Polarographic theory, instrumentation, and methodology

Polarographic Theory, Instrumentation, and Methodology Richard S. Nicholson, Chemistry Department, Michigan State University, East Lansing, Mich. 48823

HE NEW BYLINE is the third since T t h i s particular review began. David Hume has written it since 1956, which is a long time to do something like this. The present review follows much the same pattern set by Hume (96), selectively covering literature from January 1968 to approximately December 1969. The review is concerned primarily with classical polarography and related techniques, while papers on electrode processes and more esoteric topics will be presented elsewhere. Several books and review articles worthy of mention have appeared since the last review. Bn introductory textbook on polarography for chemistry students by Heyrovsky and Zuman (91) has been translated into English, and Mairanovskii’s book (127) on catalytic and kinetic polarographic waves has been translated from Russian. Adams has published a book on solid electrodes ( I ) , which should be of interest to all polarographers. A book devoted to the polarography of metal complexes has been published by Crow (50). The third volume of the very useful “Electroanalytical Chemistry,” edited by Bard (9) has been published. This latest volume contains at least two chapters, cited specifically later, which should be of interest to readers of this review. Although not strictly within the scope of this review, the chapter by Anson (5) makes interesting reading, while the chapter in the same series by Patterson (169) is more closely in line with the topics of this review. Finally, for those concerned about relevance in their research, a review article by Palecek (168) on the use of polarography in nucleic acid research may be of interest.

CLASSICAL POLAROGRAPHY

Instruments and Apparatus. For t h e instrument builders, a review by Fisher (71) of t h e general principles for obtaining maximum signal-to-noise ratios is worth reading. Several illustrative examples are cited, including dc polarography. Although directed toward fast potentiostatic measurements, a lucid review by Schroeder and Shaiii (194) also is worth studying. They have summarized feedback principles and elementary control circuit theory, as well as the principles of matching cells and in130R

struments t o achieve optimum response a n d stability. I n terms of actual instruments, the trend toward making them (presumably) smaller and more solid state continues. Bezman and McKinney (20) have described a transistorized polarograph which possesses reasonably good dynamic characteristics. They include a detailed analysis of the dynamic response of the instrument based on a simple equivalent circuit dummy cell. They also described a versatile ramp and triangular-wave generator which is designed with computer compatible digital logic circuits. Fisher, Belew, and Kelley have constructed a derivative polarograph (72), as have Jones et aE. (106). Dryhurst, Rosen, and Elving (63) have described solid-state modular instrumentation suitable for polarography and related techniques. Devices for controlling the drop-time of a D M E by mechanically dislodging drops continue to be published. The most novel of these is described by Kurosaki (119) who used a barium titanate ceramic strip attached to the capillary, and the piezoelectric effect to dislodge drops. Mairanovskii has found that with his drop-knocker (128) limiting currents agree with Koutecky’s equation to &2.7y0for drop-times less than one second, and to +0.7y0 for longer drop-times. Belew et al. (12) claim some advantages for knocking drops from a Smoler electrode. Although not usually the serious problem with polarography that it is with some transient techniques, ohmic potential losses can still annoy the polarographer. Thomas and Schaap (220) have published a detailed analysis of the effects of uncompensated iR losses in nonaqueous polarography and on the measurement of half-wave potentials. They described a graphical method for extrapolation of residual currents in the presence of large ohmic distortions. Rritz and Bauer (SO) have calculated theoretically the resistance between a D h l E and a large counter electrode, taking into account the presence of the capillary. Taylor and Barradas (227) pointed out a n error in the calculations of Britz and Bauer, and found that newly calculated resistances agree well with the experimental data of Britz and Bauer. The use of positive feedback for electronic compensation of iR drop has been analyzed theoretically by Brown et al. ( S 4 ) , Pilla et al. (175), aiid Bewick ( 1 7 ) . Brown

ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970

et al. (33) applied some of these theoretical guidelines to the ac polarography experiment and reported good results. There are relatively few new ideas for polarographic cells. Arthur, Rulison, and Berlin (6) suggested that it is sometimes wise to use a D M E for macroscale electrolyses, and therefore they designed a cell which can be flushed with nitrogen and hermetically sealed, so that you can polarograph away for ten days or so. Smoler (205) has described a cell in which the counterreference electrode is separated from the electrolysis compartment by a closeable contact. Differences in density prevent mixing of the two solutions. Mal’ kov (131) has described a flow-through cell designed for continuous electrolytic purification of electrolytes. Either mercury or carbon electrodes can be used with the cell. Forno (75) has described a two-stage flow cell for use with ESR spectroscopy and relatively short-lived radicals. Reference Electrodes. Tsuji and Elving (224) have discussed the conversion of polarographic data obtained with a given reference electrode to a different reference electrode scale. The major point seems to be the obvious one that with different solutions the pre;.-ence of liquid junction potentials will affect such interconversions. These authors reported some experimental data substantiating this point, and suggested a standard experimental procedure for making interconversions. Bravo and Iwamoto (26) have described a nonaqueous calomel electrode suitable for use in acetonitrile. The electrode consists of calomel in acetonitrile contaiiiing potassium chloride and potassium perchlorate (both are sparingly soluble) and 0.10F tetraethylammonium perchlorate. The electrode is reported to be stable, reproducible, unaffected by small amounts of water, and essentially nonpolarizable for current densities of 2.0 p A emd2 or less. Piljac and Iwamoto (17‘4) also investigated a nonaqueous calomel electrode in propylene carbonate containing 0.10F tetraethylammonium perchlorate. Although the electrode potentials are reported to be stable aiid reproducible, the electrode is easily polarized and cannot be used as a counter electrode in polarographic experiments. Burrows and Jasinski (37) investigated lithium as a reference electrode in propylene carbonate. They found that a ribbon of pure lithium metal in 1.OM lithium

perchlorate gives reproducible, stable potentials even in the presence of water. Their data imply t h a t the electrode is essentially nonpolarized for current densities less than about 2 fi-4 cm-2. Standard potentials for silver-silver chloride electrodes have been reported for N,N-dimethylacetamide by Scrosati, Pecci, and Pistoia (195), for formamide by Broadbank et al. (SI),and for sulfolane-water mixtures by Tommila and Belinskij (223). Fleischmann and Hiddleston (73) have described a probe electrode which they suggested for use in place of the conventional Luggin capillary. The electrode consists of a fine paladium wire sealed in soda glass. The tip of the paladium is ground flat, the wire is electrolytically saturated with hydrogen, then washed and air dried. The electrode is reported to give a stable, reproducible potential of 50mV us. a hydrogen electrode. B n obvious ndvantage of such a n electrode is its low impedance compared with a Luggin capillary. Half-Wave Potentials. A popular thing for polarographers t o d o is generate straight lines by plotting halfwave potentials as ordinate us. something else as abscissa. J u s t about everything conceivable has been used for t h e abscissa b y now, usually with success. The literature in this area over t h e past two years does make one thing abundantly clear, namely t h a t with few exceptions the old standbys of Hammett-like and molecular orbital parameters give these linear correlations as well as ever. Unfortunately, correlations with 310 theory seem to work regardless of the quantum mechanical sophistication employed in the calculations. Of course, this fact has its good points because any electrochemist can perform HMO calculations, and there are some interesting things t h a t can be done with the results. A good example of this is given by Carsky and Zuman (40) who used HMO theory to explain and predict the course of the electrolysis of some substituted benzonitriles. There is some evidence of applications of polarography in the area of energy transfer and excited states. For example, Mazzenga et al. (142) have discussed briefly the relationship between half-wave potentials and photochemically excited states, and were able to show a linear correlation of half-wave potentials with triplet energies for a series of hydrocarbons. They pointed out that such correlations may provide a useful means of estimating triplet energies. Loeber (126) has published ground state and first excited singlet state half-wave potentials for a series of substituted aminoquinols. Half-wave potentials for the excited state were calculated from fluorescence data and

ground state polarographic data. Stutter (215) has presented electrochemical theory for a n experiment designed to measure half-wave potentials of excited molecules, while Maricle and Maurer (136) have described an experiment which may permit measurement of redox properties of electronically excited molecules. Hale (85) also has discussed the electrochemistry of molecules in electronically excited states. Along more pedestrian lines, there naturally have been many polarographic determinations of equilibrium constants published during the last two years. The subject has been reviewed by Verdier and Piro (228), and by Seth and Naqvi (196). h paper by Momoki, Ogawa, and Sato (154) is a good example of the extent t o which statistical methods can be used in analyzing polarographic data. Finally, Breslow and Balasubramanian (29) have described a clever application of electrochemical data to estimation of pK, for triphenylcyclopropene. Reversible half-wave potentials were determined with cyclic voltammetry and chronopotentiometry, and then employed in a thermodynamic pseudocycle to calculate the equilibrium constant. The authors state that the equilibrium constant is inaccessible by other means. Currents. The theory of polarographic currents, including coupled reactions, adsorption, and double layer effects, has been reviewed by K o r y t a (114). Bewick and Thirsk (18) discussed the use of polarography in the mechanistic study of consecutive electrode processes. Oldham (161) has published what he calls a unified treatment of electrolysis at a n expanding mercury electrode. What this means is that the diffusion problem is formulated in terms of a n electrode for which area varies as an arbitrary power of time. General equations are derived from this model for both controlled potential and controlled current electrolysis. The results naturally reduce to many well known cases, including the Ilkovic equation. One result of the treatment is the prediction t h a t if electrode area were to vary as the square root of time, then current-potential curves should be time independent. While it is likely that someone with an engineering bent will construct such a n electrode, it doesn't seem likely that i t would have any significant advantages, analytical or otherwise, over an ordinary DhlE. I n a different paper Oldham (162) has discussed briefly what he describes as a new approach to solving diffusion problems. What this involves is reducing the Fick equations to an ordinary differential equation (not as ordinary as you might think, however) without using the boundary condition corresponding to the electrode surface.

Given a boundary condition, it can be incorporated in the differential equation and (hopefully) solved. Of course, whenever a solut'ion can be obtained by this approach, exactly the same result could be derived directly from the Fick equations. Xevertheless, Oldham's approach may have some definite advantages, especially for problems t'hat a t some point must be solved numerically. The approach seems analogous to the now common procedure of writing Fick's law as a n integral equation (Duhamel's theorem) and then incorporating the surface boundary condition. For problems that must be solved numerically, this procedure has proved to have some real advantages. And when this kind of math gets too hairy, one can always go to a sure-fire method like digital simulation, which Feldberg in particular has employed very successfully. Digital simulation, which seems to be a euphemism for finite difference, has been described in detail by Feldberg (66). Even with the possibility of t 1 : 2 electrodes, the D M E likely will be around for some time, and therefore two papers by Duda and Vrentas (64, 65) are u-ort'hy of mention. These authors have solved the diffusion problem for an expanding spherical electrode with a n arbitrary time-dependent mercury flow rate. Except for effects like depletion and stirring with drop detachment, their results (a power series) are the most rigorous to date for the DlIE. They have coupled t h i j equation with a mathematical analysis of the time dependence of the mercury flow rate for a conventional feed system. The resulting expression for instantaneous currents is compared with available experirnent'al data, showing that their theory is an improvement, but still not perfect. When the attendant mathematical difficulties of a n accurate description of electrolysis at a D l I E are considered, it seems safe to conclude that stationary electrodes also are here to stay. As for kinetics and polarography, Oldham and Smith (163) have discussed two different empirical approximations t'hey had independently published earlier for t,he Koutecky function. These authors compared the accuracy of each approximation and jointly agreed on the relative merits of each. Birke and Xarzluff (23) have derived polarographic theory for a second order catalytic mechanism, with which rate const'ants reportedly can be calculated with an uncertainty of 1%. An experimental application of t,he theory is included in their paper. Birke (22) also has derived polarographic t'heory for a complex mechanism involving both catalytic regeneration and dimerization. He used the theory to invest'igate t'he reduction of vanadium in the presence of chlorite. Fischerova, Dracka, and


131 R

Meloun (70) developed theory for an irreversible reduction followed by a chemical reaction with the product oxidized a t a more negative potential than the initial reduction. Their theory was applied to the reduction of two different chromium complexes. Tur’yan (?226) has derived equations for a catalytic mechanism involving bimolecular surface reactions; the analysis is based on reaction layer theory. Reaction layer theory also was employed by Janata and hlark (101) t o treat an E C E mechanism where the chemical step is second order. They used the theory t o evaluate the influence of proton donor on the reduction of anthracene. Speaking of the E C E mechanism, Kastening (108) has pointed out that he and Holleck were the first t o derive E C E polarographic theory. Gelb (79) has developed theory for the case of a reversible dimer to monomer reaction with adsorption of both dimer and monomer. Laviron (123) has derived an expression to account for adsorption induced prewaves and postwaves; the theory is said to describe quantitatively the methylene blue prewave. Holub and Xemec (92) have discussed the use of a n analog computer to solve problems involving adsorption at a D N E . For those who worry about adsorption and like t o think about chemistry on a molecular level, a paper by Smith (203), although not directly related to electrochemistry, makes interesting reading. I n terms of limiting currents and analysis, Lingane (125), and Matsuda and Tamamushi (141) have suggested long-term integration of limiting currents. Lingane talks in terms of obtaining accuracy and precision of the order of O.l%, while Matsuda and Tamamushi talk in terms of trace analysis. The latter authors suggested the use of twin cells to compensate for charging current, since with integration i t is unnecessary to synchronize the two dropping electrodes. Ruzic and Branica (189, 190) have described a rather complicated graphical and logarithmic procedure for analysis of overlapping reversible or irreversible polarographic waves. RELATED TECHNIQUES AND TOPICS

Chronopotentiometry. The advertised advantages of chronopotentiome t r y are experimental and theoretical simplicity. The major disadvantage, and it’s a big one, is the fact t h a t t h e experimentally controlled current is partitioned between the faradaic and double-layer charging processes. The result in general is distortion of experimental chronopotentiograms with respect to things like the Sand equation where double layer charging is not considered. Unfortunately, to include 132

R

double-layer charging in the mathematical model increases the complexity of the theory, so much so that prior to 1968 the problem had not been attacked with any theoretical rigor. I n 1968 three groups independently published mathematical analyses for essentially the same model: linear diffusion, reversible electron transfer, potential independent double-layer capacitance, and charging as though the electrode were ideally polarized. Rodgers and Meites (186) used finite difference to solve the partial differential equations. They also included the case of totally irreversible electron transfer. DeVries (56, 57), and Olmstead and Kicholson (166) calculated potential-time curves by solving numerically the appropriate nonlinear integral equation. The latter group included in their treatment the case of current reversal. The upshot of these papers seems to be that chronopotentiometry is not much better off than it was before. For example, analysis of theoretical chronopotentiograms by the common methods of transition time measurement shows that none of these methods works very well if the objective is a posteriori double-layer charging compensation. Olmstead and Nicholson did find that a method due to Laity and McIntyre was able accurately to extract transition times corresponding to the Sand equation. Unfortunately, the method is not very convenient to use, and moreover the extent to which it works presumably is a function of the electrolysis mechanism. Thus, all things considered, using chronopotentiometry is a complicated business at best, and it hardly seems worth the trouble in view of the convenience of some other electrochemical techniques. Nevertheless, de Vries has treated theoretically the case of doublelayer charging with chronopotentiometry a t mercury film electrodes (58), and also the case of programmed current chronopotentiometry (59). Not surprisingly, he finds that programmed current offers no real advantages over constant current. Dracka (62) also has published a theoretical analysis of double layer-charging and a preceding chemical reaction. He analyzed various methods of transition time measurement, including a new graphical one of his own. Dornfeld and Evans (60) have published a general theoretical treatment of chronopotentiometry at cylindrical electrodes. Their results predict a small increase in analytical sensitivity for electrodes of small radius. Bos and van Dalen (24) have derived theoretical expressions for electrolysis with current reversal of amalgam forming metals on a mercury film electrode. Fischer, Dracka, and Stenina-Jakovleva (69) have dei7eloped the theory of chronopotentiometry when the reduction prod-


uct is converted chemically into a substance that is oxidized at the same potential. They applied the theory t o reduction of a chromium chloride complex. Herman and Bard (90) have extended the theory of cyclic chronopotentiometry to include the common coupled chemical reaction sequences. They illustrated the theory by applying it to the electrochemist’s cadmium of the E C E mechanism (p-nitrosophenol). Beyerlein and Nicholson (19 ) have derived a simple relationship between overpotential for cyclic chronopotentiometry and the electron transfer rate constant. Again, double-layer charging represents a major limitation of the method. Kies (109) has described a circuit which programs current for use with a D M E in such a way that current density is essentially constant during the life of a drop. Sturrock, Anstine, and Gibson (214 ) have discussed analytical applications of derivative chronopotentiometry to multicomponent systems. Campbell (39) has used the transient nature of chronopotentiometry to measure thermodynamic properties of plutonium nitride a t temperatures where plutonium reacts rapidly with nitrogen. Peters and Kinjo (172) have analyzed the feasibility and accuracy of determining halides and mixtures of halides by chronopotentiometry with silver anodes. Bowman and Bard (16)have suggested using controlled potential electrolysis prior to chronopotentiometry. The idea is that with multicomponent systems prior electrolysis should reduce the well known effect of more easily electrolyzed components on following chronopotentiometric waves. The approach should have little appeal to those analysts who still have a polarograph in their lab. Although not in English, Tvrzicka and Dolezal (226) have reviewed the topic of chronopotentiometry with a n extensive bibliography. Alternating Current Polarography. Breyer (36) has reviewed ac polarography and tensammetry. Smith and &Cord (104) have pointed out that theoretically an ac polarographic response is expected for totally irreversible electrode processes, regardless of the source of irreversibility (electron transfer, chemical reactions). Salikhdzhanova and Zhdanov (191) have considered theoretically the influence of mercury column height for both reversible and irreversible systems. They also described experiments on reduction of nickel which confirm their theoretical ccjnclusions. Smith and coworkers (143, 145, 147) have extended the rigor of ac polarographic theory for coupled chemical reactions. Their calculations are now based on an expanding plane model for the DME. McCord and Smith (148) have tested experimentally the theory (144) of second harmonic ac polarography for quasireversible sys-

tems. They studied a chromium cyanide complex and (naturally) cadmium, and found good agreement between theory and experiment. These same authors (246, 149) also have published second harmonic theory for coupled reactions and an expanding plane model. They found that second harmonic polarography possesses special advantages for studying chemical reactions following electron transfer. Randles and Whitehouse (181) also have studied second harmonics theoretically and experimentally. Tensammetry has been reviewed by Jehring (102). Jehring et al. (103, 104) have used the polyethylene glycol system to compare the analytical sensitivity of several variations of the tensammetry experiment] including phase selective and second harmonic detection, differential measurements with two dropping electrodes] and the use of stationary electrodes. Some of these methods reportedly enhance sensitivity by an order of magnitude over classical tensammetry. Bauer, Campbell, and Shallal (10) have explained anomalous tensammetric behavior of amyl alcohol as resulting from a salting out effect. Jacobsen and Tandberg (100) have employed an anionic surfactant to mask ac polarographic waves of negatively charged metal citrate complexes. They were able t o determine cadmium in the presence of a 10,000-fold excess of indium with this trick. Ramaley and Krause (180) have published the theory for a technique they call square wave voltammetry. The method consists of applying to a stationary electrode a small amplitude square wave synchronized with a staircase potential sweep. Interference of double-layer charging is minimized by proper timing of the current measuring operation. The same authors (118) have evaluated the technique experimentally, and reported good agreement with theory as well as high analytical sensitivity. Chronoamperometry. This subject has been reviewed by Saveant (192), who discussed both single and cyclic triangular wave potential scans. Rlastragostino and Saveant (139) have published an extensive theoretical analysis for the single scan method and variants of the E C E mechanism. The same paper includes theoretical calculations for the disproportionation reaction, which also was discussed by Olrnstead and Nicholson (166) for cyclic scans. In a subsequent paper Mastragostino and Saveant (140) applied their theory to the well known disporportionation of uranium. They found that an E C E pathway also is possible, and that under some conditions it is kinetically important. Theory has been published by Olmstead, Hamilton, and Xicholson (164) for a following dimer-

ization reaction, while Voloshin (229) has considered higher-order preceding reactions. Shuman and S h a h (202) also have considered the theory of cyclic voltammetry for preceding reactions. They applied results of their theoretical calculations to a kinetic and mechanistic study of the reduction of the cadmium nitrilotriacctic acid complex. The effect of adsorption has been calculated theoretically by Nesterov and Korovin (160), and by Laviron (122). The former authors applied their theory to oxidation of hydrazine, while the latter author investigated dipyridylethylene and reported good agreement with theory. The theory of stationary electrode polarography including uncompensated iR drop has been extended to totally irreversible electron transfer by Roffia and Lavacchielli (186). Their theory was tested experimentally by reduction of bromite on a hanging mercury drop electrode. Caselli, Ottombrini, and Papoff (41) have included the influence of doublelayer charging in a theoretical analysis of the single scan method. Their theory was checked by the reduction of zinc in several different types and concentrations of supporting electrolyte. Shuman (201) has derived theory for cyclic scans and nonunity electrode reaction orders. He reported good agreement between his calculations and oxidation of mercury in dilute cyanide solutions. Meyers and Shain (157) have shown how half-wave potentials can be calculated from experimental peak and half-peak potentials for two unresolved waves. Their discussion is based on earlier calculations of Polcyn and Shain who assumed that both electron transfers are reversible. Mueller (155) has discussed the minimum separation of half-wave potentials required for quantitative analysis with overlapping waves. His discussion also is based on the assumption of reversible electron transfer, and includes first and second derivative readout techniques. Nelson (159) has suggested a method for distinguishing between simple multielectron transfer processes and the corresponding E C E reaction where the chemical step is very rapid. Oxidation of 4-nitrotriphenylamine, which is an E C E process, is used as an illustrative example. Malachesky (129) has described a simple method for determining n-values, based on comparing single sweep data with data from constant potential electrolysis. The method does not require knowledge of diffusion coefficients, concentration, or electrode area, and is reported to give accurate results for several compounds. Stephens and Harrar (208) have investigated analytical applications of second derivative digital readout for rapid scans. They reported reproducibility of 0.1% for concentrations greater

than 1 0 - 4 ~and 1% for concentrations greater then 10-5M. They also calculated theoretical curves and found good agreement with experiment. Mueller and Jones (156) have described an instrument designed for both controlled potential and controlled current electrolysis. The instrument includes a versatile function generator] and hence is suitable for cyclic voltammetry. Huntington and Davis (97) have published circuits for a simple yet versatile triangular wave generator, employing only two operational amplifiers. Slopes for the triangular wave are independently adjustable, a wide range of scan rates is provided, and the instrument operates in either single cycle or free running modes. Brown (32) also has published the circuit of a sweep generator suitable for voltammetry. Design of the sweep generator is based on analysis of the response of a potentiostat to a ramp excitation. Apparently the ultimate in instrumentation these days is t o have your own digital computer in the lab. Perone et al. (170) have used this instrument for acquisition of analytical data in connection with fast sweep polarography and derivative readout. They also used the computer for ensemble averaging, which they found extended the analytical sensitivity about tenfold. Perone, Jones, and Gutknecht (171) are a little more sophisticated, and give a good example of how the high speed decision making capabilities of a computer can be used to advantage by real time communication between the experiment and computer. I n their example they considered the possibility of minimizing the interference of preceding reduction steps in a multicomponent system by introducing a hold in the potential scan just after the peak for a given reduction. The actual interrupt potential and length of the hold are computed in real time on the basis of data received by the computer during each reduction step. They reported significant improvement in the quality of analytical data obtained with this system. Inverse Polarography. This technique] also known as amalgam polarography and stripping analysis, has been reviewed by Hrabankova and Dolezal (93) ; although not in English, the bibliography is extensive. Stromberg et al. ($13) have discussed the maximum theoretical sensitivity of stripping analysis, and also the theoretical basir for increasing the sensitivity of a given analysis. They cited the determination of bismuth as an illustration of using theory t o select optimal experimental conditions. Stromberg and Baletskaya (219) have used the stripping of zinc from a silver wire with a 5-p mercury surface layer to confirm the theory of Stromberg.


0

133 R

Baletskaya, Zakharova, and Zakharov ( 7 ) have used stripping analysis to determine the solubility of copper in mercury, and obtained a value in agreement with the literature. Alimarin et al. (4) have investigated the effect on stripping analysis of the metal used to contact a hanging mercury drop electrode. They employed silver, gold, and platinum contracts in the determination of indium, and analyzed their data statistically. Their results indicated that an intermetallic compound is formed between indium and a gold contact. Krasnova and Zebreva (117) also studied the effect of contact material and found that sensitivity for determination of zinc and cadmium is greater with silver than with platinum contacts. Koster and Ariel (116) have described an electrode consisting of a 10-1 layer of nickel electrolytically deposited on platinum, which is then dipped in mercury to form a 2- to 3-1 mercury film. The electrode is said to require very short pre-electrolysis times, and to have keeping qualities superior to a mercury coated platinum electrode. Tindall and Bruckenstein (222) have used a ring-disk electrode to determine copper and silver simultaneously by stripping analysis. Kodama and Noda (111) have used ac polarography for stripping, while hlizuike, Miwa, and Oki (153) have used square wave voltammetry. I n each case, an enhanced sensitivity over conventional methods was reported. Christian (42) found that pulse polarographic stripping of cadmium increases sensitivity one order of magnitude over the conventional method. He also studied the effect of supporting electrolyte concentration with pulse polarographic stripping, and found that low concentrations of electrolyte could be employed. Galus, Kemula, and Sacha (78) have derived theoretical equations for stripping by chronopotentiometry, and claim there are conditions under which that technique is preferable to linear potential scan. Disk and Ring-Disk Voltammetry. The popularity of disk and ring-disk voltammetry is still on t h e up-swing. Filinovskii and Podgaetskii (68) have discussed the theory of irreversible reductions on a rotating disk electrode. The ubiquitous E C E mechanism has been considered by several authors. For example, Filinovskii (67) derived an expression for limiting current a t a rotating disk and indicated how to evaluate the rate constant for the chemical step. Karp (107) published an extension and improvement of a theory for rotated disk first introduced by Xalachesky et al. (1966) for the E C E mechanism. Llarcoux, Adams, and Feldberg (135) have treated theoretically (digital simulation) several variants of the E C E mechanism for the 134R

rotated disk. When the chemical step is first order and irreversible their presumably more exact results are identical to Karp’s. The same authors also included the case of a succeeding dimerization. They applied their results t o experimental determination of rate constants for dimerization of several substituted triphenylamines. Ulstrup (227) has published equations for a disproportionation reaction initiated at a rotating disk, a mechanism which is included in the paper by Marcoux, Adams, and Feldberg. Malachesky et al. (130) have investigated the use of ring-disk electrodes to measure rates of chemical reactions initiated a t the disk. Their approach is a n empirical one in which they employed chemical systems with known rate constants to calibrate the ring-disk electrode. They constructed a working curve by plotting the ratio of ring to disk current us. k / w 1 / 2 ( k is the rate constant for the chemical reaction and w is the rotation speed). I n the long run this kind of approach may prove to be as useful as any. 91bery, Hitchman, and Ulstrup ( 2 ) have published an elaboration of their theory for ring-disk electrodes and second order chemical reactions initiated electrolytically. Their theory was used to measure the rate constant for bromination of allyl alcohol; the value they obtained agrees with the accepted value. The theory of adsorption processes a t ringdisk electrodes has been discussed by Bruckenstein and Xapp (35). They also studied the adsorption of copper(1) on platinum, and reported excellent agreement between theory and experiment. Tindall and Bruckenstein (221) have shown that it is possible to measure heterogeneous equilibrium constants with ring-disk voltammetry. They used the reaction of copper with copper(11) in sulfuric acid as an illustrative example. Albery and Ulstrup (3) have employed ring-disk voltammetry to evaluate the current distribution on a rotating disk electrode. They compared their results with Newman’s convective-diffusion equation and concluded that in some cases migration also is important. Nekrasov and Korsun (113, 158) have combined ring-disk voltammetry with ESR spectroscopy to generate and identify intermediates formed in the reduction of aromatic carbonyl compounds. Maloy, Prater, and Bard (133) have shown that the rotating ring-disk provides a convenient system for generating and studying elect rochemiluminescence. One of the unattractive features of rotating disk and ring-disk voltammetry is the hardware that is required. Although discussions of hardware design frequently are included in papers not cited in this review, some papers devoted specifically to hardware are


worthy of mention. If two electrodes in close proximity (ring and disk) are good, then three ought to be even better. This system is now available in the form of the split-ring-disk electrode described by Miller (152). His electrode is a conventional ring-disk where the ring section is split into two half rings. The potential of the three electrodes can be controlled independently with operational amplifier circuitry described by Miller. Miller used the electrode to study the anodic behavior of copper-zinc alloys, but it’s not difficult to imagine more esoteric applications. Doronin (61) has published the design of a ring-disk electrode, which is said to provide easy exchange of the disk section. A cell with a controlled atmosphere suitable for rotating disk studies in fused salts has been described by Zambonin (233). Given a cell and electrode, all that’s left is to get the electrode spinning. Variable speed drive assemblies have been described by Sonner, hliller, and Visco (206), and by McIntyre and Peck (160). The rotation speed for the system described by the latter authors can be conveniently programmed with any arbitrary voltage waveform. Along similar lines, Creason and Nelson (49) have described briefly a tachometer-function generator combination which provides a direct plot of limiting current us. the square root of rotation speed. Nonaqueous Solvents. Mann (134) has contributed a very useful review of t h e properties, purification, and applications of most nonaqueous solvents of interest to electrochemists. Reid and Vincent (182) have published an extensive review of electrochemistry in the six (structurally) simplest amide solvents. Breant and Demange-Guerin (28) have reviewed chemical and electrochemical properties of dimethylformamide. Sherman and Olson (200) have described a relatively simple procedure for purifying acetonitrile, which is said to give a product of electrochemical purity comparable to other published purification methods. The degree of association of supporting electrolytes in acetonitrile has been evaluated from conductivity measurements by Forcier and Olver (74). They rereported that the commonly used tetraethylammonium salts are completely dissociated. Since these same quaternary ammonium salts are such useful electrolytes for nonaqueous electrochemistry, Texier and Badoz-Lambling (219) have investigated the possiblity of using them as solvents for polarography and voltammetry. Although these particular salts certainly are here to stay as electrolytes, apparently they’re never going to make the headlines as solvents. Breant et al. (27) have investigated the electrochemical

behavior and useful potential range of N-methylpyrrolidinone, and reported that its behavior is similar to dimethylformamide in many respects. Desbarres, Pichet, and Benoit (55),and Benoit, Guay, and Desbarres (13) have inveitigated sulfolane as a solvent for electrochemical studies. They determined the useful potential range under a variety of conditions, and also estimated solvation energies of halide ions by means of the ferrocene couple. Use of sulfolane for polarography also has been studied by Martinmaa (138) who employed the solvent for ESR spectroscopy. Coetzee, Simon, and Bertozzi (44) have developed and evaluated a purification procedure for sulfolane. They also observed anomalous behavior of polarographic currents during the life of a drop, which they attributed to the high viscosity of the solvent. The same authors concluded from polarogram5 of rubidium that the liquid junction potential between an aqueous SCE and 0.1-11 tetraethylammonium perchlorate solutions of sulfolane does not exceed a few hundredths of a volt. Jones (105) has described polarographic measurements in butyl phosphate. Gutniann and Duschek (81) have studied the polarographic behavior of several transition metal ions in ethylene sulfite. They also investigated the effect of water added to the solvent. The polarography of transition metals in hydrazine has been described by Goudeau et al. (80). Gutmann and coworkers (21, 82-84) have studied the polarography of metal ions in propylene carbonate. Alkali metal ion reduction in propylene carbonate has been investigated by Kuznetsov, Vasil’kevich, and Damaskin (121). They estimated cation solvation energies from polarographic measurements, and reported good agreement with literature values. Diverse Electrode Systems. The quest for new electrode systems, or new wrinkles for old ones, is still actively in progress. Berge and Struebing (15) have described the continuous mechanical reactivation of a platinum electrode surface by a rotating ceramic cylinder. They studied several inorganic systems and found that half-wave potentials are independent of rotation rate of the cylinder and as reproducible as those obtained with a DME. They reported a relative standard deviation for the limiting current of 2%. These authors (16) also used the same approach with paraffin-impregnated carbon electrodes. I n this case, they reported a standard deviation of limiting current for 94 current-voltage curves of 1.5y0. Hartley, Hiebert, and Cox (88) have described a method for electrolytic preparation of platinum based mercury film electrodes of known film thickness.

The life expectancy of the electrodes is said to be of the order of several days, with hydrogen overvoltage approaching that of a hanging mercury drop electrode. They also suggested that the method is useful for preparing rotating mercury electrodes. Robbins and Enke (184) have employed X-ray diffraction to investigate the compound formed a t the platinum-mercury interface, and concluded that it has the stoichiometry PtHg,. Mal’kov (132) has described a procedure for preparing mercurygraphite electrodes, and reported that the electrodes functioned satisfactorily for six months. Scarano et al. (193)have studied the properties of the rapidly dropping Smoler electrode in some detail. They reported deviations from the Ilkovic equation of only 1 to 2%. Connery and Cover (45, 47) have examined the vibrating D M E and concluded that for many analytical applications it is superior to the classical DME. They also examined some aspects of the theory of the vibrating DATE (48). Kowalski (116), and Roffia and Vianello (187) have described hanging mercury drop electrode assemblies for which the mercury reservoir can be filled without reinoving the capillary from the test solution. Solid electrode systems also have been studied extensively during the past two years. Hartley and iixelrod (87) investigated the boron carbide electrode, but in general seem to find little to recommend it. Curran and Fletcher (62) have evaluated lanthanum hexaboride as an electrode material. Their studies were performed in water where a restricted useful potential range was observed. This electrode also appears to have no important advantages over other common electrodes. Lindquist (124) has described a carbon paste electrode and electrode assembly that is said t o provide simple preparation of electrode surfaces (provided you have a lathe in the lab). He tested the system by oxidation of hydroquinone and reported peak current reproducibility of 0.27% and half-peak potential reproducibility of 1 mV. Adsorption of organic molecules by the organic phase of a carbon paste electrode has been investigated by Meier and Chambers (161). Pungor and Szepesvary (178, 179) have described an electrode consisting of graphite which is cold vulcanized with silicone rubber. Although the useful potential range is restricted, they reported excellent reproducibility of current-voltage curves. The electrode is said to require no pretreatment and the surface can be cleaned or renewed easily. Tubular graphite electrodes have been studied by Sharma and Dutt (197-199). They experimentally evaluated the hydrodynamic equation for these electrodes, and also determined the heterogeneous kinetic

parameterb for reduction of silver, Klatt and Blaedel (110) have derived the hydrodynamic equations for the catalytic regeneration mechanism; their theory was verified experimentally with the iron(II1)-hydrogen peroxide system a t a tubular gold electrode. Cooke and Graves (46) have described an electrode consisting of a thermistor connected to a platinum electrode in a micro-dewar. They were able to record currentvoltage and differential temperaturevoltage curves simultaneously. Thin-layer cells and electrode systems possess enough unique features to justify the difficulties of fabricating them. The theory and some analytical and mechanistic applications of thinlayer cells have been reviewed by Reilley (183). Hubbard (94) has published equations for the response of thin-layer electrodes to linear potential scan. Several different kinetically controlled electrode reaction schemes were considered, and the equations were found to be simpler than corresponding equations for thick-layer voltammetry. Applications of some of this theory are contained in a paper by Cushing and Hubbard (53) who investigated the oxidation mechanism of some platinum(11) complexes. Most thin-layer work has been performed with platinum, or mercury coated platinum electrodes, which has some obvious limitations. This problem apparently can be avoided with the cell assembly described by Hubbard and Anson (95). Their cell consists of solution trapped in a thin layer between a glass window with a small pinhole and a mercury electrode. Since no platinum support is required for the electrode, the full hydrogen overvoltage associated with mercury electrodes is obtained. Strohl and Polutanovich (209) have found that a packed bed of graphite granules behaves like a thin-layer cell. Bamberger and Strohl (8) evaluated analytical applications of the same cell with constant current electrolysis. I n the past two years there have been numerous studies based on electrode systems that permit simultaneous optical and electrochemical measurements. For example, Osa and Kuwana (167) have evaluated tin oxide and thin-film gold and platinum electrodes with rapid scanning spectrophotometry. Their work was concerned primarily with the behavior of these electrodes in nonaqueous solvents, a number of which were investigated. Tin oxide electrodes also are the subject of a detailed study by Strojek and Kuwana ( g 1 1 ) . They evaluated the stability and potential range, as well as the double-layer and semiconductor capacitance associated with tin oxide electrodes. The electrodes were used for simultaneous oxidation and transmission spectral measurements of ferrocyanide and p-nmino-


135 R

phenol for which there is a succeeding chemical reaction. A study of the catalytic regeneration mechanism with tin oxide electrodes was reported by Winograd, Blount, and Kuwana (230). They derived theoretical expressions for light absorbance of the electrode reaction product as a function of rate constants and potential step electrolysis. Their theory was tested by the oxidation of ferrocyanide in the presence of ascorbic acid. Kuwana and Strojek ( l a g ) , and Strojek (210) used simultaneous optical measurements to investigate the mechanism of oxidation o-tolidine. Internal reflection measurements with gold-film electrodes have been described by Prostak, hIark, and Hansen (177). They employed both controlled potential and controlled current perturbations in their investigation. Tallant and Evans (216) have used internal reflection to identify intermediates in the reduction of several carbonyl compounds in dimethylsulfoxide. Harisen (86) has described the use of thin-layer tin oxide electrodes with internal reflection measurements to study the electrode-solution interface. Srinivasan and Kuwana (207) have discussed some of the difficulties of using transparent electrodes for internal reflection spectroscopy. Winograd and Kuwana (251) have discussed in detail the source of changes in absorbance that are observed in the visible region by internal reflection with transparent electrodes. They considered both nonfaradaic and faradaic conditions, the latter case including the catalytic regeneration mechanism. A cell-electrode system suitable for both spectroscopic measurements and thin-layer voltammetry has been described and evaluated by Yildiz, Kissinger, and Reilley (232). Heineman, Burnett, and Murray (89) have described a cell consisting of multiple gold minigrids sandwiched between sodium chloride plates. With this cell they were able to perform thin-layer electrochemical measurements with simultaneous transmission optical measurements in the infrared. Photopolarography. Berg ( 1 4 ) has reviewed three current theories of t h e origin of photocurrents, and also suggested some experiments t h a t may help decide between them. Rotenberg, Gurevich, and Pleskov (188) also discussed the theory of photocurrents, and derived an expression for photocurrent as a function of electrode potential. Pleskov and Rotenberg (176) studied photocurrents experimentally and found they obeyed the Gurevich equation, even in dilute solutions of electrolyte, provided double-layer corrections are made. Korshunov, Zolotovitskii, and Benderskii (112) irradiated mercury with short light pulses and measured photocurrents as a function of potential 136R

0

and wavelength. They also found the Gurevich equation is obeyed and used it to estimate the electron work function for mercury. Imai and Yamashita (98) irradiated a D h l E in the presence of nitrate, and observed a square root dependence on nitrate concentration in agreement with Barker’s theory. The same authors (99) also used photopolarography to study the reduction of dissolved oxygen. They investigated t’he influence of surfactants, and suggested t’hat t’he effect may be due to changes in the electron work function as a result of surface coverage and to scavenging of solvated elect’rons by adsorbed molecules. Crow and Aggarwal (51) recorded photopolarograms in the presence of some nickel(I1) complexes, and made the interest’ing observation that sha.rp increases in photocurrent occur a t wavelengths essentially identical to absorption maxima in the UV-visible spectrum of the complexes. They suggested this may indicate that low-lying orbitals in t,he complex must be vacated for electron transfer to t’he complex to take place during polarographic electrolysis. An interesting experimental procedure for measuring very small photocurrents has been described by de Levie and Kreuser (54). They chop the irradiating light beam and then use synchronous rectification of the resulting ac photocurrent. They were able to measure phot’ocurrents several orders of magnitude smaller than the simultaneously flowing double-layer charging current. The phot’ocurrent sensitivity of the instrument is about A. They report’ed several experimental applications of the instrument, and discussed t,heir result’s in terms of several possible t,heoretical models. Miscellaneous. The determination of noble metals by electroanalytical methods including polarography has been reviewed by Beamish (11). Mark (IS?‘), who has studied extensively the mechanism of the catalytic waves associated with reduction of certain metal complexes, has reviewed the analytical applications of this interesting phenomenon. He cited numerous example analyses, including trace analysis of organic amines and determination of halogens and pseudo halogens. Calusaru (58) has described a novel polarographic procedure for determining the isotopic composition of wat’er. The method is based on an apparent deuterium isotope effect on bhe kinet’ics of catalytic hydrogen discharge waves. Precision is said to be of the order of 1 to 3%. Piccardi and Guidelli (173) described an experiment similar to pulse polarography, but based on a unique cell and electrode assembly. Polarographic-like curves are recorded on drops of constant area and under conditions where depletion effects are


presumably small. Tenygl (218) has described an analytical method which he calls pneumatic polarography. Electrolysis is performed a t potentials sufficiently negative or positive that hydrogen or oxygen is evolved. When another depolarizer is present, the volume of gas evolved is diminished. By measuring the difference in the volume of evolved gas between a cell with depolarizer and a reference cell containing only electrolyte, the concentration of depolarizer can be estimated. Tenygl suggested that the method should be useful for determining compounds whose half-wave potentials are close to that of hydrogen or oxygen evolution. Fujiwara et al. (76, 77) have investigated the effects of a magnetic field on polarographic currents. Although their results are interesting, the effect is very small and doesn’t appear to be of much significance. To end this review on a positive note, the paper by Christian (43) can be cited. Although not based on a very respectable statistical population, he has published data which make it appear that modern polarographers needn’t be too concerned about mercury poisoning. LITERATURE CITED

(1) Adams, R. N., “Electrochemistry at

Solid Electrodes,” Dekker, New York,

N . Y., 1969. (2) Albery, W. J., Hitchman, 11. L., Ulstrup, J., Trans. Faraday SOC.,65,

1101 (1969). (3) Albery, W. J., Ulstrup, J., Electrochim. Acta, 13,281 (1968). (4) Alimarin, I. P., -4bdel Razik, F. A., Vinogradova, E. N., Kamenev, A. I., Izv. Akad. Sauk S S S R , Ser. Khim., 1968, p 699.

( 5 ) Anson, F. C., Annu. Rev. Phys. Chem.,

19, 83 (1968). (6) Arthur, P., Rulison, D. S., Berlin, K. D., A N A L . CHCM.,40, 1389 (1968). (7) Baletskaya, L. G., Zakharova, Z. A., Zakharov, 11.S.,Izv. Akad. S a u k Kaz. S S R , Ser. Khim., 19, 34 (1969). (8) Bamberger, R. L., Strohl, J. H., ANAL.CHEM.,41, 1450 (1969). (9) Bard, A. J., Ed., “Electroanalytical Chemistry,’’ Dekker, New York, N. Y., 1969. (10) Bauer, H. H., Campbell, H. R., Shallal, A. K., J . Electroanal. Chem. Interfacial Electrochem., 21, 4.5 (1969). (11) Beamish, F. E., Anal. C h m . ,4cta, (12) 44,Belew, 263 (1969). W. L., Fisher, D. J., Jones,

H. C., Kelley, 11. T., AKLL.CHEM.,

41, 779 (1969).

(13) Benoit, R. L., Guay, >I., Ilesbarres, J., Can. J . Chem., 46, 1261 (1968). (14) Berg, H., Electrochzm. Acta, 13, 1249 (1968). (15) Berge, H., Struebing, B., Fresenius’ 2. Anal. Chem., 234, 321 (1968). (16) Ibid., 247, 12 (1969). (17) Bewick, A,, Electrochim. Acta, 13, 825 (1968). (18) Bewick, A., Thirsk, H. R., Mod. Aspects Elw-Chem., 1969, p 291. (19) Beyerlein, F. H., Nicholson, R . S., A x \L. CHEM.,40, 286 (1968). (20) Bezman, R., McKinney, T. S., ibid., 41, 1560 (1969).

(21) Bildstein, H., Fleischer, H., Gutmann, V., Znorg. Chim. Acta, 2, 347 (1968). (22) Birke, R. L., J . Electroanal. Chem. Interfacial Electrochem., 22, 319 (1969). (23) Birke, R. L., hlarzluff, W. F., ibid., 17, 1 (1968). (24) Bos, P., van Dalen, E., ibid., p 21. (25) Bowman, J. T., Bard, A. J., Anal. Lett., 1, 533 (1968). (26) Bravo, O., Iwamoto, R. T., J . Electroanal. Chem. Interfacial Electrochem., 23, 419 (1969). (27) Breant, hl., Bazouin, M., Buisson, C., Dupin, &I., Rebattu, J. M.,Bull. SOC.Chim. Fr., 1968, p 5065. (28) Breant, hI., Demange-Guerin, G., ibid., 1969, p 2935. (29) Breslow, R., Balasubramanian, K., J . Amer. Chem. SOC.,91, 5182 (1969). (30) Britz, D., Bauer, H. H., J . Electrcanal. Chem. Interfacial Electrochem., 18, 1 (1968).

(31) Broadbank, R. W. C., Dhabanandana, S., hlorcom, K. W., Muju, B. L., Trans. Faraday SOC.,64, 3311 (1968). (32) Brown. 0. R.. Electrochim. Acta. 13. 317 (1968). (33) Brown, E. Ii., Hung, 11. L., hiecord, T. G., Smith, D. E., Booman, G. L., AKAL.CHEM.,40, 1424 (1968). (34) Brown, E. R., Smith, I). E., Booman, G.L., ibid., p 1411. (35) Bruckenstein, S., Napp, D. T., J . Amer. Chem. Soc., 90, 6303 (1968). (36) Breyer, B., Pure A p p l . Chem., 15, 313 11967). (37) Burrows, B., Jasinski, R., J . Electrochem. SOC.,115, 365 (1968). (38) Calusaru, A., Rev. Chim. Mincr., 5, 387 (1968). (39) Campbell, G. hl., J . Phys. Chem., 73, 350 1969). (40; Carsky, P., Zuman, P., Collect. Czech. Chem. Commun., 34,497 1969). (41) Caselli, 32., Ottombrini, G., Papoff, P., Electrochim. Acta, 13, 241 (1968). (42) Christian, G. D., J . Electroanal. Chcm. Interfacial Electrochem., 23, 1 (1969). (43) Christian, G. D., ibid., p 172. (44) Coetzee, J. F., Simon, J. ll., Bertozzi, It. J., ANAL. CHEM.,41, 766 (1969). (45) Connery, J. G., Cover, R. E., ibid., p 1191. (46) Cooke, S. L., Graves, B. B., Chem. Instrum.. 1. 119 11968). (47) Cover, 8 . E.,’Connery, J. G., ANAL. CHEM.,41, 918 (1969). (48) Zbid.,p 1797. (49; Creason, S. C., Xelson, It. F., J . I

,

(63) Dryhurst, G., Rosen, M., Elving, P. J., Anal. Chim. Acta, 42, 143 (1968). (64) Duda, J. L., Vrentas, J. S., J . Phys. Chem., 72,1187 (1968). (65) Zbid., p 1193. (66) Feldberg, S.W., Electroanal. Chem., 3. 199 11969). (67j Filinovskii, V. Y., Elektrokhimiya, 5, 635 (1969). (68) .Filinovskii, V. Y., Podgaetskii, E. hf., zbzd., 4,671 (1968). (69) Fischer, O., Dracka, O., SteninaJakovleva. J. V.. Collect. Czech. Chcm. Commun.,’33, 2370 (1968). (70) Fischerova, E., Dracka, O., Meloun, AI., ibid., p 473. (71) Fisher, D. J., Chem. Instrum., 2, 1 (1969). (72) Fisher, D. J., Belew, W. L., Kelley, hl. T., ibid., 1, 181 (1968). (73) Fleischmann. ?viLI.. Hiddleston.’ J. N.. J . Sci. Instrum.: 1968. a 667. (74) Forcier, G. A., Oh&, J. W., Electrochim. Acta, 14, 135 (1969). (75) Forno, A. E. J., Chem. Ind. (London), 1968, p 1728. (76) Fujiwara, S., Haraguchi, H., Umezawa. Y.. ANAL.CHEM..40. 249 11968). (77) ,Fujiwara, S., Umezawa, Y . ,Kugo, T:, zhzd..n 2186. - ~ - (78) Galus, Z., Kemula, W., Sacha, S., J . Polarogr. Soc., 14, 59 (1968). (79) Gelb, R. I., J . Elcctroanal. Chem. Interfacial Electrochem., 19, 215 (1968). (80) Goudeau, J. C., Berthon, G., Camps, M.,Bernard, hl. L., Electrochim. Acta, 13. 309 - - 11968’i. (81) Gutmann, V., Duschek, O., Monafsh. Chem., 100, 1047 (1969). (82) Gutmann, V., Kogelnig, M., Michlm a y , Xi., ibid., 99, 693 (1968). 183) Zbzd.. a 699. (84) Zbid.; 707. (85) Hale, J. lI.,J . Phys. Chcna., 73, 3196 (1969). (86) Hansen, W. N., in “Proceedings of the Symposium on Modern Aspects of Reflectance Spectroscopy, Chicago, 1967,” W.W.Wendlandt, Ed., Plenum Pres., New York, N. Y., 1968. (87) Hartley, A. AI., Axelrod, H. D., ~

, I

-.

\ - - -

J . Electroanal. Chem. Znterfactal Electrochem., 18, 115 (1968). (88) Hartley, il. AI., Hiebert, A. G., Cox, J. A., zbid., 17, 81 (1968). (89) Heineman, 77’. R., Burnett, J. N., Murray, R. W., ASYL.CHI:iv., 40, 1974

New

11968). (90) Herman, H. B., Bard, A. J., J . Electrochem. Soc., 115, 1028 (1968). (91) Hevrovskv, J., Zuman, P., “Practical Polardgraphi, An Introduction for Chemistry Students,” A4cademicPress, New York, N. Y., 1968. (92) Holub, K., Nemec, L., J . Elcctroanal. Chem. Interfacial Eltctrochem., 18, 209

CHIorr;feld, D. I., Evans, D. H., ibid., 20. 341 11969). (61) ’Doronin, A. N., Elektrokhzniiya, 4, 1193 (1068). (62) Uracka, O., Collect. Czech. Chena. Commun., 34, 2627 (1969).

(93) Hrabankova, E., Dolezal, J., Chem. Listy, 62, 1164 (1968). (94) Hubbard, A. T., J . EIectroanal. Chena. Interfacial Eltctrochem., 22, 165 11969). (9.I., Nadjo, L., Saveant, J. LI., Electrochim. dcta, 13, 721 (1968). (140) RIastragost’ino, M., Saveant, J . AI., ibid.,p 751. (141) liat,suda, K., Tamamushi, R.,Bull. Chent. SOC.J a p . , 42, 439 (1969). 1142) Mazzenga, A , , Lomnitz, I)., Villeges, J., Polowczyk, C. J., Tetrahedron Lett., 1969, p 1666. (143) McCord, T. G., Hung, H. L., Smith, I

.

~

I). E., J . Erectroanal. Chem. Interfacial Electrochem., 21, 5 (1969). (144) IIcCord, T. G., Smith, D. E., ANAL.CHEM.,40, 289 (1968). (143) Ibid., p 1959.


137 R

(146) Ibid., p 1967. (147) Ibid., 41, 116 (1969). (1481 Ibid.. D 131. ?149\ Ibid.: b 1423. (15Oj McIniyre, J. D. E., Peck, W. F., ibid., p 1713. (151) Rleier, E. P., Chambers, J. Q . , ibid., p 914. (152) Miller, B., J . Elcctrochem. SOC.,116, 1117 (1969). (153) Mizuike, A., Miwa, T., Oki, S., Anal. Chim. Acta, 44, 425 (1969). (154) hlomoki, K., Ogawa, H., Sato, H., A N . ~ LCHEM., . 41, 1826 (1969). (155) Mueller, T. R., Chem. Instrum., 1, 113 (1968). (156) Mueller, T. R., Jones, H. C., ibid., 2, 65 (1969). (157) hlyers, R. L., Shain, I., ANAL. CHEM.,41,980 (1969). (158) Kekrasov, L. K.,Korsun, A. D., Elektrokhimiya, 4, 489 (1968). (159) Xelson, R. F., J . Electroanal. Chem. Interfacial Electrochem., 18, 329 (1968). (160) Nesterov, P., Korovin, K. V., Elektrokhimiya, 4, 89 (1968). (161) Oldham, K. B., ANAL. CHEM.,41, 936 (1969). (162) Ibzd., p 1904. (163) Oldham, K. B., Smith, D. E., ibid., 40, 1360 (1968). (164) Olmstead, 11.L., Hamilton, R. G., Nicholson, 11. S., ibid., 41, 260 (1969). (165) Olmstead, &I.L., Nicholson, R. S., J . Phys. Chem., 72, 1650 (1968). (166) Olmstead, M.L., Nicholson, R. S., ANAL.CHEW,41, 862 (1969). (167) Osa, T., Kuwana, T., J . Electroanal. Chem. Interfacial Electrochem., 22, 389 (1969I. \----,

(168) Palecek, E., in “Progress in Nucleic Acid Research and RIolecular Biology,” J. N. Davidson, W. E., Cohn, Ed., Academic Press, New York, N. Y., 1969, p 31. (169) Patterson, A,, Annu. Rev. Phys. Chem., 20,91 (1969). (170) Perone, S. P., Harrar, J. E., Stephens, F. B., Anderson, R. E., -4NAL. CHEM., 40, 899 (1968). (171) Perone, S. P., Jones, D. O., Gutknecht, W. F., ibid., 41, 1154 (1969). (172) Peters, D. G., Kinjo, A., ibid., p 1806. (173) Piccardi, G., Guidelli, R., Anal. Lett., 1, 771 (1968). (174) Piljac, I., Iwamoto, R. T., J .

Electroanal. Chem. Interfacial Ekctrochem., 23,484 (1969). (175) Pilla, A. A., Roe, R. B., Herrmann, C. C., J . Electrochem. SOC.,116, 1105

(1969). (176) Pleskov, Y. V., Rotenberg, Z. A., J . Electroanal. Chem. Interfacial Electrochem., 20, l(1969).

138R

0

(177) Prostak, A,, Mark, H. B., Hansen, W. N.. J . Phus. Chem.. 72. 2576 (1968). (178) Pungor, E., Szepesvky, E., Anal. Chim. Acta, 43, 289 (1968). (179) Pungor, E., Saepesvary, E., Havas, J., Anal. Lett., 1, 213 (1968). (180) Ramaley, L., Krause, M. S., ANAL. CHEM.,41, 1362 (1969). (181) Randles, J. E. B., Whitehouse, D. R., Trans. Faraday SOC.,64, 1376 (1968). 1182) Reid, D. S., Vincent, C. A,, J . Electroanal. Chem. Interfacial Electrochem., 18,427 (1968). (183) Reilley, C. N., Rev. Pure A p p l . Chem., 18, 137 (1968). (184) Robbins, G. D., Enke, C. G., J .

Electioanal. Chem. Interfacial Electrochem., 23,343 (1969). (185) Rodgers, R. S., Meites, L., ibid., 16, 1 (1968). (186) Roffia, S., Lavacchielli, hI., ibid., 22, 117 (1969).

(187) Roffia, S., Vianello, E., ibid., 23, App 9 (1969). (188) Rotenberg, Z. A., Gurevich, Y. Y., Pleskov, Y. V., Elektiokhimzya, 4, 1086 (1968). (189) Ruzic, I., Branica, RI., J . Electroanal. Chem. Interfacial Electrochem., 22,

243 (1969). (190) Ibid., p 422. (191) Salikhdzhanova, R. >I. F., Zhdanov, S. I., Zavod. Lab., 34, 6 (1968). (192) Saveant, J. M.,Rev. Chim. Miner., 5 , 477 (1968). (193) Scarano, E., Forina, >I., Bonicelli, R.1. G., RIioscu, XI., J . Electroanal. Chem. Interfacial Electrochem., 2 1, 279 (1969). (194) Schroeder, R. R., Shain, I., Chem. Instmm., 1, 233 (1969). (195) Scrosati, B., Pecci, G., Pistoia, G., J . Electrochem. SOC.,115, 506 (1968). (196) Seth, R. L., Naqvi, S. ll., Trans. SOC.Advan. Electrochem. Scz. Technol.,

3, 28 (1968). (197) Sharma, L. R., Dutt, J., Indian J . Chem., 6, 593 (1968). (198) Ibid., p 597. (199) Ibid., 7, 485 (1969). (200) Sherman, E. O., Olson, D. C., ANAL. CHEM.,40, 1174 (1968). (201) Shuman, h l . S., ibid., 41, 142 (1969). (202) Shuman, RI. S., Shain, I., ibid., p 1818. (203) Smith, T., J . Colloid Interface Sci., 30, 183 (1969). (2041 Smith. D. E.. R‘IcCord. T. G.. ‘ A 4 . 4 ~C . H ~ Y 40, . , 474 (1968). ’ (205) Smoler, I., Collect. Czech. Chem. Commun., 33, 3036 (1968). (206) Sonner, R. H., Miller, B., Visco, R. E., ANAL.CHEM.,41, 1498 (1969).


(207) Srinivasan, V. S., Kuwana, T., J . Phvs. Chem., 72, 1144 (1968). (208) Stephens, F. .B., Harrar, J. E., Chem. Instrum., 1, 169 (1968). (209) Strohl, J. H., Polutanovich, T. A., Anal. Lett., 2, 423 (1969). (210) Strojek, J. W., Zesz. Nauk. Politech. Slask., Chem., 1969, p 5 . (211) Strojek, J. W., Kuwana, T., J . Electroanal. Chem. Interfacial Electrochem., 16,471 (1968). (212) Stromberg, A. G., Baletskaya, L. G., Elektrokhimiya, 5 , 20 (1969). (213) Stromberg, A. G., Kaplin, A. A., Kuleshov, V. I., Karbainov, Y. A., Spirin, E. K., Kon’kova, A. V., Tr. Kom. Anal. Khim., Akad. -V‘auk SSSR, Inst. Geokhim. Anal. Khim., 16, 108 (1968). (214) Sturrock, P. E., Anstine, W. D., Gibson, R. H., ANAL. CHEM.,40, 505

(1968). (215) Stutter, E., Elektrokhimiya, 4, 151 (1968). (216) Tallant, D. R., Evans, D. H., A N A L . CHEY., 41, 835 (1969). (217) Taylor, D. F., Barradas, R. G.,

J . Electroanal. Chem. InteTfacial Electrochem., 23, 166 (1969). (218) Tenygl, J., Collect. Czech. Chem. Commun., 33, 4141 (1968). (219) Texier, P., Badoz-Lambling, J., Bull. Soc. Chim. Fr., 1968, p 1273. (220) Thomas, W. E., Schaap, W. B., ANAL.CHEM.,41, 136 (1969). (221) Tindall, G. W., Bruckenstein, S., ibid.,40, 1402 (1968). (222) Tindall, G . W., Bruckenstein, S., J . Elccfroanal. Chem. Interfacial Electrochem., 22,367 (1969). (223) Tommila, E., Belinskij, I., Suomen Kemistilehti B, 42, 185 (1969). (224) Tsuji, K., Elving, P. J., ANAL. CHCM..41.216 11969). (225) Tur’yan, Y: I., Elektrokhimiya, 5 , 8 (1969). (226) Tvrzicka, E., Dolezal, J., Chem. Listu, 63, 538 (1969). (227) Ulstrup, J., Electrochim. Acta, 13,

1717 (1968). (228) Verdier, E. T., Piro, J., Ann. Chim. (Paris),4, 213 (1969). 1229) Yoloshin. A. G., Elektrokhimiva. 4. 441 (1968). (230) Winograd, N., Blount, H. N., Kuwana, T., J . Phys. Chem., 73, 3456 (1969). (231) Winograd, N., Kuwana, T., J . I

,

I

Electroanal. Cham. Interjacial Electro-

c h m . , 23, 333 (1969). (232) Pildiz, A,, Kissinger, P. T., Reilley, C. N.,ANAL.CHEM.,40, 1018 (1968). (233) Zambonin, P. G., ibid., 41, 868 (1969).

Polarographic theory, instrumentation, and methodology

Recommend Documents