie conclusion that tion of hydrogen at platinum electrodes is reviewed. For a review of previous oxide films hinder most electrode re- was studied by Sawyer and Seo (228) work on adsorption at solid electrodes actions, both oxidaticns and reductions, and was shown to involve reduction of and its effect on electrode reactions, es- and that an electrode can be activat,ed the oxide film and platinization of the pecially on the hydrogen-hydrogen by forming a film of finely divided surface. Breiter (37) has indicated that ion system, the recent chapter by metal on its surface by oxidation of the the reaction between the oxide film and Frumkin (83) should be consulted. electrode followed by reduction. hydrogen occurs by an electrochemical The extent of adsorption of a species Kabanova (111) showed that the mechanism. It has also been shown from solution on an electrode can be oxidation of iron(I1) occurs less re- that formation of oxide on the active measured using radioactive tracer versibly on an oxidized platinum centers of a platinum surface inhibits methods, involving such isotopes as electrode. In general, t’he overpotential the hydrogen oxidation reaction (4, 36). carbon-14 and sulfur-35 (57, 58, 91, for ferrous ion oxidat,ion at a rotating Surface oxide effects on other metals 297) and ultraviolet spectrophotometric disk electrode increased by up to 200 have also been observed, and generally techniques (26). Adsorption of elertro- mv., depending upon the duration of these effects parallel the behavior found active species and products has been oxidation of its surface and the with platinum. Kabanova (110) found studied using chronopotentiometric (16, magnitude of the potential at which the that the rate of oxidation of ferrocyanide 101, 199) and linear scan voltammetric oxide film is formed. at a rotating gold electrode is decreased (87, 88, 200) techniques. Evidence for Anson and King (!I) similarly dem- by an order of magnitude by oxidation adsorption of substances which interfere onstrated that thl. increased re- of the electrode. The reduction of with electrode reactions by blocking of versibility of reduction of iodate and oxygen at gold electrodes was studied active sites, preventing adsorption of vanadium(V) previously ascribed to the by Evans and 1,ingane (74). The the electroactive substance, or pro- presence of a thin oxide layer, is caused course of the reaction was found to moting recrystallization of the c>lectrode by activation of the electrode by a layer be very dependent upon the electrode surface, has been presented. .inson of finely divided pla1;inum. Oxidation pretreatment and the nature of the and Schultz (12) showed that adsorp- of the elect’rode surface was also shown electrode surface. .4t an electrode which tion of chloride and thiocyanate ions to hinder t8he reductim of peroxydisul- wap recently oxidized and reduced, and amyl alcohol inhibited the adsorp- fate ion (160) and the oxidation of reduction of oxygen in an alkaline tion and subsequent oxidation of oxalic hydroxylamine (60) at a platinum medium occurred in essentially a single acid at a platinum electrode. Bala- electrode. wave, corresponding to reduction first to schova (14) studied the effect of Similarly ax. impedance measure- H,On (or HOZ-) followed by catalytic electrode pretreatment on the extent ments demonstrated that both the decomposition of the peroxide at the and kinetics of adsorption of ions, and chloride-chlorine (,‘61) and the active electrode surface. At an aged demonstrated that adsorbed ions can bromide-bromine (150) systems are electrode, where the catalytic decom- retard oxygen adsorption (or oxide film made less reversible hy the oxidation of position occurs more slowly, two waves, formation). This retardation of oxide the electrode. The oxidation of hydra- corresponding to the reduction of film formation can have the effect of zine was first reported to be made more oxjgen and the intermediate H202, increasing the rate of an electrode reversible by oxide filtn forrnation (112), occur. reaction. For example, addition of but later work indicated that here too a Flozental and Veselovskii (218) also bromide ion increases the ease of oxida- freshly formed layer of finely divided studied the reduction of oxygen at tion of the cobalt(I1)-EDTA (10). Part platinum, rather than the oxide, was active (treated with hot concentrated of this effect is ascribed to pre-

VOL. 36, NO 5, APRIL 1964 71 R vention of formation of the oxide film by increasing the rate of mass transfer of diaminocyclohexanetetraacetic acid preferential adsorption of bromide ion, the metal ions to the electrode. Of (I@),are given. although electron bridging by bromide course the selectivity of an electrolysis carried out under these conditions is not ion or prevention of adsorption of the ELECTROGRAVIMETRY electroactive species itself may also be so high as that of a controlled potential involved. separation using vigorous applied Beronius (28) has presented an In many cases, however, adsorption of stirring. electrodeposition method involving nonelectroactive substances hinders the Electrolytic separations in radio- radioactive tracers for measuring the electrode reaction (or "poisons" the elec- chemical procedures continue to be used. rates of moderately rapid exchange trode). Iodide ion has been shown to re- Millard (172) described the separation reactions. For example, to measure the tard the reduction of oxygen at platinum of lead-212 and polonium-210. Electro- rate of the exchange reaction electrodes in acidic or neutral media separation before neutron activation (%IS),inhibit the oxidation of hydrazine analysis was described by Lux (152). CH3I + I*- = CHd* + I- (It?), and cause the reduction of iodate During the determination of traces of ion to occur less reversibly (11). Simi- Ag in a mixture containing Cd, the first only radioactive iodide (I*-) is larly adsorption of sulfide ion decreases reaction Cd1Io(n, p)Ag"O forms silver added to a cell. (The asterisk denotes the reversibility of the bromine-bromide and causes interference. Silver was radioactivity.) Iodide is deposited for ion couple (150). Klyanina and Shlygin separated from up to lo8 times more Cd a known time (about 300 seconds) at a (120) investigated the effect of Hg, As, by electrolysis at a rotating cathode with silver anode, and the activity of the and CK- on the electroreduction of a 99% yield. Samartseva (224) de- electrode is noted. Then CH31 is added SO2 at a platinum electrode. Only scribed the separation of americium- and iodide is again deposited, pre- cyanide was found to inhibit the 241 and curium-242 from "03 solu- sumably under identical electrolysis electrode reaction, and formation of tions adjusted to a pH of about 3 at a conditions, for the same time, and the platinum cyanides at the electrode sur- platinum cathode (probably as hydrous activity is measured again. Since some face was suggested Adsorption effects oxides). Molnar (186) has devised a of the I*- is now exchanged, the activity have also been observed during the glass column packed with rings of measured the second time will be lower, oxidation of hydrogen at a platinum platinum wire acting as a cathode for and from this change in activity, the electrode (4, 83) and for the reduction continuous electrolytic separation of rate of the reaction can be determined. of aromatic nitro compounds (105). carrier-free radioisotopes. Controlled Potential Methods. These studies have various applica- Electrolytic separation of the Electrodeposition of metals in the tions to electroanalytical methods. lanthanideelements also continues (107). presence of EDTh continues to be of Solid electrode pretreatment procedures Use of amalgam cathodes and a interest and methods for the con- generally involving repeated oxidation methanolic medium containing LiCl trolled potential electrodeposition of and reduction of the electrode surface has been reviewed, and the separation Ag, Cu, and Hg have been developed will often prove beneficial. Similarly of small amounts of Tm in Lu studied (84, 284). Tanka continued his studies elimination of adsorbable ions and sub- (197). Studies of Lu and Ho enrich- of the controlled potential deposition of stances may be necessary in some cases. ment in boiling methanol have also a number of metals in various media. Harrar (95),for example, noted that a been made (196). Separation of Pm The deposition of hg, Hg, Au, Bi, Cu, rigorous pretreatment procedure was and Sm from other elements in the Pb, Te. Se, Pd, Cd, Co, Fe, Ni, and Zn necessary for the successful coulometric group at a mercury cathode has been in pyrophosphate media of pH 7 and 10 determination of H202 at a platinum described (143). (273), alkaline triethanolamine media electrode. Addition of halide ions in Kovalenko described a series of (274), formic acid-formate buffer at this case also appeared to have a re- electrolytic separations of metals, in- pH 4.1 (216),and an acetic acid-acetate tarding effect on the electrolysis. Pref- cluding separation of Bi from Cd, using buffer at pH 5.3 (276) was investigated. erential surface effects may be useful in an amalgamated copper electrode (128); Potentials and electrolysis conditions certain cases. For example, the pres- Pb from Cd, as PbOz (150) and on an for the deposition of the metals at a ence of a film of tin hydrous oxide on a aluminum cathode (124); Bi from Si platinum cathode are given and many platinum electrode, formed by cathodiz- (125); Cu from Ti (126); Cu and Bi successful determinations are de- ing the electrode in a solution containing from Zn (127); and Bi from several scribed. tin(IV), has been found to increase the metals (129). Tsyb and Sayun have Alfonsi (6) described procedures for the hydrogen overpotential at the electrode studied the separation of In from Zn electrodeposition of Sb, Pb, Cu, and Sn and allow the generation of stannous ion and Fe (255) and from Cu (286) by in lead- or tin-baqed alloys, and of Bi, at close to 100% current efficiency for electrolysis at a mercurycathode. Other Pb, Sb, and Sn, in bismuth-based coulometric titrations (19). separations reported include the separa- alloys. Lanese and .Jaselskis (140) tion of vanadium compounds in aqueous determined Te by electrodeposition at solutions (90); the separation of p- a copper cathode from a supporting ELECTROSEPARATIONS titanium (304); and the separation of electrolyte consisting of zLbf HLSOI, Herringshaw and Kassir (102) studied hydrogen in steel by a previously 0.4M (KH&S04, 0.1M sodium tartrate, the effect of electrode area, current reviewed method (119). and 0.06X NaN03 at a potential of density, and applied stirring on the rate Internal electrolytic procedures have -0.6 volts us. a saturated mercurous of electrolysis at a mercury electrode. been applied by Lipchinski and co- sulfate electrode and showed that They found that the rate of deposition horkers to the separation and deter- the average error was less than 1%. of Cu, Cd, Zn, and Fe from 0.3iV &So4 mination of several substances. In all A statistical study of the controlled is higher under constant current con- cases the electrolytic procedures em- potential deposition of Cu from various dition< v hen the applied current is ployed platinum anodes and PbO? aqueous solutions has been made (300), greater than the limiting current for cathodes and m-ere used to adjust the and the authors conclude that the deposition of the metal, than under oxidation state of the element, which method is most precise and accurate controlled potential conditions. The was then determined by a photometric from a HXO3or tartaric acid supporting higher rate under constant current method. Procedures for the oxidation electrolyte. conditions is ascribed to the simul- of chromium(II1) to chromate (147'1, Controlled Current Methods. Tan- taneoui rapid evolution of hydrogen arsenic to the V state (149, and man- talum and platinum-clad tantalum gas at the electrode surface, effective in ganese to the 111 state in the presence of electrodes have been used successfully

72 R ANALYTICAL CHEMISTRY for the electrodeposition of Cu and the current is halved and the electrolysis medium. The coulometric determina- Ag (194). The determination of Cu in continued; the current is halved each tion of Hg at a mercury-plated platinum high manganese brassems was found to be time the electrode potential reaches the electrode has been described (7). successful when organic reducing agents, limit. As originally designed, with a Harrar and Stephens (96) determined such as methanol or formaldehyde, single constant current, the technique hu by reduction of gold(II1) at a gold- were added to the electrolysis medium had the advantage of not requiring a plated platinum electrode in an HC1 (47). h procedure for determining Xi coulometer. In the present case, how- medium. The background eorrection and Mo has been described (208). The ever, a fairly complex device which was very low in this determination and deposition of Re at ti platinum gauze halves a timing pulse frequency counted errors of less than 0.1% were obtained cathode from a 2N I&S04 solution at by an electronic scaler is needed. Since for milligram amounts of Ah. 70" yielded results wii;hin 1% for 10 to the electrolysis must take longer by this Reduction of iron(II1) to the I1 state 30 mg. amounts of Re (233). technique than by conventional con- and its subsequent re-oxidation formed Internal Electrolysis. Deschamps trolled potential coulometry, and the the basis of a determination by Milner and Bonnaire (66) have investigated apparatus is no simpler, it is hard to see and Edwards (175). The coulometric the application of various anodes to the the advantage of this technique. The determination of Fe based on the deposition and determination of Au, Bi, determination of Cd, Cu, and U in a internal electrolytic oxidation of iron(I1) and Sh at a platinurn cathode. Pro- citrate medium with errors of about has also been described (235, 236). cedures based upon the use of a Pb, Zn, 0.3% was described. Controlled pot'ential coulometric re- or Mn anode and various anolyte and Bard (17) devised an apparatus con- duction of dichromate at a gold electrode catholyte compositior:s are given and sisting of a fast potentiostat and coulom- has been used for the preparation of a metals in 1 to 3 m,;. amounts were eter and a cell using a larger electrode standard chromium(II1) solution (98). determined to within a few per cent. area-solution volume ratio and ultrasonic The determination of milligram amounts Ahinternal electrolytic procedure for stirring, and showed that electrolysis of In, by reduction of indium(II1) at a the determination of Se by precipitation times of the order of one to two minutes mercury cathode and by re-oxidation of of CuzSe was found useful for deter- could be obtained under these con- the indium amalgam in a chloride mining about 5 mg. of Se with an ditions. The application of this appa- medium, with errors of !ess than 0.2%, nbsolute error of about 0.3% (282). ratus to electrode mechanism studies has been described (IG??) Shiobara (238) described an internal was also described. Van Norman (289) A previously reviewed method for the electrolytic method for the determina- demonstrated that the technique of con- determination of T1 by reduction at a tion of Ag, Cu, and Zn. Methods for trolled potential coulometry could be mercury electrode has been tested the determination of Cu, Zn, T1, and successfully applied to analysis in (195). Dunlap and Shults (70) deter- Mn have also been reviewed (302). fused salt media. Determinations of mined Sb in both the 111 and V state by An analysis of ores for Bi based on an Zn, Cd, Ni, and U in a LiC1-KC1 reduction at a mercury electrode in a internal electrolytic procedure has been eutectic at 450" are described. Be- tartrate medium. The reduction of described (219). Facsko and Radoi cause of a considerable cathodic back- pertechnetate ion was shown to occur (75) discussed interna. electrolysis with ground current, the most accurate pro- stepwise, yielding two closely occurring vibrating electrodes, and demonstrated cedure involved plating the metals and waves of three and one electron each, in the utility of their method in the then coulometrically stripping them. HZS04 and chloride (222) and tripoly- determinat,ion of Cu. During the past two years the atomic phosphate (278) media. Although cou- weight table was changed to one based lometric reduction to technetium( I1 I) CONTROLLED POTENTIAL COULOMETRY on carbon-12 as a reference so that the at a mercury electrode was possible in new value for the faraday is 96,487.2 all media, the errors were somewhat Some new techniques involving con- coulombs per equivalent. lower in the tripolyphosphate medium. trolled potential coulometric deter- Metals. Application of this tech- Cokal and Wise (50) described the minations have been described. nique to the determination of the determination of Na in an acetonitrile Hanamura (94) continued his study of actinide elements continues (174). medium. Sodium(1) was reduced at a the I-Q recorder. In this recorder the Methods for the determination of U,in- mercury electrode at -2.3 volts 21s. synchronous motor ordinarily used to cluding the use of a hg cathode (177) SCE and re-oxidized at -0.10 volt, drive the X- or time-axis is replaced by and solvent extraction procedures be- with an error of less than 2% for 1.31 Hanamura's integrati ig motor, a low fore electrolysis (33, 242, %'@), deter- pmoles of Ka. The application of inertia direct current motor equipped mination of mixtures of U in different nonaqueous solvents to other similar with a tachogenerator correction unit oxidation states in a tripolyphosphate determinations seems promising. and a beveled gear differential to in- medium (305) and in the presence of Segatto (232) determined Ph, Cd, and crease the output power, so that the nitrate ion (240), as well as other Zn in glasses at the milligram level. X-axis is now a function of Q, the total techniques (287) have been described. Coulometric precipitation analysis of coulombs passed during the electrolysis. Methods for the determination of I'u metals has been mentioned in a Russian Since Q is directly proportional to I, the (64,176, 239, 241) and Kp (85, 174) patent (288). electrolysis current, during the usual have also been published. Other Determinations. The de- constant potential determination, a The reduction of iridiunilIV) has termination of H20z (95) has already linear plot is obtainell on the I-Q re- been studied. Page (201) showed that been mentioned as an examplc of a corder, and the initial linear portion can the one-electron reduction could be determination in which the electrode be extrapolated to find the final Q. accomplished successfully in an HCl reaction is dependent upon the surface This technique was wccessfully used medium. Rechnitz and McClure (211) state of the electrode. It is interesting for the determination of Cu, Pb, and Cd showed that the indications of a reduc- that although t'his reaction is pertiirhed in mixtures with an error of about 2% tion of iridium(JV) involving more than by oxide film and adsorption eflects and at the 10 pg. level. one electron in a HCIOp medium nere the catalytic decomposition of H20?at A technique called constant current caused by the secondary reaction of the electrode surfarr, by using 1)roI)er potential limit coulometry has been iridium(II1) and perchlorate ion, re- pretreatment procedures and high speed devised (153). This txhnique is based generating iridium(1V). Rechnitz(210) , Harrar was able to deter- on the application of a constant cur- also showed that rutheniumiIV) could mine milligram amounts of H20Zwith rent to a cell until the electrode potential he reduced coulometrically to the I11 relative errors of less than 0.29;. he- reaches a preset limit, at which point state at a mercury cathode in a chloride treatment of the elertrode aah also

VOL. 36, NO 5, APRIL 1964 8 73 R necessary in the determination of quired in the overall reaction. Dapo metric experiment, was shown to agree hydrazine by oxidation at a platinum and Mann (59) observed that the with that determined by spectrophotom- electrode (35). The mechanism of this coulometric oxidation of triethylamine etry and polarography. Another type reaction has been studied (18, 122) and in dimethylsulfoxide involved transfer of complication occurring during coulo- secondary electrode reactions, surface of one electron followed by a rapid metric determinations is the induced re- oxidation and adsorption effects, and chemical reaction. The coulometric re- action, the reduction (or oxidation) of catalytic decomposition of hydrazine duction of pyrimidine and related com- the solvent or supporting electrolyte were shown to occur (see below). In pounds in aqueous buffers was studied induced by the simultaneous reduction 1.W HzS04, 55 to 440 pg. of hydrazine by Smith and Elving (245). (or oxidation) of the electroactive sub- were determined with a relative error While many of the previous studies stance being determined. Evidence for of about 0.5% (36). showed an integral number of electrons an induced reaction was found during The determination of thiourea by gained or lost in the overall reaction the electroreduction of manganese(I1) oxidation at a platinum electrode has scheme, many coulometric studies, es- (186) and also during the reduction of been described (226), as well as the pecially those involving organic dimethylglyoxime (248). coulogravimetric procedure for the de- electrode reactions, show apparent elec- Ficker and Meites (78) examined the termination of mixtures of chloride and tron changes, naPp,which are variable coulometric reduction of zinc(I1) at a thiocyanate ions (158). Yamada and and nonintegral. Recent studies have mercury electrode and its subsequent Sakai (299) determined cyanamide by been concerned with treating these types stripping, and noted that not all of the precipitation of the silver salt, with of coulometric determinations theo- zinc was recovered when the plating subsequent dissolution in HN03 and retically, and using the variation of was carried out in the presence of cer- coulometric determinatioh of silver. napp with experimental conditions to tain other metals, such as Co. This was Langer and Landi (141) devised a tech- help elucidate the overall reaction ascribed to the occurrence of inter- nique called electrogenerative hydrogen- mechanism. Bard and Mayell (20) metallic compound formation-e.g. , ation, which could be applied as an in- theoretically treated cases where an Zn-Co-Hg-a phenomena well known in ternal electrolytic coulometric tech- intermediate formed in the electrode re- stripping voltammetry at a hanging nique. The anode is the usual hydrogen action underwent first or second order mercury drop electrode, and the current- fuel cell anode and hydrogenation of chemical reactions and then R sub- time curves during the stripping were olefins occurs at the cathode. Applica- sequent electrode reaction A very sim- used to study the rates of the stripping tion of this technique to the determina- ilar case for a second order intervening reactions and the species involved. tion of olefins with no more apparatus chemical reaction was also treated by The existence of complicating than a low resistance coulometer appears Meites (170). Bard and Solon (23) chemical reactions must be considered promising. treated reactions in which the electro- when devising coulometric anaylsis of Electrode Mechanisms. The use active species was produced by a slow both organic and inorganic substances. of coulometric methods in the study chemical reaction or underwent a simul- Sometimes strictly mathematical cor- of the rates and mechanisms of elec- taneous chemical reaction and electrode rections can be made for the com- trode reactions has been extended. reaction. Considering the variation of plicating reactions, after these re- The determination of the number of naPp and the current-time behavior actions have been studied in detail electrons involved in electrode reac- during the electrolysis, criteria were (186),although often this procedure will tions is well known, and many previ- established for identifying the type be sufficiently complicated as to dis- ous studies of metal ion reductions of complication occurring during the courage its use in practical analysis. and oxidations of organic substances electrolysis. Csing this technique, Often a change in the solvent, sup- have been made. A sampling of some Mayell and Bard (167) studied the porting electrolyte, or temperature will recent applications to the determina- electroreduction of quaternary ammo- decrease the effect of the complicating tion of the number of electrons in- nium compounds. reaction (112, 167). Higher rates of volved in reactions include the follow- Karp and Meites (112) studied the electrolysis will also minimize the effects ing. Wilson, Butler, Ingle, and Taylor oxidation of hydrazine at a platinum of intervening chemical reactions (1 7). (295) found that the aminoacridines electrode and observed that naPpde- creased from the expected 4.00 (for were reduced at a mercury cathode via CONTROLLED CURRENT a one-electron reduction, except for the complete oxidation to NJ as the hgdra- COULOMETRY-COULOMETRIC TITRATIONS 5-aminoacridine, whose reduction ap- zine concentration was increased and parently involved a direct two-electron the hydrogen ion concentration de- Determinations. A summary of transfer. Butler and Martin (43) re- creased. h mechanism for this varia- determinations using electrogenerated ported that crystal violet reduced in a tion, based on an intervening coupling titrants is given in Table I; some one-electron reaction, but that the reaction of the product of the first specific considerations are discussed reduction of another triphenylmethane electrode reaction, was proposed by below. Marinenko and Taylor (168, dye, brilliant green, was more complex. them, and was shown to be consistent 159) continued studies into the pre- The perylene cation radical was re- with this type of mechanism (20). cision of coulometric titrations. Potas- duced in a trifluoracetic acid medium The complication during the electro- sium dichromate in half-gram samples, to perylene by a one-electron reaction at reduction of tropolone, as studied by was titrated with electrogenerated iron a mercury electrode (272). Tanaka and coworkers (277), probably (11) with a standard deviation of 0.003% Hoffman (104) found that alloxan is also involves a cheirtiral reaction inter- (169). ,4 discussion of the current reduced irreversibly at a mercury vening between two electrode reactions. efficiency of iron(I1) generation based electrode in neutral media via a one- Moros and Meites (186) also found a on current-potential curves was also electron reaction. Eriochrome violet B second order intervening chemical re- given. By use of similar techniques, underwent a four-electron reduction in action during the electroreduction of four milliequivalent amounts of the aqueous solutions of pH 4.6 to 11.2 manqanese(I1) in a cyanide medium. halides were titrated with eleotro- (79). Masui and Say0 (162) studied the This reaction involved the reaction of generated silver ion with a standard coulometeric reduction of 2,2-dinitro- a manganese(1) species with HCN, deviation of 0.005% (158). propane in various ethanolic buffers. regenerating manganese(I1) and A differential coulometric technique In alkaline solutions a two-electron yielding n,,,-values larger than ex- for improving the accuracy and pre- reduction was found, while in acidic pected. The rate constant for this re- cision of coulometric titrations has been solution four electrons per mole were re- action, measured during the coulo- described by Monk and Goode (183).

74 R rn ANALYTICAL CHEMISTRY Two coulometric titration cells are con- nected in series, one containing a Table I. Electrogenerated Titrants and Substances Determined By Coulometric standard amount of the substance to be Titration determined and the lither, the sample Electro- Electro- with slightly more of the constituent of generated Substance Refer- generated Substance Refer- interest. The titration is carried out at titrant determined ence titrant determined ence a high uncontrolled current until the Oxidants Cerium(IV) Hydroxylamine (620, 269) end point in the standard cell is ap- Hydrogen (220,269) Chlorine Hydrazine (108) peroxide proached. Then a small known con- Cyclic p- (92, 291 ) Ferricyanide Selenious acid (188) stant current is used to determine the diketones Bromine Thallium(1) (81) excess of the constituent in the sample Reductants cell. Dichromate sariples of about 32 Aluminum (via (122) S-hydroxy- Iron(I1) Vanadium (179) mg. were determined by titration with quinolate ) Permanganate (271) electrogenerated iron(IT) with error of Zinc(II), copper ($9) Chlorine (71, 262, about 0.005y0 using this technique. (11) (as thio- 271 \ .A study of the current efficiency for cyanates Dichromate (169,-h71) so2 (266) Tin(I1) Cerium(IV), (221,268) the generation of chromium(I1) at a Hexamethylditin (260) iodine, bromine mercury electrode m,s made by Bard Cyclic p- (92, 291 ) Iodine (254) and Petropoulos ($I), and a supporting diketones Chromium Copper(I1) ($1) Methyl vinyl (306) (11) electrolyte composed of 0.1121 chromic ketone sulfate and 0.lM potassium chloride Uranium(V) Iron(II1) (15) Quinine (258) Titanium p-Quinone (68) was found most suitable. Some studies Ascorbic acid (113) (111) dioxime of coulometric titrations with electro- Olefins (6,27, 161 Vanadium, iron (55) generated tin(I1) ha1 e appeared (621, 173, Biphenyl Reducible (157) 21L. radical organic 268) recommending a chloride sup- 29i j anion subst an ces porting electrolyte ,tnd a platinum Hydrazine (208) generating cathode. Under these con- Carboxylic acid (135) hvdrazides Precipitating and Complexing Agents ditions, however, a current efficiency of Ammatic amines (63) Silver(1) Chioride, chlo-, ($52) only 94 to 96% can be obtained, and N,N'-diphenyl- (154) rine in organic even this depends upon some special p henylenedi- compounds surface effects at a pla inum electrode in amine Halides (158,263) these media (19) ; the previously re- Phenols (62, 131) Potassium (via (261) Iodine Hydrazine (108) the tetra- viewed methods of generating stannous Hexaethylplum- (259) phenylborate) ion, based up on a bromide supporting bane Orthophosphate (48) electrolyte and a gold cathode, seem Ascorbic acid (113) Thioglycolic Organomer- (171 ) preferable. Hypobro- Ammonia (49, 136) acid curials mite EDTA Ca++ Ni++, (184) Buck and Crowe :41) made a de- Aminoxy group (134) cu;+ Zn++ tailed study of the current efficiency of Iron(II), anti- (123) Sr++'Cd++' the electrogeneration of manganese(II1) mony( 111), Ba+$,y+++ Pb+:ce++'+ and iron(I1) at platinum, carbon, and Niohium-~ ...-... tin(I1) ($50) ce++l-+, J boron carbide electrcdes. Buck (40) Manganese Oxalic Acid (256) Nd+++ also studied the application of various (111)- Thorium ( 283 1 end-point detection twhniques in con- Iron(11) Ferro- Copper( 11) ( $64 ) nection with these titrants. Laitinen system cyanide and Liu (139) recently studied the current efficiency for ;plating and strip- ping chloride ion at a silver electrode at various current densities and chloride cessful. The method should prove use- matic acids in an isopropanol-water ion concentrations. At high chloride ful for other radicals and solvent systems, medium. Pyridine was successfully ion concentrations and low current and may also yield information on the determined in an aqueous medium using densities formation of AgCl2- occurs, thermodynamic properties of free a photometric end point (1PQ). The while at low chloride ion concentrations radicals. use of anion and cation exchange and an applied current density greater Macero and Janeiro (154) used membranes for separating the anode than the limiting cui rent for chloride electrogenerated bromine in a glacial and cathode compartments in acid-base deposition, the current efficiency also fell acetic acid medium to form the radical titrations was investigated (106). below 100~O.Optimum conditions ap- of X,N'-diphenylphenylenediamine, and Fairly large errors were obtained in peared to be at a 0.01N chloride ion demonstrated that the electrode re- titrations of acids, but the titrations concentration and a current density action involved one equivalent per mole with electrogenerated hydrogen ion range of 5.5 to 4100 u&. per sq. cm. of electroactive substance. By using an were more successful. A detailed dis- Maricle (157) has introduced the new ethanol medium, Christian, Knoblock, cussion of the theoretical and experi- and potentially important technique of and Purdy (48) were able to titrate mental current-potential curves with using electrogeneratecl free radicals in orthophosphate by precipitation of the platinized and polished platinum elec- aprotic solvents as coulometric titrants. fairly soluble silver salt. Extension of trodes has been given (51),and applica- The generation of biphenyl radical the use of nonaqueous solvents for tion of those electrodes to coulometric anion in dimethylforinaniide solutions oxidation-reduction and precipitation acid-base titrations has been discussed. containing 0.1M biphenyl and 0.1M titrations will probably prove to be a Methods for determining carbon and tetra-n-butylammonium bromide at a fruitful field for research. hydrogen in steel based on the coulo- platinum cathode was described. Water Interest in acid-base titrations in metric titrat'ion of C02 by Ra10H)2 did not constitute a se-ious interference, nonaqueous media and investigations of generated coulometrically from 13aC12 and the titrations ol' several organic end-point detection methods for these have been reported. In the determina- compounds, including mthracene, nitro- continue to hold interest. Suzuki tion of carbon (99), oxidation to GOn methane, and benzop ienone, were suc- (255') considered the titration of aro- is direct. For the hydrogen deter-

VOL. 36, NO. 5, APRIL 1964 * 75 R mination (86),the evolved H2is oxidized gane (73, 145) used coulometric oxida- APPARATUS with CuO to water, which is reduced tion of a gold anode in halide media to with graphite at 1200" C. to H2 and study equilibria involving gold( I) and Lewin (144) has discussed the funda- CO. The CO is finally oxidized to COS gold(II1) in chloride and bromide mentals of electroanalysis instrumen- by passing through a tube containing media. Further applications of coulo- tation. -1 cell useful for coulometric silica gelJ Na2COs, and Mg(C104)2and metric titration procedures for the and other electrochemical studies of determined as described. Ai method determination of C1- and S-containing small quantities of gas has been devised based on the direct coulometric deter- effluents in gas chromatography have (281). Kesler (114) described an mination of the water itself (see below) been made (45, 67, 279). electrolysis cell for constant current seems more straightforward. Continuous Coulometric Titrations. generation of titrants for use in con- Determination of water by coulo- Takahashi, Siki, and Sakurai (266, 267) tinuous analyzers. metric methods continues to find new reviewed the fundamentals and working Coulometric Titration Apparatus. applications. Karl Fischer methods, methods for automatic continuous Several general automatic coulometric with various modifications, continue to coulometric titrations. Some applica- titrators have been described based be of interest (249, 256). h novel tions include continuous analysis of on automatic termination of the coulometric method for the determina- acidic and basic components of process titration at the end point using tion of water in liquid ammonia has been gas streams (42) and alkalinity of aniperometric (215),potentiometric (13, presented by Klingelhoeffer (118). The water (265). Some continuous analyses 26, 109, 142, 231), or photometric water is reduced by potassium generated of metal ions, such as iron in water, (173) end-point detection methods. at a platinum cathode, and the end point using electrogenerated bromine (270), Several have been designed specifically located by the increase in conductivity and copper(I1) with electrogenerated for bromine number determinations associated with the formation of excess ferrocyanide ion (664) have also been (161, 173, 293). Hanamura (93) de- potassium dissolved in the ammonia. described. The determination of halide scribed a recording coulometric titrator. The method is sensitive to 1 to 100 ions with electrogenerated silver( I) (863) .In automatic, on-stream analyzer, de- p.p.m, of water. Several papers were and chlorine with iron(I1) (71, 262) have signed for the determination of SO, in concerned with the determination of been discussed. Barendrecht and Door- gases by titration with bromine has been water by adsorption on a Pz06film and nekamp (24) described the continuous discussed (25). An analyzer has been subsequent electrolysis between automatic determination of traces of designed to provide results directly in platinum electrodes (198, 247). A water by the Karl Fischer method. such terms as percentage or molarity similar technique was used for the deter- Takahashi (261) discussed the deter- (257). Several descriptions of devices mination of hydrogen in organic com- mination of relatively high concentra- for the automatic determination of pounds (9, 193, 246). By using this tions of substances by continuous coulo- plating thickness by constant current technique, 3-mg. samples containing metric methods. stripping of the plate and automatic about 3.2y0 hydrogen could be deter- Galvanic Analyzers. Further ex- termination of the stripping process mined with a standard deviation of tensions of galvanic cell analyzers for have been described (191, 212, 294). between 0.01 and 0.03%. oxygen have been discussed (186, 216). Potentiostats. Bewick and Fleisch- Miscellaneous Techniques. The Recent work has been concerned with mann (30) discussed in detail many of further use of pulse generation tech- investigations of cathode materials for the factors involved in the design and niques has been described (77, 131, more stable operation of the cell and performance of potentiostats. .ilthough 132). Voorhies and Davis (292) ex- both gold (192) and silver (156) elec- the discussion is mainly from the view- tended their interesting technique in- trodes have been recommended. Hersch point of potentiostats for measurements volving coulometry of substances ad- and Deuringer (103) devised a method of rapid electrode reaction rates, many sorbed on carbon black to the study of for the galvanic monitoring of ozone of the points discussed also apply to the electrode processes. The adsorptive based on the oxidation of bromide ion design of electronic potentiostats for properties of the carbon black is so high in a neutral medium. Because the coulometric work. Rooman and Hol- that reactants, products, and reactive current is related to the rate of supply brook (34)applied similar considerations intermediates remain quantitatively ad- of ozone to the electrodes by Faraday's to instruments more closely designed sorbed, and by current reversal tech- constant, temperature changes and cell for controlled potential coulometry. niques the rate of reaction of products geometry variations have no effect, and Besides describing the application of and intermediates can be determined. calibration with a standard source is not feed-back theory and stressing the The electro-oxidation of p-aminophenol, needed. Czuha, Gardiner, and Sawyer necessity of measuring electrolysis cell p-toluidine, and aniline were studied (56) reviewed the behavior of the parameters in the design of controlled using this technique. Cover and Pt-P20s-H20 system in the galvanic potential instrumentation, these authors Meites (52,53)described the application water analyzer. give detailed discussions of the electroly- of coulometric and automatic titrations Stripping Methods. Determination sis cells wed and of the effect of place- involving a constant rate of addition of of metal coatings by coulometric ment of the counter electrode and ref- reagent to the determination of rate stripping methods include A1 coatings erence electrode on the potential distri- constants from the shape of the (204)) Cd on steel and ropper-base bution over the electrode surface. Con- potentiometric titration curves. metals (165), Cr coatings over copper tinued descriptions of various potentio- Kozak and Fernando (I%?) studied and brass 1164) and nickel (f63),and Ni stats based on operational amplifiers the rate of the reaction of bromine and and Cu over brass (163). A stripping have appeared (39, 166); several stress phenetole by electrogeneration of bro- method for the analysis of such metal the application of solid state operational mine and observation of the rate of ions as Zn, Cu, and Cd, has been amplifiers (

76 R ANALYTICAL CHEMISTRY instruments based on operational current, but the linearity is rather poor (26) Barradas, R. G., Conway, €3. E., at the lower current values. Toren and J. Electroanal. Chem. 6. 314 11963). amplifiers. h mul1,ipurpose electro- (27) Baumann, F., Gilbert, 11. I)., ANAL. analytical a.pparatus for use in con- Driscoll (280) designed a digital read- CHEM.35, 1133 (1963). trolled current or cc’ntrolled potential out device for use with operational (251 Reronius, P., J. Phys. Chem. 67, applications, contair ing as principal amplifier-capacitor integrators. An 1391 (1963). (29) Berraz, b., Delgado, O., Rev. Fac. elements a potentios:at, a coulometer, operational amplifier switching device Ing. Quim., 7,’niv. Sacl. Litoral, Santa and a pH-meter relylator, has been is used to reset the integrator each time Fe, Arg. 29, 87 (1960). described (71). Other potentiostats, the voltage across the capacitor reaches (30) Bewick, il., Fleischmann, IZI., Elec- most dcsigned for‘ corrosion studies, a preset value, simultaneously tripping trochim. Alcta8, 89 (1963). (31) Bianchi, G.: Alazza, F., AIussini, have been designed (69, SO, 116, 216, a mechanical register. The relative T., Ibid., 7, 4%57(1962). %%I).Dugdale (6g) gives a useful com- error and standard deviation of the (32) Blackburn, T. R., Lingane, J. J., parison of several of the potentiostats method are said to be within 0.1%. J. Ekctroannl. Chem. 5, 216 (1963). currently in use, listing output currents Among the more classical coulometers, (33) Blevins, E. L., U. S. At. Energy and voltages, sensitivities, and response Helbig (100) discussed an ultraniicroti- Comm. CF-59-6-82, 4 pp. (1959). (34) Booman, C:. L., Holbrook, W. B., times. tration coulometer based on the pro- ANAL.CHEM. 35. 1793 11963). Propst (206) described an interesting duction of iodine, which is titrated with 135’1 Ibid.. D. 1986 scanning controlled potent’ial coulom- thiosulfate, and Van Soestbergen (690) (36) Brei&, 11. W., Electrochzm. Acta eter, which scans a potential range considered some aspects of the relation- 7, 601 (1962). (37) Breiter, AI. W., J. Electrochem. Soc. and records the coulombs. A novel cir- ship of gas production and current in 109, 425 (1962). cuit based upon a silicon diode allows the hydrogen-oxygen gas coulometer. 138) Breiter. 11. W.. Weinincer. J. L.. a scan rate which is an inverse function of the electrolysis cu:.rent. A network (39) Brown, It. H., U. S. At. Energy Comm. IDO-16862, 39 pp. (1063). to provide compensation for the faradaic ACKNOWLEDGMENT (40) Buck, I1 P., As.41,. CHEM.35, 692 (background) current, and charging of (1963). the double layer is also included. 41- The author is indebted to Sandra (41) Buck, R. l’., Crowe, T. J., Ibid., though it is moderately complex (in- Jackson for her aid in the preparation of p. 697. (42) Burnett, R. L., Klaver, R. F., Ibid., volving seven stab lized operational this manuscript. The support of the p. 1709. amplifiers), it, should be very useful for Robert A. Welch Foundation is grate- (43) Butler, C. G., hlartin, F. B., J. analysis of rnulticornponent systems. fully acknowledged. Pharm. Pharmacol. Sum... 14. 103T The increase in the a.;ailability of com- (1962). (44) Cahn, R. S., Cross, L. C., Ann. Rept. mercial potentiostats of various kinds Progr. Cherrc. (Cheiti. SOC.London) 59, during the past several years should LITERATURE CITED 450-99 (1962) Publ. (1963). lead to an even greater application of (45) Cavanagh, L. A., Coulson, D. M., controlled potential coulometric (1) Abresch, K., Buchel, E., Angew. De \.ries, J. E., Instr. Methods nul. Chem. 74, 685 (1962). Food Additives. Proc. Sumu..z ‘ Workshow methods. (2) Abresch, K., Buchel, E., 2. Anal. 1960, 195. Coulometers. Se.qeral groups si- Chem. 186, 175 (1962). (46) Charlot, G., Badoz-Lanibling, J., multaneously announced the applica- (3) Abresch, K., Claassen, I., “Die Coulo- Trernillon, B.,. “IClectrochemical Re- tion of voltage-to-frequency converters nietrische Analyse,” Verlag Chemie, actions, The ,hlectrochernical Methods C:.m.b.H., Weinheim, 1961. of Analvsis, Elsevier. Amsterdam. to coulometric deterlrtinati Ins (7,.8, 22, (4) Aikazyan, E. A,, Zh. Fiz. Khim. 33, 1962. 296). The basis of this integrator is a 1016 (1959). (47) Chatterjee, P. C., Bhattacharyya, commercially available voltage-to-fre- (5) Alfonsi, R., Anal. Chim. Acta 26, 316 H. P., J. Proc. Inst. Chemists (India)34, quency converter which will convert, (1962). 277 (1962). for (6) Altshuller, A. P., Sleva, S. F., AXAL. example, one volt input to an output (48) Christian, G. I).> Knoblock, E. C., CHEM.34, 418 (l!%2). Purdy, W. C., ANAL.CHEM. 35, 1869 signal of 10,000 count>sper second. By (7) Ammann, R., Desbarres, J., Bull. 1 1963). using this converter ‘:o measure the iR- SOC.Chim. France, 1962, p. 1012. (49) Ibid., p. 2217. drop over a standard resistor in the (8) Ammann, R., Desbarres, J., J. (50) Cokal, E. J., Wise, E. S., Ibid., Electroanal. Chem. 4, 121 (1962). electrolysis circuit an’i feeding the out- 35, 914 (1963). (9) Anisimova, G. F., Klomova, V. A,, (51) Courtot-Coupez, J., Acta. Chim. put to a scaler, the cu-rent-time integral Zh. Analit. Khim. 18, 412 (1863). Acad. Scz. Hung. 32, 207 (1962). (10) Anson, F. C., J. Electrochem. SOC. is obtained. Although, as has been (521 Cover. R. E.. Meites.,, L.. J. Phus. pointed out by Boorrtan and Holbrook 110, 436 (1963). Chem. 67; 1528 (1963). (11) Anson, C., King, D. SI., ANAL. (Sg), t’he voltage-to-frsquency converter F. (53) Ibzd., p. 2311. CHEM.34, 362 (1962). (-54)Cserhegyi, A,, Horanyi, Gy., Nagy, is based on an in.;egral operational (12’) Anson, F. C., Schultz, F. A,, Ibid., F., Magy. Kem. Folyoirat 69, 245 amplifier, so that the, overall accuracy 35, 1114 (1963). (1963). of the apparatus can 3e no greater than (13) Babenyshev, V. M., Khvoinitskil (55) Cuta. F., Ju. Y. C.. Rev. Chzm.. V. Zavodsk. Lab. 113 (1960). that of an operational amplifier-capa- I., 26, Acad. Rep.’ Populairs ’Roumaine 7; (14) Balaschova, N. A., Electrochim. Atta 127 (1962). citor integrator, the xcuracy of these 7. 559 11962’1. (56) Czuha, AI., Gardiner, K. W., Sawyer, coulometers is about O.Olyc, which is (15i Barbi, G.’ B., Comzt. lYazl. Energza D. T., J. Electroanal. Chem. 4, 51 certainly sufficient for most coulometric AY~~~l.C.YI-88, 12 pp. (1961). (1962). (161 Bard, A. J., ANAL.CHEY. 35, 340 (.57) Dahms, H., Green, AI., J. Electro- analyses. ;in integrator of this type has (1963). performed very satisfactorily in the chem. SOC.110. 1075 11963). 117’1 Ibid..,I D. 1125 (58) Dalirns, H., Cheen, AI., Weber, J., author’s laboratory For the past few (18) Ibid., p. 1602. .Yature 196, 1310 (1962) years. (19) Bard, A. J., J. Electroanal. Chem. (59) Dapo, R. F., llann, C. K., ANAL 3, 117 (1962). CHEM..35, 677 (1963). Schoedler (2‘29) described a new (20) Bard, A. J., Mayell, J. S., J. Phys. integrator based on a d.c. potentio- (60) Davis, I>. G., Ibid., 35, 764 (1963). Chem. 66, 2173 (1962) (61) Davtyan, 0. K., 51is?.uk, E. G., metric controller which controls an (21) Bard, A. J., Petropoulos, A. G., Zh. Fiz. Khim. 36, 673 ( 1962). electromagnetic encoder in such a Anal. Chim. Acta 27, 44 (1962). 122) Bard, A. J., Solon. E.. ANAL.CHEY. (62) I>elgado, 0. A,, Rev. Fuc. Ing. Quim., manner that pulses originating in a 34. 1181 119621. C‘niv. .Yncl. Litorul, Santa Fe, rlrg. quartz oscillator are ff,d to a counter at (23) ’Bard, A. J., Solon, E., J. Phys. Chem. 30. 83 119611. (63) ’Ibid.,~p. 101. a rate proportional to the current 67.r 2826~ ~ (1963).~--- (64) Delvin, W. L., Iluncan, 1,. It., U. magnitude. The precision of t’his (24) Barendrecht, E., Doornekamp, J. 8. G. F.. Z. Anal. Chem. 186, 176 (1962). At. Energy Comm. HCV-71436, 8 pp. integrator is about 0.3% for currents (25) Barendrecht, E., Jlartens, W., ANAL. (1961). down to one hundredth of the full-scale CHEM.34, 138 (1962) (65) Ibid., HW’-S.4-26;36, X pp. (1963)

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VOL. 36, NO 5, APRIL 1964 79 R