121440h (1973). (336) Songina, 0. A,, Zakharov, V. A,, Usp. Anal. Khim., 1974, 273, (Ed., Zolotov, Yu. A,, Petrikova, M. N., "Nauka": Moscow, USSR); Chem. Abstr., 82, 1 6 4 3 7 4 ~ (1975). (337) Songina, 0. A,, Zakharov, V. A,. Bekturova, G. B., Lopukhova, I. P., Zavod. Lab., 39, 920 (1973); Chem. Abstr., 80, 22290y (1974). (338) Songina, 0. A., Zakharov, V. A,, Bekturova, G. B., Smirnova, L. I., Zh. Anal. Khim., 29, 1594 (1974); Chem. Abstr., 82, 38164n (1975). (339) Sontag. G., Kainz, G., Margaritella. P., Fresenius' Z. Anal. Chem., 273, 263 (1975); Chem. Abstr., 83, 21565s (1975). (340) Stahlavska. A., Vydra, F., Bartova. M., Slansky, V., Cesk. Farm., 22, 212 (1973); Chem. Abstr.. 79, 97054n (1973). (341) Stamovs, S.,Dimitrova, V., Lipchinski, A,. Genov, I., God. Vissh. Khim.-Tekhnol. lnst., Burgas. Bulg., 10, 451 (1973); Chem. Abstr., 83, 71030j (1975). (342) Stock, J. T., Microchem. J., 16, 557 (1971). (343) Stock, J. T., Anal. Chem., 46, 1R (1974). (344) Strojek, J., Uziel, Z.,Zak, J., Chem. Anal. (Warsaw), 19, 185 (1974); Chem. Abstr., 81, 67905q (1974). (345) Strukova, M. P., Veslova, G. I., Provoius, L. I., Zh. Anal. Khim., 30, 383 (1975); Chem. Abstr., 83, 22052j (1975). (346) Sukhoruchkina, A. S.. Postnikov. V. A,, Usatenko, Yu. I., Zavod. Lab., 39, 917 (1973); Chem. Abstr., 80, 222912 (1974). (347) Sukhoruchkina. A. S.,Usatenko, Yu. I., Pozina. L. I., Gorizontova, T. N., Vopr. Khim. Khim. Tekhnol., 32, 44 (1974); Chem. Abstr., 82, 678022 (1975). (348) Suprunovich, V. I., Usatenko, Yu. I., Velichko, V. V., Ukr. Khim. Zh. (Russ. Ed.), 39, 488 (1973); Chem. Abstr., 79, 132576h (1974). (349) Suprunovich, V. I., Usatenko, Yu. I., Yamnova, T. P., Vopr. Khim. Khim. Tekhnol., 34, 18 (1974); Chem. Abstr., 83, 71005e (1975). (350) Suzuki, S., Bunseki Kagaku, 23, 426 (1974); Chem. Abstr., 81, 204019 (1974). (351) Suzuki, H., Yang, H-C., Dempun Kagaku, 20 (2), 59 (1973); Chem. Abstr., 83, 117552m (1975). (352) Takahashi, M., Yoshida, Y., Aoyagi, H., Izawa, K., Mikrochim. Acta, 1974, 329; Chem. Abstr., 81, 9365c (1974). (353) Takahashi, T., Nomura, E., Yamamoto, O., Denki Kagaku, 41, 127 (1973); Chem. Abstr., 80, 534312 (1974). (354) Tarasyants, R. R . , Streietskaya, E. N., Kuleshova, 0. D., Bondarevskaya, E. A,, Zh. Anal. Khim., 29, 1398 (1974); Anal. Abstr., 29, 3856 (1975). (355) Tarayan, V. M., Acharayan, G. S., Shaposhnikova. G. N., Arm. Khim. Zh., 27, 279 (1974); Chem. Abstr., 81, 85590n (1974). (356) Tarayan, V. M., Shaposhnikova, G. N., Acharayan, G. S.,ibid., p 350; Chem. Abstr., 81, 85574k (1974). (357) Tolk. A., Anal. Chem. Nucl. Fuels, Proc.
Panel, 1970(pub. 1972), p 1. (358) Toropova, V. F., Degtyareva, V. N., lzv. Vyssh. Ucheb. Zaved., Khim. Khim. Tekhnol. 17, 175 (1974); Chem. Abstr., 80, 152439q (1974). (359) Toropova, V. F., Degtyareva, V. N., Biktagirova, A. A,, Zh. Anal. Khim., 29, 757 (1974); Chem. Abstr., 81, 57933h (1974). (360) Trinko. A. I., Sirakanyan, M. A,. Agasyan, P. K., Bobroserdova, N. B.. Gostunskaya, I. V., Vestn. Mosk. Univ., Khim.. 15, 333 (1974); Chem. Abstr., 81, 1630479 (1974. (361) Tsayun, G. P., Yudovich. E. E., Khim. Tekhnol. Topl. Masel, 1974 (6), 55; Chem. Abstr., 81, 96092c (1974). (362) Tserkovnitskaya. I. A,, Dubrovina, L. T., Vestn. Leningrad. Univ., Fiz., Khim., 1973 (4), 128; Chem. Abstr., 80, 103460f (1974). (363) Tulyupa, F. M.. Usatenko, Yu. I., Sharonina. R. M., Shvydka, L. F., Barkalov, V. S.,Pavlichenko, V. A,, Tkacheva, L. M., Fiz.-Khim. Metody Anal. Kontr. Proizvod., Mater. Konf. Rab. Vuzov (Vyssh. Uch. Zaved.) Zavod. Lab. Yugo-Vostoka SSSR, 4th, I , 87 (1971); Chem. Abstr., 80, 1156428 (1974). (364) Unterman, H. W., Weisbuch. S..Pharmazie, 29, 752 (1974); Anal. Abstr., 29, 1E21 (1975). (365) Usatenko, Yu. I., Galushko. S. V., Zavod. Lab., 41, 270 (1975); Chem. Abstr., 83, 125652j (1975). (366) Usatenko, Yu. I., Sitaio, L. I., ibid., 39, 784 (1973); Chem. Abstr., 80, 33528h (1974). (367) Usatenko. Yu. I., Sitalo, L. I., Zh. Anal. Khim., 29, 35 (1974); Chem. Abstr., 80, 127846n (1974). (368) Usatenko, Yu. I., Suprunovich, V. I., Velichko, V. V.. ibid., p 807; Chem. Abstr., 81, 578504 (1974). (369) Usatenko. Yu. I., Suprunovich, V. I., Yamnova. T. P.. Zavod. Lab., 39, 1175 (1973); Chem. Abstr.. 80, 555259 (1974). (370) Usvyatsov, A. A,, Sudakov, A. R.,Krylov, Yu. A., Agasyan, P. K., Zh. Anal. Khim., 29, 170 (1974); Chem. Abstr., 80, 1279151 (1974). (371) Vajgand. V. J., Pastor, T. J.. Glas. Hem. Drus., Beograd, 37, 499 (1972); Chem. Abstr., 80, 103629t (1974). (372) Vajgand, V. J., Pastor, T. J., Bjelica. L. J., Mikrochim. Acta, 1975, 485; Chem. Abstr., 83, 125858f (1975). (373) Van Acker, P.. De Corte, F., Joste, J., Anal. Chim. Acta, 67, 236 (1973). (374) Vandegans, J., Merciny, E., Duyckaerts, G., ibid., 72, 391 (1974). (375) Vandenbalick, J. L., Mairesse-Ducarmois. C. A,, Patriarche, G. J., J. Pharm. Belg., 29, 361 (1974); Chem. Abstr., 82, 25481p (1975). (376) Vartanyan, S. V., Tarayan, V. M., Arm. Khim. Zh., 27, 469 (1974); Chem. Abstr., 81, 130505b (1974). (377) Vartanyan, S. V., Tarayan. V. M., Zavod. Lab., 41, 15 (1975); Chem. Abstr., 83, 37105c (1975). (378) Vikharev, B. G., Basov, V. N., Gidroiiz. Lesokhim. Prom., 1974 (2), 6; Chem. Abstr., 81,
93270y (1974). (379) Vitovec, V., Sb. Pr. Vyzk. Chem. Vyuziti Uhli. Dehtu Ropy, 13, 169 (1973); Chem. Abstr., 83, 21369f (1975). (380) Vshivtsev. A. D., Karnaukh, S. I., Khim. Seraorg. Soedin., Soderzh. Neft. Nefteprod,. 9, 456 (1972); Chem. Abstr., 79, 1425202 (1973). (381) Vucurovic, B. D., Javanovic. M. S..G l k . Hem. Drus., Beograd, 39, 301 (1974); Chem. Abstr., 83, 22047m (1975). (382) Westcott, C. C., Beckman lnstrum., lnc., Tech. Rep., 1974, 548. (383) Yakovlev, P. P.. Nichugovskii, G. F., Zozulya, A. P., Zh. Anal. Khim., 28, 2061 (1973); Chem. Abstr., 80, 91007v (1974). (384) Yamasaki, S., Ohura, H., Nakemori, I., Bunseki Kagaku, 22, 843 (1973); Chem. Abstr., 80, 77941s (1974). (385) Yoshida, Z.,Aoyagi. H., Takahashi, M., ibid., 23, 374 (1974); Chem. Abstr., 81, 4 4 8 8 8 ~ (1974). (386) Yoshimori. T., ibid., p 1431; Chem. Abstr., 82, 79917d (1975). (387) Yoshimori, T., Sakaguchi, N., Talanta, 22, 233 (1975). (388) Yoshimori, T., Tanaka, T., ibid., p 33. (389) Yoshimori, T., Tanaka. T.. Anal. Chim. Acta, 66, 85 (1973). (390) Yoshimori, T., Umezaki, S.,Tanaka, Y., Bunseki Kagaku, 21, 1381 (1972); Chem. Abstr., 78, 52147h (1973). (391) Yurow, H. W.. Sass, S., Anal. Chim. Acta, 56, 297 (197 1). (392) Zakharov, V. A,, Aitkhozheva, T. A,, Zavod. Lab., 41, 164 (1975); Chem. Abstr., 83, 52807b (1975). (393) Zakharov, V. A., Songina, 0. A,, Aitkhozeva, T. A,, Zh. Anal. Khim., 29, 1130 (1974); Chem. Abstr., 81, 130543n (1974). (394) Zakharov, V. A,, Songina, 0. A,, Bessarabova, I. M., Toibaev, E. I., Sb. Rab. Khim., Kaz. Univ., 1973, No. 3, 198; Chem. Abstr., 81, 180890~ (1974). (395) Zakharov. V. A,. Tokusheva, G. T., ibid., p 206; Chem. Abstr., 81, 145241m (1974). (396) Zanello, P.. Cospito, M., J. Eiectroanai. Chem. Interfacial Electrochem., 52, 133 (1974). (396a) Zauls, L., Veiss, A,. Latv. PSR Zinat. Akad. Vestis, Kim. Ser. 1973, 687; Chem. Abstr., 80, 90982a (1974). (397) Zhdanov, A. K., Akhmedov, G., Nauch. Tr., Tashkent Univ., 1972, No. 419, 43; Chem. Abstr., 79, 121541s (1973). (398) Zhdanov, A. K.. Barkhudar'yan, A. A,, Uzb. Khim. Zh., 18 (5), 15 (1974); Chem. Abstr., 82, 105949n (1975). (399) Zhdanov, A. K.. Markhabaev, I. A,, izv. Vyssh. Ucheb. Zaved., Khim. Khim. Tekhnol., 16, 1331 (1973); Chem. Abstr., 80, 22315k (1974). (400) Zhdanov, A. K., Markhabaev, I. A,, Muminov. N. P., Uzb. Khim. Zh. 18 (4), 15 (1974); Chem. Abstr., 82, 381892 (1975). (401) Zhdanov, A. K., Muminov, N. P., Zh. Anal. Khim., 29, 1424 (1974); Chem. Abstr., 82, 25403q (1975).
.
Analytical Electrochemistry: Theory and Instrumentation of Dynamic Techniques David K. Roe* and Pascal Eggimann Department of Chemistry, Portland State University, Portland, Ore. 97207
This review follows the same plan as the previous one under this title (18A);the period covered is from December 1973 to December 1975. Publications on the theory of electrode processes have been divided into sections according t o emphasis: mass transport, charge transfer, surface effects, homogeneous reactions, and instrumentation. The
section on noise has been dropped because of low signal level. Most papers fall clearly into one of these sections, although there is a trend toward broad coverage. In such cases, either some mention was made of the additional topics or a second citation in the appropriate section was added. Again, the aim was to prepare an overview which ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1976
9R
would complement the current version of the review by Kissinger (13A)on methodology and application.
BOOKS AND REVIEWS A text emphasizing the experimental aspects of electrochemistry is also useful for its introduction to theory (IOA). The second volume of “Techniques of Electrochemistry” appeared early in this review period (21A). An annual review of electrochemistry for 1973 includes a survey of voltammetry ( 8 A ) .The 1974 volume (20A) is of general interest, covering selected topics from the literature through 1972. A volume in the Faraday Discussions was devoted to intermediates in electrochemical reactions; the introductory comments by Gerischer ( 9 A ) set a challenging pace for these contributions. Pletcher (17A) reviewed the study of homogeneous reactions by controlled potential techniques, but ac methods were not included. General, but brief, reviews on methods for the study of electrode processes ( l l A ) , and theory of charge transfer a t electrodes ( 6 A ) were prepared by acknowledged experts. Direct methods for study of intermediates and products in electrode reactions often rely on a spectroscopic technique; a review edited by R. H. Muller (15A) includes all current methods with chapters by Hansen, Kruger, Muller, McIntyre, Simon, and Srinivason. Applications of faradaic reactification were reviewed by Agarwal ( I A ) ,and classical polarography was treated thoroughly in a comprehensive chapter by Fisher ( 7 A ) . Square wave polarography was summarized with applications (19A).Three volumes in the series edited by Bockris and Conway (3A-5A) contain many topics, including double layer electrocatalysis, absorption, and hydrogen electrode studies. The distinction between the symmetry factor and transfer coefficient was stressed by Bockris ( 2 A ) .Official recommendations for nomenclature (16A),and sign conventions as well as plotting of electrochemical data (12A)have been made. Anyone who enjoys speculating about complex interfacial processes will find abundant material in the new electrochemical-mechanical oscillators described recently (14A). They involve mercury, of course, like the classic beating heart demonstration.
MASS TRANSPORT I t is unlikely that this topic will reach, in the near future, a state of completion with no need for innovations. There are so many possible geometries of electrodes and means for enhancing transport of. reacting species to interfaces that Fisk’s laws of diffusion, augmented in various forms, will continue to be the most frequently solved partial differential equations in science. Most electrochemical methods easily qualify for analytical applications in terms of precision, which requires highly reproducible mass transfer. (An example which lacks precision in the hands of many experimentalists is chronopotentiometry in which it is difficult to identify a characteristic state in mass transfer. In spite of many attempts to overcome this problem, the technique finds very few devotees.) Presently, the trend is toward greater rigor in the description of mass transfer so that absolute errors can be decreased. This is an essential requirement if electrochemical methods are to achieve reliability in the study of homogeneous reactions; if you disagree or find this surprising, talk to, anyone who uses stop-flow techniques to study homogeneous reaction rates ( 8 B ) . Most contributions along these lines will be found in the section on homogeneous reactions. Many experimentalists have been led to believe that a rotating disk electrode must be accurately centered on the axis of rotation. Surprisingly, an eccentricity of 0.6 leads to an enhancement of the limiting current by only 1%but rises sharply with increasing eccentricity, according to Mohr and Newman (21B)who also verified their prediction with copper deposition experiments. Of course, the electrode holder must rotate without eccentricity to keep the solution in the cell. These results should give confidence to do-it-yourselfers. Extreme eccentricity leads to a small electrode in the end of a large rotating rod, and a little imagination reveals that this is similar to a stationary electrode in a laminar flow stream. If two small rectangular 10R
ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1976
electrodes are separated by a thin insulator and oriented normal to the stream lines, then reaction products can be investigated ( 7 B ) as with ring-disk electrodes or the same arrangement in a flow stream (31B).Interestingly, the collection efficiency is zero if the direction of rotation is reversed. Occasions where it may be experimentally necessary to monitor two products from a disk electrode led to analog (lOB, 11B) and digital solutions (19B) of collection efficiencies of double-ring electrodes; no immediate advantage over the split-ring arrangement is apparent. Pulse polarography a t rotated electrodes requires mass transfer equations that span the gap between the Cottrell and the Levich equations. An approximate equation for transient responses has been modified and found to apply over a wide range of rotation rates and pulse times (22B). Transient convective diffusion in the limiting current region has received additional attention in the region of both short (24B)and long (25B)times relative to rotational convection. Solutions of ac impedance of rotating disk electrodes have been derived by several methods (13B, 17B) and compared (18B). The nonuniformity of current distributions on a rotating disk electrode when operated a t currents below the limiting value has been recognized for a few years. In a complementary manner, the current distribution on a rotating sphere is uniform below 68% of the limiting value, but becomes nonuniform above this point (23B). Turbulent flow a t hemispherical electrodes has been added to the list of theoretical treatments of this geometry by Chin (6B). Flow-through electrodes of various geometries, tubular, porous (bundle of tubes), and thin layer, have possibilities in analysis, synthesis, and power generation. The idea is to achieve a form of dynamic coulometry. Many assumptions have been necessary in past, analytic solutions; a test of the range of applicability of these approximations has been made by digital simulation ( 9 B ) of a tubular electrode. Transient responses under both controlled potential and controlled current conditions were also examined. Validity of the bundle-of-tubes model for a porous electrode has been shown (32B) when radial diffusion is included. Vibrationally-induced mass transfer is not new, but theoretical treatments of this mode are very unusual because of the complexities of the motion, e.g., vibrating DME. A system amenable to mathematical analysis has been devised and th‘e average current expression derived by dimensional analysis (27B).The simplicity of the arrangementa conventional loudspeaker provided the longitudinal vibrations-and the high, relative efficiency suggest that this technique should not be overlooked. Where else is there the possibility of correlation analysis with Ravel’s Bolero as an input signal? Anodic stripping voltammetry is sensitive but time-consuming; hence the increasing use of pulse and ac methods. Osteryoung and Christie (26B) have provided theoretical treatments of pulse stripping from thin mercury film electrodes a t two levels of complexity: redeposition of the metals ions between pulses and consideration of diffusional losses. Since peak currents are nearly the same under normal pulse conditions as they are under linear potential scan, the advantage is the significant decrease in background current. Similar benefits accrue from the use of an ac signal superimposed on a linear potential scan with phase selective, second-harmonic detection (5B). An impressive number of publications have appeared in the Russian chemical literature on anodic stripping from thin mercury films. Representative citations are: ac stripping ( 4 B ) ; rotating mercury film electrode ( 1 B ) ;stripping chronopotentiometry ( 2 B ) ; influence of excessive concentration of one metal on another a t low concentrations (14B);effect of stirring (16B). Ruzic and Smith (28B)have launched a rieorous reexamination of the effects of e’lectrode curvature i“n ac polarography. When the products form amalgams, the errors caused by neglect of sphericity are startling-up to 50% in i,. Digital simulation is an appropriate method for handling the added complexities due to sphericity according to Ruzic and Feldberg (29B),who showed that the expanding sphere model could be added to existing digital simulation programs. Spherical effects were included (12B) in the treatment of the semi-integral methods to explain the slight
Davld K. Roe is associate professor at Portland State University, Portland, Ore. He received his A.B. degree from Pacific Lutheran University in 1954, the S.M. degree from Washington State University in 1956, and the Ph.D. degree from the University of Illinois in 1959. After a postdoctoral year in Stuttgart, Germany, he was with the Corrosion Department of Shell Development, Emeryvilie, Calif., for two years and then was an assistant professor in the Chemistry Department at MIT and associate professor at the Oregon Graduate Center. His research interests are in electrochemistry and its analytical applications and in electronic instrument design.
Pascal Egglmann studied chemistry at the Ecole Polytechnique Federale of Lausanne (Switzerland) and then at the lnstitut de Chimie minerale et analytique where he received the Ph.D. degree in 1975. His major interests are in the study of surface effects, general instrumentation and optimization methods. He is presently Research Associate at Portland State University.
slope found in neopolarograms measured with a hanging mercury drop electrode. A clever nosepiece was devised to eliminate shielding by the glass capillary and to allow strictly spherical geometry. Model refinements which decrease computation time or improve accuracy in digital simulation have been described in adjacent publications. In the first, Sandifer and Buck (30B) noted that placing the electrode in the middle of the first volume element and using a second derivative, finite difference approximation could result in a hundredfold decrease in computer time in some cases, compared to the method originally described by Feldberg. Joslin and Pletcher ( 1 5 B ) were primarily concerned with simulation of potential step experiments where there is a following catalytic reaction. Their improvement involves a variable space grid so that rapid homogeneous kinetics may be simulated without the excessive computation time required by a fine, uniform space grid (see also the section of homogeneous reactions). Barker ( 3 B ) extended his views of equivalent circuits to include large signals which do not allow linear approximations. The visual representation requires a non-uniform resistive transmission line. Inclusion of successive electron transfer steps results in the addition of a transformer element with turns ratio given by the ratio of the number of electrons in the two steps. Calculation of diffusion coefficients by comparing currents at planes and spherical electrodes was suggested some years ago. Combining results of a number of voltammetric techniques leads in a similar manner to experimental diffusion coefficients, net number of electrons transferred, and transfer coefficients (20B).
CHARGE TRANSFER In the early publications on semi-integral (or convolution) methods, the applicability to the study of rate of charge transfer was shown. Two clear advantages were apparent: true potentiostatic conditions were not required and an a priori assumption of a rate equation was not essential to interpretation. Interest in exploiting these advantages is increasing and certain problems, mainly capacitive charging current, have been recognized and partially solved. Potential scan methods have been employed by Saveant and co-workers and they (13C) have been successful at rates of 100 V/s. A very convenient technique for the extraction of charge transfer rate constants from potential scan data is to use both the current and its semi-integral
(27C).The equations allow straightforward calculations. A clever method of obtaining Ell2 was also revealed, and this is an essential parameter in the calculation. An example with high solution resistance where the iR drop exceeded 1 V has been described (31C). A very valid point was made that the potentiostat is not needed-only a signal generator. Charging currents must be absent from the current values prior to semi-integration, and the usual technique is to subtract a residual run (13C, 27C, 3 I C ) under the same conditions. Potential step methods with semi-integration can be very easily applied to charge transfer kinetic studies (3C, 26C). There is no need to restrict the step size, so that the potential dependence of rate constants can be examined easily. Rodgers (26C) developed a very direct set of equations which yielded a linear relation between m ( t ) , the semi-integral, and i ( t ) .A slope-intercept analysis permits calculation of rate constants. He also suggested that charging current corrections can be made with a short current pulse, provided one knows the double-layer capacitance. I t seems he preferred this wave form because of experimental convenience. Although the semi-integral was evaluated digitally, the convenience of an X-Y display of i ( t )vs. an analog semi-integration to give m ( t ) was said to be in the offing. Further refinements of these methods are anticipated and they should be very versatile. We have been led to think that very rapid charge transfer reactions can only be studied by decreasing the time scale of the measurement and/or increasing the precision so that mass transport limiting may be avoided and/or accounted for. Some successful examples of high precision in ac polarography have been published (4C, 9C) as well as square wave ( 6 C ) relaxation on the 10-ns time scale. With characteristic elan, Fleischmann and co-workers ( 2 C ) have demonstrated, in theory and experiment, that other means exist to cut through the mass transport barrier. At a spherical electrode, flux is dependent upon D/a, where D is the diffusion coefficient and a is the radius. By working with radii of the order of 10 nm, mass transport control is forestalled to the seconds-time region so that rather leisurely measurements can be used even when the apparent heterogeneous rate is very large (up to 100 cm/s). Since such a small radius implies inconveniently small currents, they arranged to have about lo6 spheres. The final form of the experiment is a vitreous carbon electrode plunged into a mercury pool counter electrode, thereby trapping a thin film of solution. Instantaneous, independent, and uniform nucleation of mercury is assumed, but not verified. Of course the method was used with the Hg22f 2e- = 2Hg reaction only, but a little ingenuity should allow several other systems to be studied. Since the theory allowed large potential steps, it was possible to test the potential dependence of the rate constant and transfer coefficient. The interpretation was made without accurate values of 42 potentials, but showed reasonable agreement with the Marcus prediction of a dependence upon the square of the overpotential. In a more conventional system, Ayabe ( I C ) used the currenttime curve of a dropping mercury electrode to obtain kinetic data. In a series of papers (14C-17C), Rangarajan has extended his unified view of electrochemical relaxation methods to a unified approach for formalizing nearly all aspects of chemistry at electrified interfaces. His formalism was based upon selected, linear system parameters which allowed direct development of equations for a wide variety of mechanisms and relaxation techniques. Faradaic-nonfaradaic coupling is said to be a natural and expected event as viewed through his formalism. Nonlinearity of electrochemical systems, as observed in faradaic rectification and demodulations was addressed in a second series (18C-20C) and also in the first ( 2 I C ) of a third group on high amplitude techniques with the intent of again providing a unified approach. Mathematical complexities arise in profusion, but Rangarajan provides many parenthetical comments to guide and inform the reader. These generalities, which include many mechanistic schemes, help to sharpen intuition and the next step might be to guide the experimentalist towards the shortest and most reliable path in mechanistic studies. Schuhmann (30C) has shown how a variety of reaction schemes may be analyzed with high am-
+
ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1976
* 11 R
plitude signals through a change of variables that in turn allows conventional transform methods to be used. Faradaic rectification resulting from an amplitude modulated sine wave was analyzed (32C) and found to contain information about both high- and low-frequency properties of an electrode. Nonlinear excitation signals promise certain characteristics for use in kinetic studies of charge transfer. Theory (14E, 20C) and one experimental study (22C) have appeared for time-dependent, controlled current imputs. No decisive clarification of the wide range of reported rate constants resulted from applying this novel technique to the hexacyanoiron(I1)-(111) reaction (22C). Impedance spectra covering a wide frequency range have been suggested (7C) as a powerful means to unravel reaction mechanisms, but very high precision is necessary when characteristic time constants differ by less than 1:lOO (5C). Surprisingly, there are still significant details to be learned about conventional polarographic current-voltage curves. Ruzic (24‘2) pointed and that with quasi-reversible waves, the factor (7/3)lI2 should not be used over the entire potential range since diffusion control becomes less im or tant as the potential becomes more negative. The res& is that the slope of log (& - i) vs. potential is not constant and not equal to LY nF/RT. Also the slope is not the same when mean or peak currents are used. When consecutive electron transfers occur with chemical reactions, the slopes of these plots are variable depending upon relative rates and transfer coefficients. It was alse shown (25C) that in some cases, individual values for transfer coefficients could be obtained. Attempts to measure a potential dependence of the transfer coefficient have not been conclusive because the reactions used had too high a rate constant, according to Klatt and Lewis (11C). They calculated current-potential curves for various reaction rates with and without a POtential-dependent transfer coefficient and concluded the difference becomes measurable if k < 2 X cm/s. The factor (7/3)’/*was included in their calculations, however. Improvements on the dielectric continuum model of Levich and Dogonadze were made by Schnickler and Vielstich (29C),who also suggested that an inaccurate treatment of the solvent organization before and after electron transfer has been overlooked. They predicted from consideration of dielectric relaxation times of the primary hydration sheath that quantum effects should be apparent a t room temperature, instead of only a t low temperatures. Khristov ( 2 0 C ) described a general formulation of electron transfer processes which includes the probability of nuclear tunneling as well. Occasionally, quantum mechanical methods are focused upon an isolated system to the point of calculation of rate constants. Lai and Hubbard (12C) have shown some success in this direction for reactions proceeding through a bridging ligand. The concept of stoichiometric numbers has been reviewed (8C, 23C) and applications discussed. Two approximations concerning electronic states in the electrode are that electron transfer occurs only at the Fermi level and that this is a step function. An exact treatment (28C) reveals that the first approximation is valid a t low overpotentials (Marcus theory) and the second holds over a wide range, but especially at high overpotentials (Hale’s modification).
SURFACE EFFECTS A decade or so in the past, the majority of publications directed towards interfacial phenomena were concerned with double layer capacity or one of its many details. Gradually, charge transfer kinetics and that elusive transfer coefficient required for their interpretation more structural and energetic details of the interfacial region; it was a reciprocal relation, of course, and the theory of the double layer was refined in turn. The papers cited in this section reflect an increasing proportion of interest in the role of the electrode surface, adsorption of reactants and products, and the influence of the inner Helmholtz plane on charge transfer processes. The kinetics of charge transfer involving specifically adsorbed reactants have been shown ( 2 3 0 ) to follow a modified Tafel equation which includes the potential dependence of the activity of the reactant (and product if it is 12R
ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1976
also specifically adsorbed). No isotherm was assumed; indeed it can be experimentally determined through the equations of the model. Weaver and Anson ( 2 4 0 ) also suggested that inner and outer sphere electrode mechanisms could be distinguished through the change in rate caused by the presence of a strongly adsorbed but weakly complexing anion-a demanding requirement-but iodide ion was found to qualify in the case of Cr(II1)-complex ions. Site competition decreased the rate of the inner sphere reaction paths, while enhancement of the rate through electrostatic effects results with the other type. Examples studied verified the criteria, qualitatively but convincingly. A similar type of anion-induced adsorption of a reactant cation was described within the context of diffusion controlled, cyclic voltammetry ( 1 7 0 ) . Asymmetry of the cathodic and anodic currents was predicted when a potentialdependent isotherm was included in the numerically calculated curves; several examples with bromide ion were studied and interpreted semi-quantitatively. Ionic species undergoing charge transfer a t the inner Helmholtz plane are subject to lateral coulombic attractions and self-image potentials. In the theories which attempt to take these factors into account, the variation of the dielectric constant is important, but difficult to include because of mathematical complexities and because it is not known in any detail. The charge transfer coefficient is the thermometer of such effects and its variation with potential was calculated with refined models ( 4 0 , 1 4 0 ) . Rather large potential ranges (-200-500 mV) were required to produce large changes in Tafel slopes. A comparison of several approaches to describe such reactions has also been published ( 8 0 ) . Prewaves and postwaves reported by Brdicka have been generally treated by Laviron (120-130) for polarography and linear scan voltammetry. Equations for current-potential curves were obtained for low coverage (Langmuir isotherm) for Nernstian and irreversible conditions as well when the product undergoes an irreversible chemical reaction. Several types of isotherms were examined to fit experimental curves at high coverage. Interaction between adsorbed molecules, as expressed by the Frumkin isotherm, permitted the curves to be sharp peaks (high attractive forces) or broad curves (repulsion dominates). Pseudo-prewaves were predicted when the product is strongly adsorbed and inhibits the reaction. Many other details were included in the discussion. A second-order adsorption reaction preceding charge transfer was theoretically distinguishable from a first-order adsorption under certain limiting conditions ( I D ) .The adsorption process of interest involves hydrogen molecules; it would seem to be more direct to identify this case as first-order adsorption followed by dissociation. Adsorbed intermediates interposed between two charge transfer steps have been theoretically analyzed for ac impedance ( 2 0 ) . Complex plane plots were used to identify the details of the model. If the intermediate inhibits the first electron transfer, the impedance will have a negative real part and oscillations are possible, depending upon the damping. A variety of electrochemical mechanisms, including adsorption, were interpreted on this basis ( 1 8 0 , 2 0 0 ) and a number of oscillators were demonstrated ( 1 0 0 ) . Adsorption accompanied by “partial charge transfer” was first suggested by W. Lorenz and Pleith in an attempt to quantify a detail in electrochemistry on a microscopic basis. Vetter and Schultze introduced a similar concept but termed it the “electrosorption valency”: it included a charge term involving a reactant and also other changes in the double-layer structure. Terminology problems arose as well as some confusion about the development of these concepts in the framework of current double-layer theory. Recently, it was suggested that the model of “electrosorption valency” required nonthermodynamic assumptions ( 5 0 ) in the absence of a supporting electrolyte, for example, and that the term “formal coefficient of charge transfer” would be more appropriate. The original term was defended ( 2 2 0 ) , the concept was clarified somewhat, and then was extended to mixed adsorption. After this polemical exchange, Frumkin et al. ( 6 0 )provided a careful comparison of the three terms, showed their interrelations, and the physical meaning in terms of the extent of the view-mi-
croscopic or macroscopic. On the basis of this comparison, it is not surprising that partial charge transfer could not be measured kinetically ( 2 3 0 ) . Future difficulties with terminology can be expected since a similar situation was defined with regard to monolayer deposition of metals and the term “charge coverage coefficient” was coined ( 1 5 0 ) . Underpotential deposition of metals is a phenomenon without a general theory. Symmetrical behavior was shown to occur a t slow scan rates in cyclic voltammetry ( 7 0 ) .The amount deposited and removed amounted to about one half of an equivalent monolayer. Interestingly, the difference between peak potential under these conditions and the standard potential for the deposited metal ion-metal couple was correlated with the difference in work function of the deposited metal and the substrate metal. The proportionality between these two differences was constant for a large number of systems studied with two solvents. Another insight into underpotential deposition was provided by an analysis of ring and disk currents during linear potential scans ( 2 1 0 ) .Assuming that sequential deposition of two metals is independent when both are a t less-thanequivalent monolayer coverages, it was shown that isopotential points (same current for different amounts deposited) would result a t both the ring and disk electrodes as the less-noble metal was oxidized. It is a little obscure when described so briefly, but the conclusion was that the two metals were deposited a t independent regions of the disk. It would be very interesting to choose the two metals on the basis of differences in work functions and compare with the previous observations ( 7 0 ) . The recent symposium on electrocatalysis includes many papers of significance in the area of surface effects. Particular mention should be made of combined ESCA-electrochemical studies by Winograd ( 2 5 0 ) and the successful incorporation of a cell into a vacuum system by Hubbard ( 9 0 ) so that electron scattering studies could be performed with minimum contamination. An improvement in the model used to calculate the capacitance of the inner layer was suggested by Damaskin and Frumkin ( 3 0 ) .It involved clusters as well as individual chemisorbed water molecules. Parsons ( 1 6 0 ) improved upon this idea by accounting for the total number of molecules in the inner layer and assuming the dipole moment OF a cluster was the same as that of a single molecule. According to an analysis by Scheider (19D), surface roughness is responsible for variations of interfacial capacity with frequency in many experimental situations in which adsorption (impurity or otherwise) was assigned the causal role. While his conclusions are correct for real, solid surfaces, exculpation of adsorption processes does not follow. HOMOGENEOUS REACTIONS Electrode processes involving chemical reactions have been modeled mathematically with increasing rigor over the past 20 years. Significant improvements are evident in two areas in the literature of this review. First, the use of approximations to make the equations tractable has given way to combined analytic-digital simulation methods or rigorous analytic solutions were obtained first and then simplified. Second, there is increasing awareness that the range of possible models has been incomplete and that additional reactions and their rates (the “nuances” noticed by Feldberg about 10 years ago) must be considered. Two improvements ( 1 5 4 30B) in the accuracy-computation time tradeoff were noted in the section on mass transport. Both were shown to advantage in simulation of cataB, B A) under potonlytic following reactions (A e tial step conditions. An additional refinement is the use of an implicit solution (27E) along with digital simulation on a variable space grid (15B). Ruzic and Feldberg (20E)have shown that the problem of fast homogeneous re‘actions, which require hours of computer time, can be solved by reducing the reactions scheme to an equivalent system involving only a single heterogeneous step. This slight-ofhand transformation was accomplished by solving the differential equations for the short-lived intermediate, using a steady-state approximation a t the electrode surface, and then introducing this explicit result in a normal digital simulation of the time-space solution of the other species. The
+
- -
method worked for preceding and following reactions, but the range of validity of the steady state approximation has not been defined. A hybrid computer would be useful in extending this approach to more complicated mechanisms. Of all electrochemical techniques, ac polarography has received the greatest attention in the study of coupled homogeneous reactions. I t is now highly sophisticated in instrumentation, at least in one laboratory, so that experimental data warrant rigorous theories. Also the range of systems to which it can be applied requires that theoretical limitations in terms of, e.g., minimum rate constants and reaction orders, must not impede its use. For example, the old steady-state approximation has gradually been eliminated; one more case, charge transfer followed by an irreversible first-order reaction, has been theoretically treated (19E) without this assumption. The rigorous results were reduced in complexity for ease of calculation of rate constants with. little sacrifice in accuracy. Pseudo first-order conditions cannot be imposed on dimerization and disproportionation reactions following charge transfer, so this complexity has forestalled rigorous solutions. A nearly rigorous treatment (steady state was invoked) for fundamental ac polarography response in the presence of disproportionation (JOE)and irreversible dimerization ( I I E ) was based upon a collection of mathematical strategies. Several electrode geometries were used, including the expanding sphere. Both publications include thorough discussions of some unusual predictions that provide a basis for identification of these mechanisms relative to first-order reactions. Diagnostic criteria for preceding first-order chemical reactions ( 4 E ) and for catalytic reactions ( 5 E ) have also been developed for fundamental and second harmonic ac polarography. No limitations on rates of reactions were imposed. At the next level, two independent charge transfers coupled with a homogeneous redox reaction were attacked and solutions applicable to both ac and dc polarography were presented (21E, 25E). Essentially no restrictions on the system were imposed in terms of homogeneous and heterogeneous rates, diffusion coefficients, and electrode geometry. A similar situation arises with consecutive charge transfer reactions since the intermediate is involved in a redox reaction with the final product and initial reactant. This case was treated in a similar manner (22E). The wellknown ECE mechanism did not escape and again both ac and dc polarographic response were presented (23E). All three of these mechanisms were handled by digital simulation of the dc boundary value problem and the small amplitude, analytic ac solution was obtained subsequently using the surface concentration components from the dc solution. Elegant! Elimination of the reaction layer concept from dc polarographic theory produces final equations that are difficult to apply to experiment. The recent approach has been to develop working curves or simplified equations of tested reliabilit,y. Matsuda (17E) has completed this task for the average current-potential curves (not just average limiting current) for CE, EC, and ECE mechanisms under Nernstian conditions. With Nishihara, he (18E) provided similar results for limiting currents a t the expanding plane for CE and catalytic currents. Single- and double-potential step methods occupy second place in theoretical developments during this review period. An analytic solution for first-order disproportionation was obtained ( 7 E ) , although a numerical solution was available. Based upon the steady-state approximations, analytic solutions ( 3 E ) were developed for two variations on catalytic currents: the products of the chemical step are the initial reactant and a species which reacts further with the product of the charge transfer reaction or is reduced directly. While the current-time curves are different enough to be diagnostically useful, experimental results were not clearly interpreted. Previous equations for potential step chronoabsorptometry applied to one absorbing species. Li and Wilson (16E) expanded the list of mechanisms to a total of ten and very thoughtfully included the absorbancetime relation for all species. When analytic methods failed, they resorted to digitally simulated curves. Some years ago, the Osteryoungs made a strong pitch for the advantages of chronocoulometry over chronamperometry. Lawson and Maloy (15E) now claim that the half-way ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1976
13R
point, chronoamplometry is more accurate and diagnostically useful in the study of EC, ECE, and second-order dimerization mechanisms. They employed a double potential-step. Analog semiintegration was also suggested as the preferred method for data processing. Prompted by the realization that heterogeneous oxidation of organic compounds favors products from the least stable intermediate while homogeneous oxidation (normal organic synthesis) leads to products from the least stable reactant, Fleischmann e t al. (8E) developed a variation on the double potential-step technique to examine the details of the chemical reactions of intermediates. Two independent electrode reactions are involved in this scheme and the first step causes both to occur. By proper selection of the second step, the current-time curve reflects a flux balance in the case where the product of one reaction reacts with the more easily oxidized reactant. Working curves were prepared by digital simulation to determine reaction rates and some mechanistic variations. Linear potential scans are widely used because of the firm and extensive theoretical base developed over the past decade. Convolution of the current-time data with a digital computer (or semiintegration) effectively removes the diffusional component of the signal and reveals the influence of homogeneous reactions. The case of a first-order following reaction has been treated (24E)and references were made to application involving dimerization. Cyclization mechanisms become very involved when other chemical steps are possible after charge transfer. Linear sweep, rotation disk, and classical polarographic methods were applied ( I E ) to 15 different cases to provide a range of diagnostic criteria. Nonlinear perturbation functions have not received much attention in the study of homogeneous reactions. They were introduced in chronopotentiometry by Reilley and implemented by Murray for diffusion-controlled charge transfer reactions. Rangarajan (20C) extended the idea to include charge transfer kinetics, also noted in the last review. Recently, the application was made to EC and catalytic mechanisms, using power-of-time and exponential-in-time inputs ( 1 4 E ) . Analytic solutions resulted from Laplace transfer methods. While preselected, nonlinear input signals may prove to be powerful diagnostic techniques, it would seem that another approach has equal merit. That would be to preselect the time variation of the output signal and derive the necessary form of the input signal. I t might prove to be easier for complex mechanisms. Concentration impedance a t a rotating disk electrode in the presence of an EC mechanism was developed numerically (17B). The ECE mechanism with porous electrodes was examined from the view point of selectivity of products (26E). Intermediates that produce ESR signals and that are involved in homogeneous reactions are amenable to a kinetic analysis through digitally developed working curves ( 9 E ) .A current pulse was the input signal. Cyclic chronopotentiometry was advocated (6E) as a critical technique to kinetically analyze ECE and disproportionation reactions. Digitally developed curves show that the third transition time is able to distinguish between these two mechanisms. A second-order chemical reaction preceding charge transfer was theoretically treated for ac chronopotentiometry ( 2 E ) .Formation of complex with metal ions during anodic stripping was analyzed so that stability constants and reactions rates might be assessed (12E, 13E).
INSTRUMENTATION Before summarizing the advancements in electrochemical instrumentation, a reasonable prediction of future directions might be suggested by identifying the state-of-theart of electronic components. Clearly, the most significant recent development is the integrated circuit microprocessor, now widely available a t low cost. Along with low cost IC memories and data converters, it opens the door to the design of “smart instruments” which are capable of closedloop control of data acquisition and reduction. Instruments built around a microprocessor replace the combination of a “dedicated” lab computer interfaced to a normal instrument. The result is improved user convenience with no sacrifice in performance. Cost savings are impressive, as can 14R
ANALYTICAL CHEMISTRY, VOL. 48, NO.
5, APRIL 1976
be seen by comparing the 1968 price of the Princeton Applied Research Model 170 with the current price of the microprocessor-oriented Model 374. Many other examples of smart instruments have appeared in the last year, including chromatographs, oscilloscopes, and spectrum analyzers. Two introductory articles (12F, I3F) will help one to understand the impact that these devices will have in future. Digital logic based upon the CMOS gate is now available in a wide variety logic functions a t a price competitive with T T L logic, but with the advantages of low power drain, usable with a wide range of supply voltages and high noise immunity. Several linear devices are available in CMOS and the simple inverter can be used as a limited purpose op amp. The CA 3130 (RCA) op amp has a MOS input stage and is very fast, but noise and thermal drift are not impressive. A better choice is the LF356 (National) which can replace man discrete op amps a t a fraction of the price. Only a $w new details on the application of minicomputers to electrochemistry have appeared, although it is not uncommon to read comments on their use. Interfacing a number of different types of lab instruments involves several problems, such as the need for different data sampling rates. An application (32F)using 16 on-line instruments showed how to overcome such problems a t minimum commitment of memory. Another example of on-line use of a computer in ac polarography involved enhancement of signal-to-noise ratio through averaging a number of measurements (16F). A general discussion on the use of computers in solving complex electrode mechanisms was prepared (9F). Function generators for the control of input parameters have typically been composed of analog components. Digital control of voltage limits, holding periods, slopes, and integration regions are relatively easy to implement, although the approaches differ widely. One group published simultaneously circuits for both a digitally controlled analog function generator (integrator output) (42F) and for a digital output version (39F)using a 16-bit digital-to-analog converter. The latter has the additional feature of partial control through the keyboard of a programmable calculator. A DAC output is of course a staircase, but when the steps are only 30 wV, it is essentially a continuous function and also has negligible drift. A similar device was developed with a 10-bit DAG (31F).Programmable holding voltages and times are the features of another circuit (15F);similar results can also be obtained by the multisegment synthesis route ( I I F ) . Another function generator-potentiostat was designed with digital control of all functions so that compatibility with a computer or microprocessor was possible (35F). Among several approaches to the attainment of true potentiostatic conditions, the automation of a positive feedback loop has reached a respectable state of development. I t should be noted that iR compensation by positive feedback was used by Hodgkin, Huxley, and Katz in their classic work published in 1952; this reference is usually overlooked. Techniques for two- and three-electrode cells were described based upon a small square wave input and automatic gain adjustment in the positive feedback loop (48F, 49F). The first method (48F) works well with slow scans, reaching full compensation in about 0.1 s while the second (49F) is about a hundred times faster. Very few details were given on maintaining loop stability. An interesting variation on the interrupter method was shown to be capable of very high correction rates ( 8 F ) . The controller amplifier, or potentiostat was made into a short time constant integrator by placing a 10-nF capacitor between output and inverting input. At the moment that the output-to-auxiliary electrode connection was opened, the sum of the cell potential (from a voltage follower) plus input signal was applied to the inverting input and integrated. This set the potentiostat output to the necessary level to compensate for iR drop in the cell. The switching occurred rapidly so that the level of compensation could be updated in about 50 ws. A manually set, but very fast and stable method of iR compensation was briefly suggested (17F)and then thoroughly analyzed (29F). I t was based on making the current-to-voltage converter into a negative impedance device. Simply connecting the noninverting input to a voltage divider from the output accomplishes this; the inverting
input terminal is no longer a t virtual ground, but moves away from the input signal. The main advantage is that the positive feedback loop involves only one amplifier and therefore only one pole, so loop stability is easy to ensure. Strangely enough, the first article (17F) used a resistor in series with the potentiostat output to measure the current, and the second article (29F) failed to mention that this form of current-to-voltage converter has an output voltage that is not simply proportional to the product of cell current and feedback resistor, but instead depends upon the degree of compensation. The focus was iR compensation only. I t is easy to achieve both compensation and measurement of cell current through the use of a subtractor circuit between the output and the voltage applied to the noninverting input. But first some inherent problems of currentto-voltage converters must be considered in potentiostat circuits, as outlined by Davis and Toren (IOF). In the ring-disk electrode situation, the problems of iR drop are complicated by the differing current densities. A method of expressing the problem (37F) was proposed, but no attempt was made to completely eliminate resistance effects because of the nonuniform currents (38F). Two improved pulse polarographic circuits were described as having low noise (44F) and new modes of operation to improve detection limits (26F, 44F). A universal voltammetric instrument was assembled so that several type of voltammetric measurements could be selected (45F). Some details were given concerning the conversion of the widely-used Heathkit polarograph to solid state op amps; only the case and panel controls were used from the original device ( I F ) . Bandwidth limitations in linear scan voltammetry result in peak enhancement. An analysis of this distortion and a clever diagnostic technique were proposed (18F). When operating near the maximum usable scan rate, the addition of a resistor between the potentiostat output and auxiliary electrode will reduce loop gain and therefore also reduce the upper frequency limit. If the current peak increases, the safe range has been exceeded. Instead of observing current-potential curves in linear scan methods, an analog computer was used to convert the signal to show the change of surface concentration (36F)with potential. Some advantages accrue when multiple waves occur. Integrator circuits have benefited from digital logic control. Two forms allow new degrees of operation in terms of on-off periods and reset (3F, 41F) and another was designed for peak integration in polarography (25F).Integrator errors were analyzed with regard to major sources of drift and a chopper stabilized circuit was added to bring the total errors to less than 0.1% without the need for frequent manual adjustment (46F), but some external timing device was required. Another circuit was published (30F) to accomplish the same goal, but the details were unavailable a t the time this review was written. Both integrators were intended for chronocoulometry, but other applicaLITERATURE CITED
Books and Reviews (1A) Agarwai, H. P., Electroanal. Chem., 7, 161-271 (1974). (2A) Bockris, J. O'M., Nagy, Z.,J. Chem. Educ., 50, 839-43 (1973). (3A) Bockris, J. O'M., Conway, B. E., "Modern Aspects of Electrochemistry", Vol. 9, Plenum Press, New York. 1974. (4A) Ref. 3A, Vol. 10, (1975). (5A) Ref. 3A, Vol. 11, (1975). (6A) Dogonadze, R. R., Kuznetsov, A. M.. Proc. Symp. Eiectrocatal., Breiter, M. W., Ed., Electrochem. SOC.,Princeton, N.J., 1974. (7A) Fisher, D. J., Adv. Anal. Chem. Instrum., 10, l(1974). (8A) Fleet. 6.. Jee, R. D., Electrochemistry, 3, l(1973). (9A) Gerischer. H., Faraday Discuss. Chem. SOC., 56 (1974). (lOA) Gileadi, E., Kirowa-Eisner, E., Penciner, J., "interfacial Electrochemistry: An Experimental Approach", Addison-Wesley, Reading, Mass., 1975 . _ (11A) Heitbaum. J., Vielstich. W., Angew. Chem., 86, 756-70 (1974).
tions in instrumentation might benefit as well. Semiintegration by analog methods was reported by Oldham in the last review period. Now semidifferential electroanalysis has been suggested and implemented by analog differentiation of the semiintegral (20F). A method for charging current compensation in polarography has been shown (34F) to extend the limits of detection to M; the method was originally suggested by Barker and involves imposing a small sine wave on the cell. Controlled current density instrumentation for an inverted form of polarography has been revised and automated (24F). A successful form of changing current compensation in chronopotentiometry has been described and used for very short transition times (40F). It is based upon the time differential of the potential, as were earlier attempts, but stability was marginal. A variation on the Howland constant current generator has been described (21F) and switching problems for galvanostats (23F)were solved. Several galvanostatic pulse methods were compared, and it was concluded that the double-pulse method was the best one, capable of giving charge transfer impedance and electrode capacitance measurements only 80 ns after the start of the pulse (14F). Impedance measurements with sine wave inputs require phase selective detection for interpretation. One version was developed by analogy with classical bridge methods ( 4 F ) ,but the final version could also be viewed as a modern ac polarograph minus the potentiostat. Distinguishing features are the frequency range, 0.005 Hz to 10 kHz, and high resolution with very high impedance cells, like glass electrodes. Correlation methods with the previously described, iR-compensationed, current-to-voltage converter were analyzed and compared to other methods (17F). Problems arising from the use of impedance measurements with overlapping current peaks were discussed (43F); kinetic measurements were reported for reactions in aprotic solvents (27F) ; and applications to trace analysis were demonstrated (33F). Second-harmonic phase selective detection can be inexpensively added to a commercial instrument by generating the second-harmonic reference signal with an electronic multiplier which squares the fundamental wave (6F).Rather rapid linear potential scans were also incorporated in the same instrument (5F). An improved controlled alternative current polarograph was described ( 7 F ) ;it featured wider range of operation than the classical "oscillographic" version. A variation on modulation polarography involved applying a 2-MHz sine wave current to the cell along with a low frequency voltage. The output is an amplitude modulated 2-MHz signal, from which the capacitive component of the cell could be obtained in the presence of solution resistance and faradaic reaction (2F). Miscellaneous instruments include those for measuring rotation rates of disk electrodes (19F,22F, 28F) and a oscillator-type mercury drop fall detector (47F).
(12A) IUPAC Committee on Electoanalyticai Chem.. IUPAC, lnC Bull., Append. Provis. Nomencl., Symb., Units, Stand., 42 (1975). (13A) Kissinger, Peter T., Anal. Chem., 46, 15R-21R (1974). (14A) Lin, S., Keizer. J., Rock, P. A,, Stenschke, H., Proc. Natl. Acad. Sci. USA, 71, 4477-81 (1974). (15A) Muller, R. H., Ed., Adw. Electrochem. Electrochem. Eng., 9, l (1973). (16A) Parsons, R., Pure Appl. Chem., 37, 499-516 (1974). (17A) Pletcher. D., Chem. SOC. Rev., 4, 471 (1975). (18A) Roe, David K., Anal. Chem., 46, 8R-15R (1974). (19A) Sturrock, P. E., Carter, R. J., Crit. Rev. Anal. Chem., 5, 201 (1975). (20A) Electrochemistry, 4, 1 (1974). (21A) Yeager, E.. Salkind, A. J., "Techniques of Electrochemistry", Vol. 2, Wiley-lnterscience, New York, 1973. Mass Transport (16) Bakanov, V. i., Zakharov, M. S . , Antip'eva, V. A., Grigorchenko, A. P., Zh. Anal. Khim., 28, 2292-7 (1973).
(28) Bakanov, V. I., Zakharov. M. S., Antip'eva, V. A., Cheremnykh, N. M., Elektrokhimiya, 11, 95-8 (1975). (38) Barker, G., J. Eiectroanal. Chem., 58, 5-18 (1975). (48) Bashkatov, V. Z., Stromberg, A. G., Zh. Anal. Khim., 28, 2101-6 (1973). (58) Blutstein, H., Bond, A. M., Anal. Chem., 46, 1531-8 (1974). (66) Chin, Der-Tau, AlChE J., 20, 245-50 (1974). (78) Despic, A. R., Mitrovic, M. V.. Nikolic, B. Z . , Cvijovic, S. D., J. Electroanal. Chem., 60, 141-9 (1975). (88) Eigen, M., private communication, 1966. (96) Flanagan. James 8.. Marcoux. Lynn, J. Phys. Chem., 78, 718-23 (1974). (106) Filinovskii, V. Yu, Kadija. I. V.. Nicolic, B. Z . , Nakic M. B., J. Electroanal. Chem., 54, 39-46 (1974). ( 1 l B ) Filinovskii, V. Yu. Kadija. I, V., Nikolic, B. Z.,Elektrokhimiya, 10, 297-300 (1974). (128) Goto. M., Oldham, K. B.. Anal. Chem., 46, 1522 (1974). (138) Homsy. Robert V., Newman, John, J. Electrochem. Soc., 121, 521-3 (1974). (148) Igoiinskii. V. A,, Gur'yanova, 0. N., €lektrokhimiya, 11, 57-61 (1975).
ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1976
15R
(158) Joslin, T., Pletcher, D., J. Electroanal. Chem.. 49, 171-86 (1974). (16B) Komarova, L. I., Elektrokhlmiya, 9, 1286-90 (1973). (17B) Levart, E., Schuhmann. D.. J. Electroana/. Chem., 53, 77-94 (1974). (18B) Levart. E., Schuhmann. D.. J. Electrochem. Soc., 122, 1082-3 (1975). (19B) Margarit, Jacques, Levy, Michele, J. Electroanal. Chem., 4g, 369-76 (1974). (208) Moeller, D., Knaack. J. D., J. Electroana/. Chem., 63, 303-9 (1975). (218) Mohr, Charles M.. Jr., Newman, John, J. Electrochem. SOC., 122, 928-31 (1975). (228) Myers, David J., Osteryoung. R. A,, Osteryoung, Janet, Anal. Chem.. 46, 2089-92 (1974). . (238) Nisancioglu, Kemal. Newman, John, J. Electrochem. SOC., 121, 241-6 (1974). (248) Nisancioglu, Kemal, Newman, John, J. Electrochem. SOC., 121, 523-7 (1974). (258) Nisancioglu, Kemal, Newman, John, J. Electroanal. Chem., 50, 23-9 (1974). (268) Osteryoung, Robert A,, Christie, Joseph H., Anal. Chem., 46, 351-5 (1974). (278) Podesta, J. J., Paus, G. F.. Arvie, A. J., Nectrochlm. Acta, 19, 583-9 (1974). (288) Ruzic, Ivica. Smith, Donald E., J. Electroanal. Chem., 57, 129-39 (1974). (298) Ruzic, Ivica, Feldberg, Stephen W.. J. Electroanal. Chem., 63, 1-7 (1975). (308) Sandifer, J. R., Buck, R . P., J. Electroana/. Chem., 49, 161-70 (1974). (318) Tokuda, Koichi, Matsuda, Hiroaki. J. Electroanal. Chem., 52, 421-31 (1974). (328) Wroblowa, Halina S., Razumney, Gerardo, J. Electroanal. Chem., 49, 355-68 (1974). Charge Transfer (1C) Ayabe, Yuzo, J. Electroanal. Chem., 55, 187-99 (1974). (2C) Bindra. P., Brown, A. P., Fleischmann. M., Pletcher, D., J. Electroanal. Chem., 58, 31-7 (1975). (3C) Carney, J. H., Miller, H. C., Anal. Chem., 45, 2175 (1973). (4c) Creason, Sam C., Smith, Donald E., Anal. Chem., 45,2401-3 (1973). (5C) Dyer, C. K., Thin Solid Films, 23, S37S40 (1974). (6C) Dyer, C. K., Leach, J. S.L., Electrochim. Acta, 19, 695-700 (1974). (7C) Goehr, Hermann, Meissner, Wilhelm, 2. Phys. Chem., 93, 217-34 (1974). (8C) Horiuti, Juro, Ann. N.Y. Acad. Sci., 213, 5-30 (1973). (9C) Hirota, Michio, Umezawa, Yoshio. Kojima, Hiroyuki, Fujiwara, Shizuo. Bull. Chem. Soc. Jpn., 47, 2486-9 (1974). (1OC) Khristov. S. G., Ber. Bunsenges. Phys. Chem., 79,357-71 (1975). (11C) Klatt, Leon N., Lewis, David R., Anal. Chem., 46, 24-9 (1974). (12C) Lai, Chiu-Nan, Hubbard, Arthur T., lnorg. Chem., 13, 1199-1204 (1974). (13C) Nadjo, L., Saveant, J. M., Tessier, D., J. Electroanal. Chem., 52, 403-12 (1974). (14C) Rangarajan, S.K., J. Electroanal. Chem., 55,297-327 (1974). (15C) Rangarajan, S. K., J. Electroanal. Chem., 55, 329-35 (1974). (16C) Rangarajan, S. K.. J. Electroanal. Chem., 55, 337-61 (i974). (17C) Rangarajan, S. K.. J. Electroanal. Chem., 55, 363-74 (1974). (18C) Rangarajan, S. K.. J. Electroanal. Chem., 56, 1-25 (1974). (19C) Rangarajan, S. K.. J. Electroanal. Chem., 56, 27-53 (1974). (2OC) Rangarajan, S. K., J. Electroanal. Chem., 62, 31-41 (1975). (21C) Rangarajan, S. K., J. Electroanal. Chem., 56, 55-71 (1974). (22C) Rao. G., Prabhakara, Lakshmanan, S., Ranoaraian, S. K., J. Electroanal. Chem., 62, 273-9 (1975). (23C) Ratner, Mark, Ann. N.Y. Acad. Sci., 213, 31-44 (1973). (24C) Ru& I., J. Electroanal Chem., 49, 407-13 (1974). (25C) Ruzic. I., J. Nectroanal. Chem., 52, 331-54 (1974). (26C) Rodgers, Robert S.. Anal. Chem., 47, 281-5 (1975).
l6R
(27c) Saveant, J. M., Tessier, D., J. Nectroana/. Chem., 65, 57 (1975). (28C) Schmickler, W., Electrochim. Acta, 20, 137-41 (1975). (29C) Schmickler, W., Vielstich, W.. Electrochlm. Acta, 10, 883-8 (1973). (30C) Schuhmann, Daniel, C. R. Hebd. Seances Acad. Sci., Ser. C, 277, 627-9 (1973). (31C) VandenBorn. H. W., Evans, Dennis H., Anal. Chem., 46, 643-6 (1974). (32C) Van der Pol, F., Sluyters-Rehbach, M., Sluyters. J. H., J. Nectroanal. Chem., 62, 281-90 (1975). Surface Effects (1D) Alquie-Redon, Anne M.,Aldaz, Antonio, Lamy, Claude, J. Electroanal. Chsm., 52, 11-25 (1974). (2D) Armstrong, R. D.. Firman, R. E., Thirsk, H. R., Faraday Discuss. Chem. SOC., 56, 244-63 (1973). (3D) Damaskin, E. B.. Frumkin, A. N., Electrochlm. Acta, 19, 173 (1974). (4D) Fawcett, W. R., J. Chem. Phys., 61, 3842-50 (1974). (5D) Frumkin, A. N., Damaskin, B. B., Petrii, 0. A,, J. Electroanal. Chem., 53, 57-65 (1974). (6D) Frumkin, A. N., Damaskin, E. B., Petrii, 0. A,, 2. Phys. Chem. (Lelpzlg), 256, 728-36 (1975). (7D) Gerischer, H., Kolb, D. M., Pazasnyski, M., Sur6 Sci., 43, 662-6 (1974). (8D) Guidelii, Rolando, J. Electroanal. Chem., 53, 205-18 (1974). (9D) Hubbard, Arthur T., Ishikawa. Roy M., Schoeffel, James A., Proc. Symp. Electrocatal., 1974, 258-67 (Pub. 1974). (10D) Jakuszewski, B., Turowska, M.. J. Electroanal. Chem., 46, 399-410 (1973). (11D) Laviron, E., J. Electroanal. Chem., 52, 355-93 (1974). (12D) Laviron. E., J. Electroanal. Chem., 52, 395-402 (1974). (13D) Laviron. E., J. Electroanal. Chem., 63, 245 (1975). (14D) Levine, S., Robinson, K., Fawcett, W. R., J. Nectroanal. Chem., 54, 237-52 (1974). (15D) Lorenz. W. J., Hermann, H. D., Wuethrich, N., Hilbert, F., J. Electrochem. SOC., 121, 1167 (1974). (16D) Parsons, Roger, J. Electroanal. Chem., 59, 229-37 (1975). (170) Quyen, N. Q., Lorenz, Wolfgang, Z. Phys. Chem. (Leipzig), 256, 33-40 (1975). (18D) Salie, Gunter, 2. Phys. Chem. (Leiprig), 253,406-10 (1973). (19D) Scheider, Walter, J, Phys. Chem., 79, 127-36 (1975). (20D) Turowska, Maria, SOC.Sci. Lodz., Acta Chim., 18, 85-98 (1974). (21D) Untereker, Darrel F., Bruckenstein, Stanley, J. Electroanal. Chem., 57, 77-87 (1974). (22D) Vetter, K. J., Schultze, J. W., J. Electroanal. Chem,, 53, 67-76 (1974). (23D) Weaver, Michael J., Anson, Fred C., J. Electroanal. Chem., 58, 61-93 (1975). (24D) Weaver, Michael J., Anson, Fred C., J. Am. Chem. SOC.,97,4403-5 (1975). (25D) Kim, K. S., Sell, C. D., Winograd, Nicholas, Proc. Symp. Electrocatal., 1974, 242-57 (Pub. 1974). Homogeneous Reactions (IE) Andrieux, C. P.. Saveant, J. M., J. Electroanal. Chem., 53, 165-86 (1974). (2E) Bansal, N. P., lndian J. Chem., 11, 1199-200 (1973). (3E) Britton, Wayne E., Fry, Albert J.. Anal. Chem., 47, 95-1 00 (1975). (4E) Bullock, Kathryn R., Smith, Donald E., Anal. Chem., 46, 1069-74 (1974). (5E) Bullock, Kathryn R., Smith, Donald E., Anal. Chem., 46, 1567-76 (1974). (6E) Cukman, D., Pravdic, V., J. Electroanal. Chem., 49,415-19 (1974). (7E) Evans, Dennis H.. Rosanske, Thomas W., Jimenez, Pedro J., J. Electroanal. Chem., 51, 449-51 (1974). (8E) Fleischmann, M., Joslin, T., Fletcher, D., Electrochim. Acta, 19, 511-17 (1974). (9E) Goldberg, Ira E., Bard, Allen J., J. Phys. Chem., 78,290-4 (1974). (10E) Hayes, John W., Ruzic, Ivica, Smith, Donald E., Booman, Glenn L., Delmastro, Joseph
ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1 9 7 6
R., J. Electroanal. Chem., 51, 245-67 (1974). (1 1E) Hayes, W., Ruzic, Ivica, Smith, Donald E., Booman, Glenn L., Delmastro, Joseph R., J. Electroanal. Chem., 51, 269-85 (1974). (12E) Karbainov, Yu. A,, Reznikova, S. S., Stromberg, A. G.. Elektrokhlmlya, 9, 1351-3 (1973). (13E) Karbainov. Yu. A,. Reznikova, S. S., Stromberg, A. G., Elektrokhimiya, I O , 1156-8 (1974). (14E) Kontturi, K., Lindstrom M., Sundholm, G., J. Electroanal. Chem., 63, 263 (1975). (15E) Lawson, R. Joe, Maloy, J. T., Anal. Chem., 46, 559-62 (1974). (16E) Li, Chia-Yu. Wilson, George S., Anal. Chem., 45,2370-80 (1973). (17E) Matsuda, Hiroaki, J. Electroanal. Chem., 56, 165-75 (1974). (18E) Nishihara. Chizuko, Matsuda, Hiroaki, J. Electroanal. Chem., 51, 287-93 (1974). (19E) Nishihara. Chizuko, Sato. Gen P.. Matsuda, Hiroaki. J. Electroanal. Chem., 63, 131-8 (1975). (20E) Ruzic, I., Feldberg, S., J. Electroanal. Chem., 50, 153-62 (1974). (21E) Ruzic, Ivica, Smith, Donald E.. Feldberg, Stephen W.. J. Electroanal. Chem., 52, 157-92 (1974). (22E) Ruzic, Ivica, Smith, Donald E., J. Electroanal. Chem., 58, 145-75 (1975). (23E) Ruzic. I., Sobel, H. R., Smith, D. E., J. Electroanal. Chem., 65, 21 (1975). (24E) Saveant, J. M., Tessier, D., J. Electroana/. Chem., 61, 251-73 (1975). (25E) Schwall. Richard J., Ruzic, Ivica, Smith, Donald E., J. Electroanal. Chem., 60, 117-23 (1975). (26E) Sioda, R. E., Electrochim. Acta, 20, 457-61 (1975). (27E) Winograd. N., J. Electroanal. Chem., 43, l(1973).
Instrumentation (1F) Andrew, R. W., Chem. Instrum., 6, 16372 (1975). (2F) Barker, G. C., Bolzan, J. A,, Gardner. A. W., J. Electroanal. Chem., 52, 193-208 (1974). (3F) Belanger, G.. Chem. Instrum., 6, 55-65 (1975). (4F) Bentz, A. M.. Sanifer, J. R., Buck, R. P., Anal. Chem., 46, 543-7 (1974). 46,(5F) 1934-41 Blutstein, (1974). H., Bond, A. M., Anal. Chem.,
(6F) Blutstein, H., Bond, A. M., Norris, A,, Anal. Chem., 46, 1754-8 (1974). (7F) Brand, M. J. D., Fleet, E., Electrochim. Acta, 19, 337-40 (1974). (8F) Britz, D., Brocke, W. A,, J. Electroanal. Chem., 58,301-11 (1975). (9F) Conway, B. E., Tilak, B. V., AngersteinKozlowska. H., Klinger, J., Comput. Chem. Res. Educ., Roc. lnt. Conf., 1, 1/67-1/97 (1973). (1OF) Davis, J. E., Toren, E. C., Jr., Anal. Chem., 46,647-50 (1974). (1 1F) Deroo, D., Forestier, M.. LeGorrec, B.. Rouveyre. J. C., C. R. Hebd. Seances Acad. Sci., Ser. C, 260, 251-4 (1975). (12F) Dessy, R. E., Janse-Van Vuuren. P., Titus, J. A., Anal. Cheni., 46, 917A (1974). (13F) Ref. 12F, p 1055A. (14F) Durand. R . , Amosse, J., Barbier, M. J., Electrochim. Acta, 19, 207-14 (1974). (15F) Farwell, S. O., Geer. R. D., Chem. lnstrum., 5, 199-213 (1973). (16F) Fujiwara, S., Hirota, M., Sawatari, K., Kojima, H., Umezawa, Y., Bull. Chem. SOC.Jpn., 47, 499-500 (1974). (17F) Gabrielli, C.. Keddam, M.. Electrochim. Acta, 19, 355-62 (1974). (18F) Garreau, U.,Saveant, J. M., J. Electroana/. Chem., 50, 1-22 (1974). (19F) Goldberg, I. B., Carpenter, R. S., 11, Goeppinger, S. F., Anal. Chem., 46, 321-22 (1974). (20F) Goto, M., Ishii, D., J. Electroanal. Chem., 61, 361-5 (1975). (21F) Grimmes, S.. Chem. lnstrum., 5, 141-4 (1973). (22F) Hahn, J., Doerfel, C., Eckert, J., Schwabe, K., Chem. Techno/., 26, 170-3 (1974). (23F) Jovic, F., Kontusic, I., J. Electroanal. Chem., 50,269-76 (1974). (24F) Kies, H. L.. Van Dam, H. C., J. Electroan-
a/. Chem., 46, 391-7 (1973). (25F) Kies, H. L., Den Os, M., Anal. Chlm. Acta. 67, 246-50 (1973). (26F) Klein, N.. Yarnitzky, C.. J. Electroanal. Chem., 61, 1-9 (1975). (27F) Kojima. H., Bard, A. J., J. Electroanal. Chem., 63, 1 17-29 (1975). (28F) Kretscmer, K. J., Hamann, C. H., Fassbender, E., J. Electroanal. Chem., 60, 231-4 (1975). (29F) Lamy, C.. Herrmann, C. C., J. Elecfroana/. Chem.. 59, 113-34 (1975). (30F) Lindstrom, M., Sundholm, G.. Finn. Chem. Lett., 27-30 (1975). (31F) Magno, F., Bontempelli, G., Mazzocchin, G. A,, Patane, I., Chem. Instrum., 6, 239-57 (1975). (32F) Overton. M. W., Alber, L. L.. Smith, D. E., Anal. Chem., 47, 363A (1975).
(33F) Poojari, A,, Rajagopalan, S. R., Rangarajan, S. K., Trans. SOC. Adv. Electrochem. Scl. Techno/.,6, 147-53 (1973). (34F) Poojary, A., Rajagopalan, S. R., J. flectroanal. Chem., 62, 51-8 (1975). (35F) Ramaiey, L., Chem. Instrum., 6 , 119 (1975). (36F) Senda, M.. Ikeda. T., Rev. Polarogr., 19, 51-5 (1973). (37F) Shabrang, M.. Bruckenstein, S., J. flectrochem. SOC.,121, 1439-44 (1974). (38F) Shabrang. M., Bruckenstein, S., J. flectrochem. SOC.,122, 1305 (1975). (39F) Sherwood, W. G., Untereker, D. F., Bruckenstein, S., Anal. Chem., 47, 84-8 (1975). (40F) Sturrock, P. E., Hughey, J. L., Vaudreuii, E., O’Brien, G. E., Gibson, R. H., J. Electrochem. SOC.,122, 1195-200 (1975). (41F) Thomas, L. C.. Christian, G. D., Daniel-
son, J . D. S . , Anal. Chim.. Acta, 77, 163-9 (1975). (42F) Untereker, D. F., Sherwood, W. G., Martincheck. G. A,, Reidhammer, T. M.. Bruckenstein, S., Chem. Instrum.,6, 259-66 (1975). (43F) Vittori, O., Porthault, M., Bull. SOC.Chlm. Fr., 11,Pt. 1. 2411-14(1974). (44F) Vassos, E. H., Osteryoung, R. A,, Chem. Instrum., 5 , 257-70 (1974). (45F) Willems, G. G.. Neeb, R., Fresenlus Z. Anal. Chem., 269, 1-10 (1974). (46F) Woodward, W. S., Ridgway, T. H., Reilley, C. N., Anal. Chem., 46, 1151-4(1974). (47F) Yarnitzky, C., J. Electroanal. Chem.. 5 1 , 207-10 (1974). (48F) Yarnitzky, C., Friedman, Y., Anal. Chem., 47,876-80 (1975). (49F) Yarnitzky, C., Klein, N.. Anal. Chem., 47, 880-4 (1975).
Analytical Electrochemistry: Methodology and Appl cat ons of Dynamic Techniques Peter T. Kissinger Department of Chemistry, Purdue University, West Lafayette, Ind. 4 7907
I t behooves us to begin this piece on a Bicentennial note, however, it was not until April of 1800 that William Nicholson and Anthony Carlisle first used Volta’s pile (1794) t o demonstrate electrochemical decomposition of water into hydrogen and oxygen. Although they concluded that the observation “seems to point a t some general law of the agency of electricity in chemical operations” ( I A ) , it was not until 1834 that this general law was documented ( 2 A ) . I t is clear then that electroanalytical chemistry was not part and parcel of the Colonial spirit. The situation is not dramatically different today; however, there are a number of favorable signs. The trend away from the cloistered academic fraternity of the 1950’s and 1960’s continues unabated. The users of modern techniques now far outnumber the several dozen proponents of only a few years ago. I t is clear that the Laplace transform-operational amplifier-digital simulationcomputer revolution is over and that finite current electrochemical methods are, in fact, finding many useful chemical applications. With this maturity, there has been a fall off in the rate of technique development. Over the past four years, this reviewer has found it increasingly difficult to ferret out those contributions which are more than an exercise in technique and truly hold promise for valuable future applications. There are quite a few “wheels” being reinvented, but little in the way of really novel stuff. Most of the exciting action has moved into the applications area. As in the past, the emphasis here will be directed toward nonelectronic experimental ideas and unique applications ( 3 A ) .The references listed were selected from several thousand possibilities based on the author’s subjective view. Chemical Abstracts, Chemical Titles, and the Interface Newsletter were searched from January 1974 through December 1975. Several books have been published recently which deal with the experimental aspects of electrochemistry. Sawyer and Roberts have described “Experimental Electrochemistry for Chemists” in a manner which will make it easier for “outsiders” to join in the application of electrochemistry to various chemical problems ( 4 A ) . For organic chemists Weinberg has edited an extensive two-volume treatise dealing with the “Technique of Electroorganic Synthesis” ( 5 A ) . Rifi and Covitz have written a much shorter introduction to the same subject ( 6 A ) .Gileadi and coworkers introduce
“Interfacial Electrochemistry” from the physical chemists’ point of view ( 7 A ) .Although limited in scope, this book is very readable and has many excellent sections. Meites and Zuman have organized a major work entitled “Electrochemical Data” ( 8 A ) . Anyone who doubts that this is an ambitious undertaking will be convinced by examination of the first volume on the electrochemical behavior of organic, biochemical, and organometallic substances. Data have been selected and compiled from publications for the 12year period from 1960 through 1971. The sections which follow are intended to provide only a loose structural framework for this review since many of the references cited contain information related to more than one section. ELECTRODES AND CELLS It’s often been said that electrochemistry would be useful if it weren’t for the electrodes. This shortsighted cynicism is popular with those who remember electrochemistry as clogged capillaries and dried-out agar salt bridges. These times are gone, but we really still don’t know very much about the surface chemistry of electrodes and how this influences electrode processes. Detailed electrochemical studies of surface adsorption and its effects are now really beginning to make some headway. Anson, for example, has recently reviewed his towering efforts in this regard ( I B ) . The application of spectroscopic techniques (see below) is also becoming more sophisticated and correlations with electrode kinetics are just now becoming practical. An entirely new approach has recently begun to surface. Why not prescribe the interface you want and synthesize it by covalently binding appropriate molecules to an electrode substrate? One of the neatest ideas to hatch in a few years is the “chiral electrode” devised in Larry Miller’s lab a t Fort Collins ( 2 B ) . In this case, an optically active amino acid was linked to carboxylic acid sites on air-oxidized graphite. The nice stable amide bonds afford a chiral environment in the interphase. Electrodes with both R and S configurations were prepared and demonstrated to produce optically active electrolysis products from inactive starting materials. This work is the first chapter in what promises to be one 9f the most exciting areas in preparative organic electrochemistry. ANALYTICAL CHEMISTRY, VOL. 48, NO. 5, APRIL 1 9 7 6
17R
