Anal. Chem. 1986, 58, 3 3 R - 4 9 R (R20) Gerbitz, K.-D.; Summer, J.; Thallemer, J. Ciin. Chem. (Winston-&/em, N . C . ) 1984, 3 0 , 382-6. (R21) Brockelbank, J. L.; Klm, J. B.; Barnard, G. J.; Gaier, B.; Kohen, F. Ann. Clln. Biochem. 1984, 2 1 , 284-9. (R22) Strasburger, C. J.; Wood, W. G. Fresenius’ Z. Anal. Chem. 1984, 317, 724. (R23) Krausz, H. S.; Tode, B.; Caldini, A. L.; Haritz, J.; Pazzagli, M.; Wood, W. G. Fresenius‘ Z . Anal. Chem. 1984, 317, 723. (R24) Campbell, A. K.; Patel, A. Biochem. J . 1983, 216, 185-94. 8. FLUORESCENCE FLOW CYTOYETRY (Sl) Steinkamp, J. A. Rev. Scl. Instrum. 1984, 5 5 , 1375-1400. (S2) Parks, D. R.; Herzenberg, L. A. Methods Enzymoi. 1984, 108, 197-24 1, (53) Cambler, J. C.;Monroe, J. G. Methods Enzymol. 1983, 103, 227-45. (S4) Muirhead, K. A. Trends. Anal. Chem. 1984, 3 , 107-11. (S5) Damjanovich, S.; Gaspar, R.; Tron, L.; Aszalos, A. Amer. Biotechnoi. Lab. 1985, 3 ( 5 ) , 11-21. (S6) Johnston, R. 0.; Bartholdl, M. F.; Hiebert, R. D.; Parson, J. D.; Cram, L. S. Rev. Scl. Instrum. 1985, 5 6 , 691-5. (S7) Tren, J.; Szollosi, J.; Damjanovlch, S.; Helliwell, S. H.; ArndtJovln, D. J.; Jovin, T. M. Biophys. J. 1984, 45, 939-46. (S8) Noronha, A.; Richman, D. P. J. Histochem. Cytochem. 1984, 3 2 , 821-6. (S9) Lutz, L. H.; Yayanos, A. A. Anal. Biochem. 1985, 144, 1-5. (S10) Bohmer, R.-M.; Papaioannou, J.; Ashcroft, R. E. J . Histochem. Cytochem. 1985, 3 3 , 974-6. (S11) Franklln, A. L.; Flllon, W. 0. Stain Technoi. 1985, 60, 125-35; Chem. Abstr. 1985, 103, 137934. (S12) Darzynklewicz, 2.; Traganos, F.; Kapuscinskl, J.; Staiano-Coico, L.; Melamed, M. R. Cytometry 1984, 5 , 355-63. (S13) Glazer, A. N.; Stryer, L. Biophys. J . 1983, 43, 383-6. (S14) Lee, G. M.; Thornthwalte, J. T.; Rasch, E. M. Anal. Biochem. 1984, 137, 221-6. (S15) Hamada, S.; Fujita, S. Hlstochemistry 1983, 79, 219-26. (S16) Greenspan, P.; Mayer, E. P.; Fowler, S. D. J . CellBiol. 1985, 100, 965-73. (S17) Latt, S. A.; Marino, M.; Lalande, M. Cytometry 1984, 5 , 339-47. (S18) Curtis, S. K.; Cowden, R. R. Histochemlstry 1983, 78, 503-11. (S19) Kroll, W. Histochemistry 1984, 80, 493-8. (S20) Zelenin, A. V.; Poletaev, A. I.; Stepanova, N. G.; Kolesnikov, V. A.; Nlkitin, S. M.; Zhuze, A. L.; Gnutchev, N. V. Cyfometry 1984, 5 , 348-54. (S21) Van Dilla, M. A.; Langlols, R. G.; Pinkel, D.; Yajko, D.; Hadley, W. K. Science (Washington, D.C.) 1983, 220, 620-2. (S22) Severin, E.; Stellmach, J.; Nachtigal, H.-M. Anal. Chim. Acta 1985, 170, 341-6. (S23) Tertov, V. V.; Orekhov, A. N.; Rudchenko, S. A.; Molotkovskll, Y. G.; Bergel’son, L. D. Doklady Akad. Nauk SSSR 1984, 274, 1238-41; Chem. Abstr. 1984, 101, 3383.
(S24) Nguyen, T. V.; Raber, M.; Barrows, G. H.; Barlogie, B. Science (Washington, D . C . ) 1984, 224, 876-9. (525) Maron, D.; Taylor, S. I.; Jackson, R.; Kahn, C. R. Diabetologia 1984, 2 7 , 118-20. T. FLUORESCENCE MICROSCOPY
( T l ) Ploem, J. S. I n “Analysis of Organic and Biological Surfaces”; Echlin, P., Ed.; Wiley: New York, 1984; pp 609-28. (T2) Kurtz, I.; Balaban, R. S. Biophys. J . 1985, 4 8 , 499-508. (T3) Seul, M.; McConnell, H. M. J. Phys. E. 1985, 18, 193-6. (T4) Hannon, D.; Quinton, P. M. Anal. Chem. 1984, 5 6 , 2350-1. (T5) Ware, B. R. Am. Lab. 1984, 16 (4), 16-28. (T6) Rink, T. J. Pure Appi. Chem. 1983, 5 5 , 1977-88. (T7) Dixon, D.; Brandt, N.; Haynes, D. H. J . Bioi. Chem. 1984, 259, 13737-41. (T8) Ashley, R. H.; Brammer, M. J.; Marchbanks, R. M. Biochem. SOC. Trans. 1984, 12, 869-70. (T9) Pozzan, T.; Rlnk, T. R.; Tslen, R. Y. Protein Conform. Immunoi. Signal (Proc. EM80 Workshop) 1983, 453-8; Chem. Abstr. 1984, 100, 19963. (T10) Ashley, R. H.; Brammer, M. J.; Marchbanks, R. Biochem. J . 1984, 219, 149-58. (T11) Grynklewicz, G.; Poenie, M.; Tsien, R. Y. J . Bioi. Chem. 1985, 260, 3440-50. (T12) Tsien, R. Y.; Rink, T. J.; Poenie, M. Ceii Calcium 1985, 6 , 145-57; Chem. Abstr. 1985, 103, 19229. (T13) Deber, C. M.; Tom-Kun, J.; Mack, E.; Grinstein, S. Anal. Biochem. 1985, 146, 349-52. (T14) Puchkov, E. 0.;Bulatov, I.S.;Zinchenko, V. P. FEMS Microbioi. Lett. 1983, 2 0 , 41-5; Chem. Abstr. 1983, 9 9 , 191554. (T15) Kubic, T. A.; King, J. E.; DuBey, I. S. Microscope 1983, 3 1 , 213-22. (T16) Fulcher, R. G.; Wood, P. J.; Yiu, S. H. Food Technoi. (Chicago) 1984, 3 8 , 101-6; Chem. Abstr. 1984, 100, 119367. (T17) Denyer, S. P.; Ward, K. H. J . Parenter. Sci. Techno/. 1983, 3 7 , 156-9. U. OTHERTECHNIOUESANDAPPLICATIONS (Ul) McCall, S. L.; Latz, H.; Ullman, A,; Winefordner, J. D. Can. J . Spectrosc. 1983, 28, 119-24. (U2) Tsuchiya, M.; Torres, E.; Aaron, J. J.; Winefordner, J. D. Anal. Lett. 1984, 17, 1831-41. (U3) Weisz, H.; Pantel, S.;Dilger, C. M.; Glatz, U. Mikrochim. Acta 1984, 1 , 69-83. (U4) Moody, R. P.; Weinberger, P.; Greenhalgh, R . Can. Tech. Rep. Fish. Aquat. Sci. 1983, 1151, 93-104; Chem. Abstr. 1984, 100, 46409. (U5) Alvarez-Roa, E. R.; Prieto, N. E.; Martin, C. R. Anal. Chem. 1984, 5 6 , 1939-44. (U6) Welnberger, R.; Cline Love, L. J. Spectrochim. Acta 1984, 40A, 49-55. (U7) Chen, R. F.; Scott, C. H. Anal. Lett. 1985, 18, 393-421.
Dynamic Electrochemistry: Methodology and Application Dennis C. Johnson* Department of Chemistry, Iowa State University, Ames, Iowa 50011
Michael D. Ryan Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53233
George S. Wilson Department of Chemistry, University of Arizona, Tucson, Arizona 85721
This review covers the literature for the approximate period of December 1983 through November 1985 and gives emphasis to progress in the theory and methodology of quantitative electroanalytical chemistry. Cited also is literature describing auxiliary techniques for characterization of electrochemical phenomena. Three areas of high activity and significance for this review period are noteworthy at the outset: Microelectrodes received increased attention because of the virtual steady-state response that is obtained in unstirred solutions and the increased signal-to-background ratio. The study of chemically modified
solid electrodes continued to increase in popularity with much creativity shown for incorporation of electroactive functional groups into a variety of conductive films. Also apparent is the increased emphasis on the development of modified electrode surfaces for catalyzing bioselective and biospecific faradaic reactions.
A. BOOKS AND REVIEWS Newcomers as well as veterans in electroanalytical chemistry can benefit immensely from “Laboratory Techniques in Electroanalytical Chemistry”, edited by Kissinger and
QQQ3-27QQ/86/Q358-33R~Q6.50/0 0 1986 American Chemical Society
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Heineman (16A). This text contains 24 chapters (751 pages) covering a broad range of experimental topics. Out of consideration for brevity, only a few are cited here: review of fundamentals, electronic instrumentation, electrodes, cells, solvents, supporting electrolytes, investigation of inorganic and organic reactions, photoelectrochemistry, and detection in liquid chromatography. Several additions appeared to series. Volume 13 of “Electroanalytical Chemistry”, edited by Bard @A),contains comprehensive reviews of spectroelectrochemistry by Heineman, Hawkridge, and Blount and chemically modified electrodes by Murray. Volume 15 of “Encyclopedia of the Electrochemistry of the Elements”, edited by Bard and Lund (3A), emphasizes reactions of derivatives of ammonia, by Reed and Wightman; and heteroaromatic compounds, by Baumgartel and Retzlav. Volume 13 of “Advances in Electrochemistry and Electrochemical Engineering”, edited by Gerischer and Tobias ( I I A ) ,contains a discussion by Barz, Bernstein, and Vielstich on use of turbulent hydrodynamic techniques for kinetic studies, a review by AdiiE of effects of metal adatoms on electrode reactions, and a description by Ross and Wagner of spectroscopic techniques for study of electrode surfaces. Four volumes were added to ”Comprehensive Treatise on Electrochemistry”, edited by Bockris, Conway, and Yeager, with assistance by Srinivasan, White, and others. Volume 7 (6A) includes chapters on electrode kinetics, by Krishtalik; electrocatalysis, by Appleby; and semiconductor electrodes, by Memming. Volume 8 (35A) emphasizes experimental methods with reviews on instrumentation, by McKubre and Macdonald; computer techniques, by Ridgway and Mark, and polarography, by Kuta. This useful volume also reviews several spectroscopic techniques for characterization of electrode surfaces: ESCA, by Hammond and Winograd; field ion microscopy, by Nanis; and electron microscopy, by Kampe. A bibliography of selected electroanalytical applications is included in volume 8, by Venkatesan. Volume 9 (36A) emphasizes the study of electrodics using non-steady-state techniques, by Epelboin, Gabrielli, and Keddam; ac techniques, by Sluyters-Rehbach and Sluyters; rotated disk and ring-disk electrodes, by Filinovsky and Pleskov; and thin-layer cells by Woodard and Reilley. Most recently, volume 10 (30A) features bioelectrochemistry with discussions of enzymatic bioelectrocatalysis, by Tarasevich; and a survey of electrochemical techniques in the biological sciences, by Findl, Strope, and Conti. Volume 9 of “A Specialist Periodical Report: Electrochemistry”, edited by Pletcher (23A),contains an extension of the discussion of porous electrodes, by Hampson and McNeil in volume 8, to flow-through electrodes and electrodes with a three-phase inferface. A review of semiconductor electrochemistry, by Peter; and a discussion of spectroelectrochemistry, by Robinson, are also included in volume 9. An extensive review of applications of flow-through electrochemical detectors in liquid chromatography was presented by Stulik and PacBkovB (31A). We note several publications of conference proceedings. The proceedings of the 7th International Symposium on Bioelectrochemistry, Stuttgart 1983, were published in serial form (19A). The proceedings of the Symposium on Electrochemical Detectors, London 1981, edited by Ryan (28A),included reviews of new electroanalytical techniques in medicine and biology by Albery and Haggett; voltammetric flow-through detectors, by Trojanek; detectors with renewable surfaces, by Tenygl; optimization of detection at a static mercury drop electrode for high-performance liquid chromatography, by Van Oort et al.; and tensammetry for detection of adsorbed surface-active compounds, by Kalvoda. Volume 18 (Part A) of ”Analytical Chemistry Symposia Series” contains proceedings of the Symposium on Electrochemical Detection in Flow Analysis, MBtrafiired, Hungary, 1982, edited by Pungor and Buzas (24A). The proceedings of the Course on Bioelectrochemistry in the Eleventh International School of Biophysics, Erice, Sicily, Italy, 1984, were published as volume 11 of ”Ettore Majorana International Science Series”, edited by Milazzo and Blank (20A). The proceedings of the 6th Australian Electrochemistry Conference, Geelong, Victoria, 1984, edited by Rand and Bond (26A),includes papers on organic and bioelectrochemistry, as well as semiconductor and spectroelectrochemistry, surface studies, and trace electroanalysis. 34R
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We noted at the outset the enthusiasm reflected in the growing literature on the subject of bioelectrochemistry, and this fact has been noted in reviews and proceedings cited above (ZOA,26A, 28A, 30A). Also noteworthy are the brief introductions to electroanalytical techniques in the clinical laboratory by Purdy (%A) and by Czaban @A). A more extensive review was by Hirst and Stevens (14A). The popularity of various forms of carbon electrodes has persisted along with efforts to increase surface reactivity for amperometric and voltammetric applications. Extensive reviews of carbon as an electrode material can be found by Gross and Jordan (12A),Edmonds (9A),and, in the Russian language, by Tarasevich (32A). The application of stripping voltammetry for trace metals was reviewed by Florence (10A). The determination of trace metals in natural water environments, predominantly by differential pulse voltammetry, was reviewed by Niirnberg (21A). The highly sensitive technique of square wave voltammetry was reviewed briefly by Osteryoung and Osteryoung (22A),and square wave voltammetry at microelectrodes was reviewed by Sleszynski (29A),with specific application to SnOz electrodes in the absence of reversible electron transfer. Stripping analysis in a form called “adsorptive stripping voltammetry” is applicable for trace levels of many electroactive organic species and was reviewed by Wang (34A). The increasing utility of photoelectrochemical detection was reviewed by LaCourse and Krull (17A). Several reviews in series have been cited related to spectroscopic characterization of electrode surfaces (11A, 26A, 35A). Habib and Bockris (13A) reviewed Fourier transfer IR spectrometry at the solid-solution interface, and Brodsky et al. (4A) reviewed the interpretation of data from electrochemical optical spectroscopy of metals. Recommendation is given, also, to the discussion of electron energy loss spectroscopy by Avouris and Demuth ( I A ) . Chronic concerns persist in electroanalysis over the presence of electroactive impurities in solvents. Coetzee and Chang (5A) discussed purification of nonaqueous solvents, and Wallace (33A) described the dilemma of dissolved oxygen, especially for cathodic detections, and discussed several recent efforts to circumvent the problem. The use of nonlinear regression and pattern recognition is reviewed by Rusling (27A) for interpretation of electroanalytical data, resolution of unresolved i-E curves, and identification of reaction mechanisms. Cussler (7A)has reviewed diffusion in fluids. Although not directed specifically to the electroanalytical chemist, this is a useful review of the fundamentals of mass transfer. Of miscellaneous note are the “Dictionary of Electrochemistry”, by Hibbert and James (15A);and a review of recommended terms, symbols and definitions, by Meites, Zuman, and Nuernberg (18A).
B. MASS TRANSFER The Cottrell equation, i = ~ F A ( D / T ~ )gives ~ / ~the C ~dif, fusion limited response of an electrode immediately following a step change of applied potential to change the surface concentration from the homogeneous bulk value (Cb) to zero. This equation, for small t, is appropriate regardless of electrode geometry and rate of solution agitation so long as the Cottrell diffusion-layer thickness is much less than the hydrodynamic boundary layer thickness. In spite of its simplicity,the Cottrell equation has been of great significance in dynamic electroanalysis because of implications for maximizing analytical sensitivity, i.e., i/Cb m for t 0, and for kinetic studies in which a high mass transfer rate, ( D / ~ t ) l / ’is, desirable to enhance the sensitivity to a coupled kinetic rate. Jan et al. (20B) described a laser-based optical technique for spatial imaging of the diffusion-layer region of the electrode-solution interface. Gottesfeld and Feldberg (16B)presented an analysis of the semiinfinite linear diffusion at bounded planar electrodes for long t under low-frequency perturbations of surface concentration. Hempstead and Oldham (I7B) described a mathematically based filtration technique for determining the Cottrell component of more complex transient signals obscured by current components having differing time dependence. Nonlinear diffusion at the edges of unbounded planar electrodes results in deviation from the simple Cottrell equation at long t. Ikeuchi et al. (19B)offered experimental
-
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DYNAMIC ELECTROCHEMISTRY
& electrodes. app1iCatiOn 01 pulsed potential ampromshlc detection lor organb ./
of insulation geometry of a m i d i s k and concluded that the infinite plane model is useful as long as the radius of the insulation is at least twice that of the electrode. Aoki et al. (18)have extended the theory to linear sweep voltammetry and chronopotentiometry at micro-disk electrodes; an approximate equation was recommended for the simple evaluation of diffusion coefficients. Wehmeyer et al. (388) considered the response of microband electrodes. They reported that sigmoidal i-E curves are obtained and the sensitivit of microelectrdes was illustrated by detection to ca. 7 X 102M. Kovach et al. (218)presented results for micro-cylindrical, band, and tubular electrodes. Independence of response for micro-tubular electrodes in flow-through cells was observed for flow rates to 3 mL min-l. Application of extremely high potential scan rates at microelectrodes was considered by Howell and Wightman (188). Steady-state limiting plateaus were obtained on i-E curves at a micro-disk electrode to 3.0 V minP; at scan rates above 200 V s-', i-E curves were characteristic of planar diffusion. Aoki et al. ( 2 8 ) have considered linear sweep voltammetry a micro-cylindrical electrodes. ODea et al. (248) have described square-wave voltammetry a t microelectrodes, and Schuette and McCreery (308)applied square wave voltammetry with synchronous demodulation a t a micro-disk. Weymeyer and Wightman (378) presented experimental results for cyclic voltammetry and anodic stripping voltammetry at a Hg micro-hemispherical electrode. Penczek and Stojek (258)presented the theory for stripping voltammetry a t a micro-disk mercury-film electrode. Arrays of microelectrodes have been of much interest for reasons including a large collective electrode current. Sleszski et al. (338)compared current densities at microarrays ased on reticulated vitreous carbon with normal glassy carbon. Shoup and Smbo (328)used the wded "hopsmtch" algorithm for simulation of the i-t response of ensembles of micro-disk electrodes. Reller et al. (278)used a two-dimensional expanding grid method of digital simulation for microelectrode ensembles. Ciszkowska and Stojek (9B)reported satisfactory agreement of experimental results with stripping theory for a graphite based array of micro-disk mercury electrodes. Thormann et al. (358)described use of lithography for production of linear gold and platinum microelectrode arrays. Bond et al. (68)discussed the voltammetric applications of microelectrodes in very dilute supporting electrolyte solutions. Practical mercury drop and dropping mercury electrodes are not perfectly spherical and continued attention is given to deviations of experimental response from theoretical predictions based on assumptions of spherical and unshielded geometries. The general problem was considered by Bond and Oldham ( 7 8 ) . I t was demonstrated that the customary plot of In (id - O/i vs. E for reversible reactions is without quantitative significance when deviation from sphericity is significant. Alternative plots are suggested under all circumstances for obtaining kinetic and thermodynamic parameters. Galvez ( 1 4 8 ) presented rigorous solutions to account for sphericity of the DME for reversible electrode reactions in normal pulse, reverse pulse, and differential pulse polarography. Finally, Galvez and Alcaraz (158) considered chronopotentiometry at a DME, accounting for effects of electrode sphericity in the study of preceding chemical reactions. Hydrodynamic electrode systems continued to receive a t tention for studies of heterogeneous and coupled homogeneous kinetics, 88 well as for quantitative determination of chemical concentrations. McLaughlin (238) reconsidered analytical solutions to the Nernst-Planck equation of convective-diffusional mass transfer and pointed out that omission of inertial effects can be a significant deficiency. Steady-state measurements of kinetic effects are most sensitive when the rate of convection is large, and Barz et al. ( 5 8 )gave an excellent review of the investigation of electrochemical reactions by application of turbulent hydrodynamics. The consideration includes rotated disk, ringdisk, and cylindrical electrodes and tubular and channel electrodes. Epelboin et al. (12B)presented an excellent review of transient response from steadystate conditions under small and large amplitude perturbations. This includes perturbations of physical parameters (area, pressure, temperature, concentration, and rotation speed) as well as electrical (step and sweep of potential and current).
r & in
1967. Hi; cwrent research interests include structural effect^ on me elemon bansler PIopnleS Of proteins. panicula* cytochromes. the redox chemistry of 0Tga"oSun"r canpands. and me propemes of immobilized potelns. M k h are used as bb@ical W l s and la the development 01 cllniCB1 blosensas.
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verification of an earlier equation for limited current at unshielded electrodes. Shoup and Smbo (328)described an algorithm, called 'hopacotch" for the rapid and accurate numerical simulation of mass transport phenomena. The technique was illustrated for Cottrell transport with and without a coupled chemical reaction. There are numerous useful hydrodynamic electrode sy&ms that do not represent well-defined geometric models for which analytical solutions of the Nernst-Planck equation have not been obtained. Pratt (268) suggested the estimation of the steady-state diffusion layer thickness from a comparison of the steady-state response under hydrodynamic conditions to the transient i-t response in unstirred media. This calculation requires knowledge of the diffusion coefficient of the electroactive species. Diffusional transfer under bounded conditions in thin-layer cells received a useful renew bv Woodard and Reillev (398). Included were a brief Consideration of theory, a desgription of cell design, and applications; spectroelectrochemical thinlayer cells were considered also. Receiving great emphasis in the dynamic electroanalytical literature was mass-transfer limited response a t microelectrodes. A microelectrode is one with a surface dimension less than the diffusion layer thickness. Several analytical consequences of significance immediately appear: (i) Electrode currents are small and iR,,,, loss can be negligible even for poorly conducting media. (ii) Furthermore, low iR," loss can allow for use of the more simple and electrically quieter two-electrode potentiostatic systems. (iii) Steady-state response is expected, which is independent of solution agitation, and sigmoidal rather than peak-shaped i-E curves are obtained. Aoki and Osteryoung ( 3 8 )reviewed the development of the theory of micro-disk electrodes and provided a general solution for the i-E response of reversible reactions. Shoup and Szabo (318)considered the influence on the i-t reswnse
A N M Y T I C M C M M I S T R Y , VOL. 58. NO. 5. APRIL 1986
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Rotated disk and ring-disk electrodes (RDE and RRDE) continued to be the focus of much research interest in hydrodynamic electrode systems. A general survey of the theory and application of RDE and RRDE systems was offered by Filinovsky and Pleskov (13B). Verney et al. (36B) described a metal/n-type semiconductor RRDE and the experimental determination of its collection efficiency. Digital simulation techniques continued to be of great importance to verify complex reaction mechanisms in hydrodynamic voltammetry. Eddowes (1IB) discussed finite-difference and orthogonal collocation methods. Both methods reduce the ordinary differential equations to a set of simultaneous equations that can be readily solved for coupled kinetic and convective diffusion problems. Levart (22B)used a multiring model for the numerical simulation of the convective diffusion problem at partially blocked RDE surfaces. The hopscotch simulation was already mentioned (32B). The theory and application of sinusoidal hydrodynamic modulation (SHM) of mass transfer rates a t the RDE by Bruckenstern, Miller, and co-workers appears to be reaching a state of maturity. Rosamilia and Miller (28B)discussed the frequency response of SHM and the determination of diffusion coefficients. This technique does not require knowledge of the concentration or the number of electrons for the electrode reaction; application was demonstrated for dissolved 02. Rosamilia and Miller (29B)have given also a very important consideration of the interaction of modulation frequency, electrode potential scan rate, and signal filtering for sinusoidal hydrodynamic modulation. Deslouis and Tribollet (10B) considered the difficulty of applying the existing theory over a large frequency range of the sinusoidal modulation and offered asymptotic approximations in the low and high frequency domains. Swathirojan and Bruckenstein (34B) illustrated applicability of the SHM technique at a RDE to the potential region where solvent undergoes faradaic decomposition and studied the neutralization of H+ in a dilute solution of strong acid by OH- produced during cathodic decomposition of H20. The separability of the mass-transfer and nonmass-transfer-controlled components of the SHM technique was demonstrated. Austin et al. (4B) applied square-wave hydrodynamic modulated voltametry at a RDE to the anodic oxidation of I- a t Pt in the potential region of O2 evolution.
C. FLOW-THROUGHDETECTORS Thin-layer (channel) flow-through cells containing single electrodes remain popular for flow-injection and chromatographic detection. Applications are now rather commonplace and shall go without general notice here. A recent review by Stulik and Pacbkovii (33C) is recommended for general background information. Imaginative development continues on the use of cells with multiple electrodes, arranged in series or parallel. Roosendaal and Poppe (31C)presented approximate derivations for the electrode currents at flat single and dual (series) electrodes under Poiseuille flow. Aoki et al. (9C) derived an equation for the transient current at the downstream electrode when a galvanostatic step is applied at the upstream electrode. Lunte et al. (25C) described the analytical advantages obtained using dual-electrode thin-layer cells in both the parallel-adjacent and the series configurations. Matson et al. (26C) extended the concept of dual electrodes to an array of coulometric electrodes and claimed advantage for electrochemical resolution of coeluting species in chromatographic applications. Anderson, with Moldoveanu and Handler, has presented a theoretical consideration (27C) and numerical simulation (7C)for the response of a flat electrode in a rectangular channel, as well as for two parallel plate electrodes (29C). Wang and Freiha (37C)described a rotated disk electrode in a thin-layer cell for flow-injection and chromatographic analysis. Tougas et al. (35C)presented the theoretical and experimental response of a biamperometric detector in a flow stream with a small A 8 applied across the two electrodes. Curran and Tougas (12C) described the use of reticulated vitreous carbon for flow-through electrodes, which can operate as coulometric detectors (96,485 C equiv-') at flow rates less than 1.0 mL min-'. Microelectrodes have been considered for use in flowthrough detectors; advantages can include lower dead volume, smaller iR loss, and lower flow-rate dependence of limiting currents. As the ultimate in low dead-volume, Knecht et al. (21C) inserted a single 9-pm carbon fiber electrode into the 36R
ANALYTICAL CHEMISTRY, VOL. 58, NO. 5, APRIL 1986
end of an open-tubular LC column (15 pm i.d.). Moldoveanu and Anderson (28C) described the numerical simulation for an array of microelectrodes in one wall of a flow-through cell. Anderson et al. (SC) also illustrated the usefulness of array detectors at potentials beyond the potential limit for solvent breakdown for which the signal-to-background ratio is more advantageous than for a single electrode of area equal to the combined areas of the array. Cope and Tallman ( I l C ) calculated the convective diffusion current at a single strip microelectrode in a flow channel. Flow-through detectors of the wall-jet configuration have continued to receive attention because of the claim for high mass transport rates achieved with very small jet diameters. An equation of response was derived by Gunasingham and Fleet (16C),who also described a ring-disk wall-jet detector as a unique and symmetric example of dual (series) electrodes. The wall-jet design and applications were considered further by Gunasingham (15C), and Gunasingham et al. (17C) considered the apparent differences in sensitivity when applied for normal-phase and reverse-phase chromatographic detection. Dalhuijsen et al. (13C) reconsidered the theory of the wall-jet electrode, and Albery (1C) described the analytical solution for the current distribution at the electrode. Albery and co-workers have presented the theory for a new dual (series) detector in which a packed bed electrode was placed immediately upstream from a wall-jet electrode (3C),derived the response of the wall-jet ring-disk electrode (2C),and used this detector for indirect detection of proteins by generation of Br2 a t the disk and detection of excess reagent at the ring electrode (4C). Elbicki et al. (24C) considered the optimization of amperometric detectors in flow-through cells based on integration of the steady-state hydrodynamic response. They applied the results specifically to a comparison of wall-jet and thin layer cells and examined the geometric parameters for which their sensitivities are equivalent. The analytical sample throughput of voltammetric analysis can be increased significantly using flow-injection concepts of sample handling, as compared to the traditional batch operations in cells of large volumes. A consideration of linear sweep voltammetry a t a dropping mercury electrode in a flow-through cell was given by Kowalski and Kubiak (23C) as a function of the direction of fluid flow relative to mercury flow in the capillary, and conditions were examined for independence of current on fluid velocity. Rapid sweep rates are useful for increasing the throughput of flow-injection voltammetry as well as for voltammetric resolution of overlapping peaks in chromatographic analysis. Alexander and Akapongkul(5C) described differential pulse voltammetry at a Cu-amalgam electrode in a flow-through cell with 100-ms repetition times allowing scan rates to 100 mV s-*. Reardon, O'Brien, and Sturrock (30C)described a computer-controlled instrument for applying rapid-sweep square-wave voltammetry with automated data processing. Tougas and Curan (34C) described the use of stopped-flow liner sweep voltammetry at a reticulated vitreous carbon electrode. Wang and Dewald (36C),Wise et al. (39C), and Wechter et al. (38C) have all described stripping voltammetry in flow-injection systems. Barnes and Nieman (1OC) have expanded the use of coulostatic pulse amperometric detection with a 10-point voltammogram obtained in 1-2 s with detection limits in the picomole range for aminophenols. Kok, Brinkman, and Frei (22C) presented results for the chromatographic determination of phenols using on-line electrochemical generation of Br2 with subsequent detection downstream of the excess reagent. LaCourse et al. (24C) presented a highly useful description of the application of a photoreactor followed by electrochemical detection of the photoproducts for flow-injection and chromatographic analysis. Applicable for the optimization of detector design is the consideration of Shih and Carr (32C) of the flow-rate dependence of postcolumn reactors and the effect of reactor length. Whereas a review of dynamic electroanalytical techniques would not normally include potentiometric detection, notice is given here of several recent examples of potentiometric detection in flow-through cells. Alexander, Haddad, and Trojanowicz (6C)used a copper wire electrode for amino acids and other copper-complexing ligands. Hitchman and coworkers have extended this type of detection to proteins at silver electrodes (18C, 19C) and copper electrodes (20C);
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electrochemical pretreatment of the electrode surfaces was found beneficial for greater reproducibility.
D. HETEROGENEOUS/HOMOGENEOUS KINETICS The elimination of uncompensated resistance in voltammetric methods has been seriously examined for at last 20 years. During the past 2 years, renewed interest in this topic has been sparked by two major factors: the use of microelectrodes and attempts to obtain accurate heterogeneous rate constants, k,. The small currents that are generated at microelectrodes, which drastically reduces the iR drop, have allowed for significantly increased scan rates that are easily accessible by voltammetric methods. Notably, Howell and Wightman ( 3 6 0 , 3 7 0 ) have demonstrated the use of microvoltammetric electrodes for ultrafast voltammetry and for highly resistive solutions. Bond et al. have demonstrated the use of these electrodes in highly dilute solutions ( 8 0 ) or solutions without supporting electrolyte ( 9 0 ) . In fact, these electrodes are usable down to the freezing points of the solvents (100). It was also shown that, because of the small currents involved, a two-electrode system was sufficient. Mercury films have been deposited on graphite microelectrodes, which have been used in cyclic ( 7 8 0 ) and anodic stripping voltammetry (610, 180). Because the product of the electrode reaction diffuses out radially and is hence diluted, second-order reactions of the electrode product are severely attenuated. As a result, microelectrodes can be used to determine the number of electrons in the electrode reaction, even if a catalytic or disproportionation reaction is occurring (60). Finally, microelectrodes have been applied to the study of homogeneous EC, CE, ECE, and disproportionation reactions (240). The effect of uncompensated resistance with conventional electrodes has not been ignored over the past 2 years either. Its influence on the evaluation of rapid electrochemical reactions was critically examined (550),along with the general question of the reliability of k , values for fast electrode kinetics (290). The effect of uncompensated resistance in linear sweep voltammetry was examined by Eliason and Parker (210),while Kadish et al. ( 3 8 0 ) measured the resistance of nonaqueous solvent systems and evaluated the k, values of the ferrocene/ferrocenium couple in those solvents. The generation of theoretical voltammograms by the use of the finite difference method was the subject of a number of reports recently. The general motivation was to utilize this method to reduce the computation time, which can be quite large for fast reactions or pulse techniques. The explicit method, with an exponentially expanded space grid, was described by Conti et al. (190) and applied to differential pulse polarography (reversible reduction and dimerization mechanism). Lasia (450)and Heinze et al. (330)applied the implicit method to cyclic voltammetry. Magno et al. described the use of digital simulation to very fast chemical reactions (480, 490). Ruzic ( 6 8 0 ) extended a method, the heterogeneous equivalent, which was best for very fast reactions to slow pseudo-first-order homogeneous kinetics. Shoup and Szabo (730) applied a digital simulation method called “hopscotch” to electrochemical problems. The use of semiintegration and integration in voltammetric methods was the subject of several reports. Bond et al. (110) described an efficient method for analyzing heterogeneous kinetics by using three-dimensional analysis of the variables, E , i, and m (the semiintegral). The semiintegral allows the direct computation of the surface concentrations, and this was applied to ferric oxalate and cadmium reductions (580). The integral of cyclic voltammograms, which has some unique properties, also was investigated (570). Namely, the net charge in a cyclic scan was shown to be proportional to concentration and free from capacitive contributions. The peak in the integrated voltammogram occurs in the reverse scan when i = 0 and, hence, should be free of iR drop. More efficient methods of analyzing and fitting voltammetric data were reported also. Bontempelli et al. (120) developed a simple relationship for calculating peak current ratios in cyclic voltammetry. Myland and Oldham (56D)developed a general method for relating the current at a spherical electrode to the current at a planar electrode for any wave form (reversible process). The reports of theoretical responses of voltammetric and chronoamperometric methods to a large variety of electro-
chemical mechanisms, including heterogeneous/ homogeneous kinetics and adsorption, are much too numerous to enumerate here. This section of the review will focus on new and/or important mechanisms or new insights into old mechanisms. The integaction between the reduced (or oxidized) product with other species in solutions has given rise to a number of “nuances” that are slowly being identified. For example, Pletcher (620) has observed that internal redox catalysis can significantly reduce the product selectivity in the controlled potential electrolysis of polyfunctional compounds. The effect of the redox reaction between the product of the first wave on the height of the second wave, where the species have different diffusion coefficients ( 2 0 ) ,was examined, along with the interaction between different redox couples (630). The dimerization reaction after a slow electron transfer was examined (220),where the dimerization significantly affects the apparent k, value. Theoretical and experimental studies of homogeneous redox catalysis ( 6 9 0 ) and the kinetics and mechanism of self-protonation reactions (10)were reported. Related to this, the relative kinetic acidities of weak acids were investigated by their rate of protonation of electrogenerated bases (410). The complexity of homogeneous reactions is exemplified by the report of Hebert et al. ( 3 2 0 ) on the question of whether aromatic anion radicals and dianions are redox reagents and/or nucleophiles. In this report, optically active reagents were used to investigate the reaction mechanism, and a competition between the redox and SN2 pathway was observed. Theoretical studies of linear sweep voltammetry for thinlayer electrodes were reported by several workers, including the cases where the electron transfer was quasi-reversible or irreversible ( 3 0 ) ,the thin-layer cell was immersed (350),the square scheme was considered (470), and the analysis of semiinfinite linear diffusion was done (300). The response was reported for pulse and differential pulse polarography applied to EE mechanisms (7601, irreversible (150) and quasi-reversible (520) electron transfers, CE mechanisms ( 5 3 0 , 5 4 0 , 2 6 0 , 1 6 0 ) ,CEC mechanisms (160),and dimerization mechanisms (200). Methods of reducing or correction for charging current in pulse methods were also described. A background compensation method in fast scan square wave voltammetry and other pulse methods at a DME ( 2 3 0 )was reported, as was a quick charging pulse polarographic method (640). A computational method of correction for charging current in dc polarography also was described (40). The use of superimposed potential perturbations at a static electrode was examined (510). Galvez examined electrode sphericity effects in normal, reverse, and differential pulse polarography (250),Baecklund et al. investigated precision in differential pulse and alternate-drop differential pulse polarography ( 5 0 ) , and Chen et al. (17 0 ) examined the temperature dependence of polarographic currents. Triple potential step chronoamperometry was applied to electrode processes involving a quasi-reversible electron transfer followed by an irreversible reaction (770). The catalytic mechanism was used by Kaneko ( 3 9 0 )to determine electrode reaction parameters of Ti(1V) and uranium. The effect of unequal diffusion coefficients on the voltammetric current functions for a pseudo-first-order EC catalytic mechanism was examined in detail (70). A use of the turbulent pipe flow method to study a very fast chemical step (k = 5 X lo’ M-l s-l ) between two charge transfers was reported (340). The effect of low ligand concentrations on cyclic voltammograms (400) and the use of normalized potential sweep voltammetry to second-order homogeneous reactions ( 6 0 0 )were described. The formalism of the square scheme for potentiostatic studies (700) and the nine-member square with isotopic electron exchange reaction ( 4 6 0 )were investigated. Struys et al. (750) rewrote the theoretical expressions for the faradaic admittance and the faradaic demodulation voltage without any specification of the mechanism of the electrode reaction. This should provide a framework for future quantitative studies. The development of voltammetric theory for a wide variety of mechanisms is extremely important, but the application of these theories has been severely limited because of the computational difficulties in fitting experimental data to theoretical curves. In particular, few electrochemical mechanisms fit into the neat categories that we, as electrochemists, have defined. Most reactions of general chemical interest are complicated by slow electron transfer kinetics and multiple ANALYTICAL CHEMISTRY, VOL. 58,
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reaction pathways. After all, how many s nthetic reactions lead to only one product with 100% y i e d Thus, for most electrochemical mechanisms it is necessary to evaluate several independent parameters. This can be done by trial and error, which is quite tedious and will give no assurance that the best solution has been obtained. Rusling (670) has developed a method of fitting theoretical voltammograms to the experimental data, which can speed up the trial-and-error process. A more promising approach, though, is the method reported by Speiser ( 7 4 0 ) ,which uses a multiparametric estimation of several rate constants, using essentially a three-dimensional working curve. Brown et al. ( 1 4 0 ) have used the Kalman filter, a recursive linear estimator, to estimate electrochemical charge transfer parameters. Related to the question of determining the electrochemical parameters is the assessment of their accuracy and the examination of sources of systematic error. This latter question has been probed by RodriguezMellando et al. (6601, while the former has not yet been critically addressed. The measurement of the Peltier heat of adsorption and desorption of hydrogen and oxygen from a platinized platinum electrode was described using a new heat responsive electrode (710, 7 2 0 ) . The theoretical principles of an acoustoelectrochemical effect have been examined by Gurevich ( 3 1 0 ) . In this work, the increased rate of electrochemical reaction significantly exceeded the amount predicted simply by an increase in mass transport. Gautheron et al. reported an ultrasound induced electrochemical synthesis of selenide and telluride anions (280). Klima et al. (430) used spin trapping to detect radical intermediates in the electrooxidation of substituted 1,4-dihydropyridines. There were a number of reports of the use of galvanostatic and coulostatic methods for kinetic studies. Nagy (590)used computer curve fitting to find the optimum time scale for relaxation techniques such as the galvanostatic, coulostatic, and potentiostatic methods. The coulostatic method was also applied to the study of highly reactive intermediates formed by 30-11s X-ray pulses ( 1 3 0 ) ,to the response of a phthalocyanine photoconductor electrode to a pulsed laser (650),and to relaxation kinetics in molten salts (420). The galvanostatic double-pulse method was used to study the electrode kinetics of bismuth oxidation (440),while the galvanostatic interrupter method was used to study polarization during the discharge of lead dioxide electrodes (270). A fast performance galvanostatic pulse technique was used to evaluate the ohmic potential drop and capacitance of the interface between two immiscible electrolyte solutions ( 5 0 0 ) .
E. SURFACE EFFECTS Although much attention has been given to electrocatalytic phenomena in the last 2 decades, the direct participation of electrode surfaces in faradaic reactions mechanisms, as well as the indirect effects of the interfacial environment on heterogeneous rate constants, still represents a relatively unknown frontier in chemical sciences. Except for all but the simplest of model reactions, the complete mathematical description appears to be an intractable problem. Appleby (2E) has presented a fairly general review of developments in electrocatalysis. The electrocatalytic effects of foreign metal ad-atoms on organic oxidation reactions at noble electrodes remained of interest and AdiiE ( I E ) has provided a review of the subject. In general, anodic reactions involving transfer of oxygen from the aqueous solvent to the oxidation products are slow and of marginal use in analytical amperometry. Austin et al. (4E) cited numerous references where electrocatalytic involvement of surface oxygen/oxide was suspected. The oxidation of As(OH)~to OAS(OH)~ appears to be a useful model reaction for study of anodic 0 transfer; Kao and Kuwana (25E) and Cabelka et al. (IOE)reported on kinetic studies of As(OH), at platinum electrodes in acidic media. Cox and Kulezza (12E) reported the catalysis of the AS(OH)~oxidation at a glassy carbon electrode by a thin surface film of mixed-valent Ru(II1,II) cyanide. Bruckenstein and Shay (9E) reported an ingenious study of the adsorption of oxygen at a gold electrode using an oscillating quartz crystal for in situ determination of the resulting weight change. Voltammetric responses reported for carbon electrodes are highly dependent on strate ies of surface pretreatment and active investigation persisteI f to find procedures for increasing reversibility, especially for glassy carbon surfaces. Kazee et 38R
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al. (26E) reported evidence that the customary process of mechanical polishing of glassy carbon produces a thin surface layer of dislodged carbon particles. Application at large positive voltages was reported to increase surface activity by Wightman et al. (57E),by Engstrom and Strasser (15E),and by Wang and Hutchins (54E). The resultant enhancement of surface activity was attributed to an increased coverage by oxygen-containing functional groups (15E,57E) and surface roughening (54E). Deakin et al. (13E) reported on the pH effect observed in the apparent heterogeneous rate constants for three redox couples at anodically activated glassy carbon electrodes and concluded the results were consistent with the presence of weakly acidic functional groups on the carbon surface. Quinhydrone on a glassy carbon surface was reported by Gomathi and Rao (17E)to catalyze oxidation of ascorbic acid. Heat treatment of glassy carbon under vacuum was demonstrated by Fagan et al. (16E)to produce an active surface for oxidation of ascorbic acid as well as a decreased background chargin current. Other evidence indicated loss of surface oxygen juring the heat treatment, and higher surface activity was attributed to a greater density of active sites resulting from exposure of fresh carbon. Hu et al. (21E) suggested that slow in situ loss of surface activity can result from impurity adsorption on glassy carbon, as is commonly observed for activated platinum surfaces. Research on the chemical modification of electrode surfaces for electrocatalysis is considered elsewhere in this review; however, three citations seem appropriate here in conjunction with activation of carbon surfaces. Urbaniczky and Lundstrom (48E)reported that electrode capacitance and kinetics at carbon paste electrodes are influenced by the composition of the paste. Takeuchi and Murray (47E)dissolved iron and manganese tetraphenylporphrin into the paste mixture and observed electrocatalysis currents in the presence of 02. Takahashi and Yoshida (46E)reported on surface properties of carbon materials modified by ion implantation. The last citation related to carbon recognizes the investigation by Oren and Saffer (33E) on double-layer charging currents at graphite cloth electrodes. Fast and slow processes were diagnosed; the slow process was concluded not to be related to changes in oxidation or ionization state of the surface nor to existence of micropores. Finally, mass transport and kinetics in the surface layer of modified electrodes were considered by Albery and Hillman (3E). Six cases were identified and simple expressions were given for evaluation of the electrochemical rate constant. Sangaranarayanan and Rangarajan (39E) reported extensively on the theory of modeling the adsorption of organic compounds. Koppitz et al. ( B E )reported on thermodynamic experiments to determine the electrosorption valency of organic adsorbates. Charge transfer and, consequently, bond formation were concluded to be important for some sulfurcontaining compounds. The influence of reactant adsorption in polarography continued to receive attention, with most recent activity focused on pulse techniques by Mas et al. (32E), Puy et al. (37E),LovriE (31E),Komorsky-LovriE and LovriE (27E),van Leeuwen (49E),Holub and van Leeuwen (20E), and by van Leeuwen et al. (50E). Rusling and Brooks (38E) reported on use of double-potential step chronocoulometry for determination of surface concentrations. Superb experimental work on voltammetric characterization of oriented chemisorbed molecules at polycrystalline platinum electrodes was reported by Hubbard and co-workers. Soriaga and Hubbard (43E) reported on temperature studies for some reversible redox, irreversible oxidation, and reductive desulfurization reactions. They also pointed out deficiencies that can result from interpretations of adsorption measurements based on hydrogen codeposition or anodic oxidation (43E). Studies of adsorption of hydroquinone also were reported as a function of electrode potential (11E)and weakly surfaceactive supporting electrolytes (42E). Analytical applications of stripping voltammetry for adsorbed electroactive organic molecules have been examined extensively by Wang and co-workers and recent contributions are cited for chlorpromazine at carbon paste electrodes (55E) and sex hormones (53E) and bilirubin (56E) at static mercury-drop electrodes. Lam and Kopanica (3OE)determined trichlorobiphenyl, and Sawamoto (40E)determined riboflavin at mercury electrodes. Bond et al. (7E) determined ethyny-
DYNAMIC ELECTROCHEMI STRY
lestradiol at a mercury electrode by normal pulse stripping voltammetry. Iwamoto and Osteryoung (23E) applied cathodic stripping voltammetry for thioamides adsorbed at rotated silver-disk lectrodes. Polta and Johnson (35E) took advantage of the inhibition of adsorbed nonelectroactive adsorbates on formation of surface oxide on platinum for the indirect, pulsed amperometric detection in a flow-through cell. The tensammetric technique has received renewed recognition for detection of surface active molecules at mercury electrodes in research described by Bos e t al. (8E) for determination of detergents and by Bednarkiewicz and Kublik (5E)for polyglycols. The greatest contribution to a quantitative understanding of surface effects at solid electrodes is coming from results of spectroscopic surface analysis correlated to observed electrochemical phenomena. Ellipsometry was one of the earliest techniques used and the subject was reviewed by Greef (18E).The application of election spectroscopy for chemical analysis (ESCA) for electrode surface studies was reviewed by Hammond and Winograd (19E). Primary movers in spectroscopic and electroanalytical studies of well-defined electrode surfaces are Hubbard and co-workers. Stickney et al. (44E, 45E) have discussed results of Auger spectroscopy and LEED on ordered ad-layers formed at Pt(ll1) surfaces immersed in aqueous solutions. Anionic ad-layers were found to act as cation exchangers. Wagner and Ross (52E) used LEED spot profile analysis of electrochemically treated Pt(100) and Pt(ll1) surfaces to demonstrate that the cyclic generation with dissolution of surface oxide results in surface reconstruction. Kaman et al. (24E) applied electron spectroscopy to glassy carbon electrode surfaces and found a high oxygen content in the outer 20-30 pm of a highly polished surface. Results of photoemission spectroscopy, secondary ion mass spectrometry, and electron spectroscopy were correlated with electrochemical data from the electrochemical activation of glassy carbon by Picq et al. (34E). Methods for in situ spectroscopic surface analysis remain few. Kordesch and Hoffman (29E) described an electrochemical cell designed for in situ EXAFS of “wet” electrodes. Application was described for iron passivated in buffered borate media. Surface enhanced Raman spectroscopy (SERS) still receives serious attention, even though not a general technique; the method was reviewed by Irish et al. (22E). Bewick, Pons, and coworkers made significant advances in the application of vibrational spectroscopy of electrode surface analysis. A sensitive technique of electrochemically modulated infrared spectroscopy was described by Bewick et al. (6E),and Pons et al. (36E) gave experimental consideration to Fourier transform infrared spectroscopy. Vo-Dinh et al. (51E) claimed to advance the quantitative application of SERS for determination of traces of organic compounds by adsorption onto submicrometer size silver-coated spheres deposited on filter paper. Finally, work by Engstrom (14E) is cited on the study of microscopic heterogeneity of solid electrode surfaces by observing the faradaic response resulting from ejection of extremely small quantities of a solution of an electroactive substance from a micropipet (1 pm i.d.) directly onto the surface. Two-dimensional mapping of surface activity was possible with 10-pm spot resolution.
F. CHEMICALLY MODIFIED ELECTRODES Activity in the area of chemically modified electrodes continues at a high level. The subject has recently been reviewed by Murray (55F). Further developments in theory (3F-5F, 8F)have facilitated understanding of redox mechanisms and the optimization of redox polymer film performance. Since it may be advantageous to use two contacting polymer films at the electrode, the transfer of electrons between such layers was studied (49I;1. To measure cross-reaction and polymer film permeability, microelectrodes and thin-layer cells were employed (26F, 280. Square wave voltammetry (64F),convolution voltammetry (48F),spectroelectrochemistry (30F),and EPR (2F,29F) have been used to characterize film redox properties. In the latter case ( 2 9 0 it was shown that Nafion impregnated with methylviologen (W+) yielded electron exchange rates on reduction suggestive of physical diffusion within the film. By contrast, when the sites are fixed in a film containing N,N’-bis[3-(trimethoxysilyl)propyl]-4,4’-bipyridine,the EPR signal was characteristic
of an immobilized site. Nafion films were extensively examined because of their stability and utility in entrapping positively charged metal complexes (6F, 14F) which may be used for electrocatalysis. Ferrocene immobilized in Nafion has been studied (610 and the possibility of using this system for the redox controlled release of anions has been demonstrated (25F). Polystyrenesulfonate films have also been examined (51F). It has been suggested that stable composite polyelectrolyte coatings with large ion exchange capacity and high cross coating charge propagation rates can be prepared (53F). Such a polymer might contain hydrophobic styrene groups and hydrophilic quaternized aminostyrenes, Bipyridine derivatives have also been extensively studied. These include 4,4’-dimonadecyl2,2’-bipyridine @IF), poly(methylvio1ogen) (SF),methylviologen (29F, 63F), and poly(xyly1 viologen) in Nafion films (63F),poly(cyanurvio1ogen)(41F),N,W-dialkyl-4,4’-bipyridine polymers (50F), and N-heptylviologen films deposited on silane modified tin oxide (17F). Polypyrrole (IOF, 13F), poly(bipyrazine) (16F) polyaniline (16F, 57F), poly(viny1pyridine) (31F, 62F), and poly(4,4’-dibrorno-4’’-vinyltriphenylamine) (54F). Films containing anthraquinone (22F, 36F), and napthoquinone ( 5 9 0 functionalities have been reported. Mechanistic studies of TCNQ modified electrodes (39F,40F),thionine ( I F ) , and polythiophene (65F) have been carried out. Because of their potential for the catalysis of dioxygen reduction, the immobilization of metalloporphyrins (7F,38F, 47F, 66F, 72F) and phthalocyanines (12F,58F) has also has been popular. Phthalocyanine films have also been used for photoelectrochemical studies (46F,52F). Ferrocene has been attached to a Pt electrode (378‘). Dispersions of metal and metal oxide microparticles on electrode surfaces have also been used for electrocatalysis (9F, 23F, 43F, 71F). It has long been recognized that the preconditioning or pretreatment of an electrode can have a dramatic effect on the electron transfer properties of solution substrates. Nonetheless, methods of activation are needed that are simple, rapid, and reproducible. Polishing (42F, 44F) and vacuum heat treatment (27F) of glassy carbon electrodes has been examined and methods for improving electrochemical reversibility reviewed (75F). Properties of graphite epoxy surfaces have been evaluated (24F). In situ conditioning techniques have included the use of a multistep 0.5-2 Hz wave form (119 and laser cleaning and activation (35F). The use of chemically modified electrodes for analytical purposes is becoming more frequent. Two major advantages might be realized: selective determination of species that are electroinactive or poorly behaved electrochemically and/or the selective concentration (extraction) of components into a film on the electrode so that the advantages of conventional stripping analysis can be realized not only for metals but for organic molecules as well. Polta and Johnson (60F) have exploited the influence of electroinactive adsorbates such as C1- and CN- on platinum oxide formation as the basis for flow injection analysis determination while the oxidation of a Ag(I)/Mo(CN),4- deposit is used as a basis for the determination of potassium (189. The electrocatalytic oxidation of As(II1) has also been examined (15F, 19F). An anion selective interface was prepared from a Pt electrode modified with 4-(/3-trimethoxysilyl)ethylpyridine ( 3 4 9 . It has been suggested (32F, 74F) that a film consisting of a redox center and a metal coordination site may be used for analysis. The voltammetric analysis step converts the metal into an oxidation state where coordination is not favorable, thus resulting in release. A nitrate sensor based on the chemisorption of iodine on a Pt electrode then coated with a layer of poly(viny1pyridine) has been reported (20F). The preparation of stable and reproducible films remains a problem. The adsorption of organic molecules onto electrode surfaces ( 6 7 9 or their extraction into a carbon paste electrode (CPE) (SSF, 69F)appears promising. Detection limits of 2 pmol have been observed for the determination of cysteine derivatives using a CPE impregnated with cobalt phthalocyanine (33F). Wang and Hutchins (70F) have shown that the base hydrolysis of cellulose acetate coated electrodes opens up the pores in the film while still inhibiting electrode fouling by proteins. Improved performance is also observed for small molecules, which tend to form insoluble films. The combination of chemically modified electrode methodology with developments in the fabrication of microelectrodes ANALYTICAL CHEMISTRY, VOL. 58, NO. 5, APRIL 1986
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should also lead to significant developments in the near future including molecular electronics (45F, 7 3 0 .
G . ANALYTICAL VOLTAMMETRY The applications of differential pulse and stripping voltammetry have continued to expand, with many new electrochemical techniques being applied to analytical measurements. For example, the effect of surface active compounds on the heterogeneous rate constant, k,, can have significant effects on the analytical signal and has been the subject of many theoretical reports. Ivaska and Smith (22G)have used on-line fast Fourier transform to deconvolute the effect of k, from the anodic stripping voltammogram and applied this method to cadmium and zinc. The effect of organic (6G)and surface active compounds on anodic stripping voltammetry of mercury films (77G)and speciation studies (29G)also has been reported. The small size of microelectrodes results in many advantages that have been discussed in this and previous reviews. A significant disadvantage has been the low current level. To overcome this problem, a lithographically produced array of linear gold and platinum microelectrodes has been constructed, which appears to give the advantages of a microelectrode (use of little or no supporting electrolyte, radical diffusion, etc.) a t a relatively high current level (62G). The differential anodic stripping voltammetry of mercury with gold film microelectrodes has been studied (6IG). There are a number of reports using square wave polarography with microdisk electrodes (52G), anodic stripping voltammetry (10G),and comparison of the ac and square wave response for irreversible and nearly irreversible systems (23G). Square wave polarography was also used for anodic stripping voltammetry in the presence of dissolved oxygen (80G)and the amperometric monitoring of reaction rates with a half-life down to 5 ms ( I I G ) . Many studies and variations of the mercury film electrodes have been reported, several of which were focused on the characteristics of the electrode. Gunasingham et al. (16G) described computer automation of anodic stripping voltammetry with a mercury film wall jet electrode. Stripping voltammograms with (78G) and without (20G) the use of semidifferentiation at thin mercury film electrodes were reported. Anodic stripping voltammetry a t carbon fiber (53G) and chemically modified glassy carbon electrodes (36G)was described. The optimization and comparison of four mercury electrodes for speciation studies were examined ( B G ) ,as were dry ashing methods for the anodic stripping voltammetric determination of cadmium and lead in biological materials (2G). A long-lasting dropping mercury electrode in anodic stripping voltammetry was the focus of two reports (33G,45G), while a third dealt with a modified standard addition Calibration (79G). The use of voltammetric methods to quantitate and characterize drugs, pesticides, herbicides, and related compounds has continued. Differential pulse polarography was used to study the hydrolysis of diazepam and oxazepam in acid media (81G). The electrochemical characterization of the diphenyl ether herbicide, nitrofen, was also reported (42G). Methods for the determination of a carbamate insecticide in soil samples (I7G),mitomycin C in human blood plasma and urine (64G), platinum in cis-dichlorodiammineplatinum(I1)-DNA complexes (73G),trichothecene mycotoxins (71G), and alcohol dehydrogenase activity (60G) by differential pulse polarography were reported. The use of adsorption stripping voltammetry of sex hormones (75G), some triazine and nitro group containin pesticides (4G),riboflavin (5IG),and some nucleotides (268)was described. Differential pulse voltammetry was used also as an in situ monitoring technique for the thermal decomposition kinetics of nitrate melts, being able to detect down to 10 ppb nitrite in fused alkali metal nitrates (44G),and to study the degradation of synthetic food colorings with and without ascorbic acid (14G). One of the mixed blessings of electroanalytical techniques has been their ability to monitor the different chemical forms of a given element. While this often creates difficulties in an analysis, this also generates a unique opportunity to determine the distribution of an element in solution. Such speciation studies have been the focus of a number of recent reports. Kramer et al. (27G)provided some cautions in the sampling, storage, and sample treatment for speciation studies in natural 40R
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waters. A voltammetric method for distinguishing between dissolved and particulate lead in the presence of hydrous oxides was reported (15G),as was the determination of trace heavy metals associated with suspended particulates in pond water (37G). The interaction of dissolved trace metals with humic substances isolated from marine and estaurine sediments was studied (47G). The determination of the complexing capacity and conditional stability constants of copper(I1) complexes with natural organic ligands in seawater by cathodic stripping voltammetry of the copper-catechol complex was reported (66G). Speciation studies of cadmium with L-aspartic acid in seawater (59G)and plutonium (32G)were described. The indirect trace determination of NTA in natural waters by differential pulse anodic stripping voltammetry was develoDed (72G). Theapplications of anodic stripping voltammetry continue to expand. Bond and Reust (5G) described a simple pretreatment of urine for lead determinations. Smart and Stewart used a 1000 molecular weight cutoff dialysis membrane to cover a rotated mercury film electrode to determine cadmium in the absence (58G) and presence (55G) of organic compounds. Acetonitrile (39G) and propylene carbonate (40G) were used in salting-out extractions for the analysis of antimony(III), indium(III), and cadmium(I1). Subtractive anodic Stripping voltammetry was used with flow injection analysis (74G). The coupling of electrocatalysis with anodic stripping voltammetry for the determination of trace copper was reported by Reignier and Buess (48G). The elimination of memory effect in trace heavy metal determinations in seawater (9G),and of iron interferences in copper determinations (8G), was described. Anodic stripping voltammetry was used to determine rhenium with an amalgamated rotating gold electrode (50G),platinum with a glassy carbon electrode (30G), bismuth in blood serum and urine (3G), and antimony in gunshot residue (7G). The range of elements that are accessible by cathodic stripping voltammetry continues to expand. In particular, a number of metals that have normally been studied by anodic stripping voltammetry can also be determined by cathodic stripping voltammetry using the appropriate complexes and with adsorptive collection. Namely, copper (65G),zinc (67G), and iron (70G) have been determined in this manner. Catechol complexes of copper (65G)and uranium(V1) (69G)have been used for trace analysis of seawater. The direct cathodic stripping voltammetric determination of dissolved vanadium in seawater was also reported (68G). Arsenic in biological samples (43G)and selenium in blood serum (18G,54G) have been determined. Gaseous hydrogen sulfide has been measured by cathodic stripping voltammetry after preconcentration on a silver metalized porous membrane electrode (41G). Thioamides have been determined by use of a rotating silver disk electrode followed by stripping analysis (24G). The applications of differential pulse voltammetry to a number of analytical determinations have been recently described. Multielement determinations in biological materials have been reported (1G). Thallium and related toxic metals have been determined by using a new modified electrode (25G). Differential pulse determinations of heavy metals (56G) and hydropyrolysis products (63G) in coal were reported. Trace sulfur in gasoline (46G), formaldehyde (13G), and bromine and iodine (I9G) were determined by differential pulse voltammetry. A number of interesting reports have appeared recently in the area of in vivo monitoring of electroactive compounds. Rice et al. used a simultaneous voltammetric and chemical monitor of dopamine release to verify the accuracy of the electrochemical response (49G). New electrochemical techniques for in vivo monitoring include a fast differential pulse amperometric method for the determination of dopamine ( 5 nM) in the presence of a 1OOO- to 4000-fold excess of ascorbate (34G). A double scan high speed voltammetric method for ascorbate took advantage of the chemical irreversibility of ascorbate oxidation (57G). A long voltammetric microelectrode (45 cm long) was used for the in vivo monitoring of acetaminophen in primates (76G). Differential pulse voltammetry was used to simultaneously monitor ascorbic acid, catechols, and 5-hydroxyindoles in rats (12G, 21G). In vivo voltammetry was used to detect and identify a compound that was not thought to be present in rat caudate, uric acid (38G), and this method has also been applied to a drug used in
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aggression research, fluprazine (35G).
H. CHARACTERIZATION OF REDOX SYSTEMS The effect of solvent and molecular structure on the kinetics of the electron transfer process was addressed by many researchers. Hupp et al. (32H,34H) examined the prediction of electron transfer reactivities from contemporary theory and compared it with experimental values. The electron tunneling distance for some outer-sphere chromium(II1) reductions was calculated (33H), as was the role of solvent reorganization dynamics in the electron transfer process for iron, cobalt, and manganese metallocenes in eight solvents at a mercury electrode (26H). The effect of mercury, gallium, lead, and thallium surfaces on outer sphere chromium(II1) reduction kinetics was also examined (57H). Geiger et al. studied the structural changes of metal clusters that occurred upon reductions. Such changes included bending of a nitrosyl group during the one-electron reduction of cyclopentadienyl metal nitrosyl compounds (25H), electrochemical changes in hapticity in mixed-sandwich iridium and rhodium compounds ( I 1H), and two-electron reduction with structural changes of a hexaosmium carbonyl cluster (76H). Further studies on electron transfer reactions and conformational changes associated with the reduction of bianthrones were reported (60H, 61H). Rather than just examining the structural changes upon electron transfers, Gustowski et al. (29H) and Wolf and Cooper (80H)designed molecules that undergo specific changes upon reduction; namely, they contain cation binding sites such as crown ethers that have a much higher affinity to a specific ion in the reduced form, as compared to the oxidized form. Steric effects in electron transfer reactions were studied by Koval and Ketterer (44H), while sterically hindered iron-sulfur clusters were used to successfuly model for the first time high potential ferredoxins (66H, 77“). The large k, value for copper(I1)dithiooxalate oxidation was used to identify a facile, light-activated cleavage of the C-C dithiooxalate bond after oxidation (38H). The effect of solvent (41H),viscosity (8123, and pH (21H) on heterogeneous electron transfer rate constants was examined. Interesting, the first report (41H) concluded that the k, changes were related to viscosity changes. A generalized model of electrode processes in mixed aqueous solvents was given by Maksymiuk et al. (59H). Temperature effects on 9,lO-diphenylanthracene reduction were examined by Svaan and Parker (72H). Ulstrup (78H) studied the temperature dependence of the transfer coefficient in electron and atom group-transfer processes. The electron transfer kinetics of quinones at glassy carbon, gold, and platinum from 170 to 298 K were reported (65H). Electrochemistry in micelles was the subject of two reports (27H, 39H). Electrochemical studies were performed in near-critical and supercritical ammonia by Crooks et al. (20H). Bipyridine and phenanthroline complexes of osmium, ruthenium, and iron were examined in liquid sulfur dioxide (24H). The first direct determination of the E l j zof benzene was reported by Mortensen and Heinze (63H),as was the formation of an organic tetraanion of acepleiadylene (64H) a t -3.14 V. Microelectrodes were used without a supporting electrolyte to oxidize short chain alkanes such as methane and butane (12H). Electrochemically induced reactions were the subject of several reports by Amatore et al. (4H, 6H). These included a report on absolute reactivities of phenyl derivatives in liquid ammonia (4H), and the competition with homogeneous electron transfer in noncatalytic systems (6H). The electrochemical initiation of aromatic SRNlreactions using redox catalysts was studied by Swartz and Stenzel (73“). The relationship between reduction potentials and anion radical cleavage rates in aromatic molecules was studied by Andrieux et al. (7H).The nucleophilic substitution of alkyl monohalides by electrogenerated polysulfide ions, S3--and SS2-,also was reported (68H). The electrochemistry of models for the active sites of redox proteins continued to be a fertile area of electrochemical research. The redox chemistry of copper(I1) thiolate and thioether complexes was reported ( I H ) , along with their relationship to certain copper proteins. Dicopper(I1) complexes of a large polyazacycloalkane (9H),triketonates (55H),phenoxo-bridged (62H),and N,S-macrocycles (2H) were studied. The electrocatalytic reduction of oxo anions by aqueous
molybdenum catechol complexes was examined (45H). Schultz et al. (70“) studied the electrochemistry of the iron-molybdenum cofactor isolated from Azotobacter uinelandii nitrogenase, as well as a dinuclear molybdenum cluster that undergoes a two-electron reduction (82H). The electrochemistry of an iron-molybdenum-sulfur cluster was reported by Coucouvanis et al. (18H). The binding and electrochemistry of molybdenum and tungsten complexes of dinitrogen were reported (35H),as well as the electrosynthesis of dinitrogen, hydride, isocyanide, and carbonyl complexes of molybdenum (3H). The area of redox protein model compounds that is by far the most prolific is porphyrin model complexes. One of the interesting aspects of this area is the ability to generate unusual oxidation states by variation of ligand structure (16H). High iron oxidation states were generated by the use of hydroxide and methoxide axial ligands (48H). The redox chemistry of these complexes was also studied by Lexa et al., using protected iron(I1) and iron(II1) porphyrins (52H)as well as the ligand exchange kinetics (53H). High, low, and variable-spin states of five-coordinate aryl iron(II1) porphyrins were synthesized and characterized (28H). Goff has shown an elegant method of using NMR to characterize products of electrochemical processes. Instead of deuterated solvents and electrolytes beinF used, the electroactive compound was deuterated, and H NMR was used (IOH, 31“). In many cases, this is quite simple and can be done directly on coulometry solutions at the millimolar level. In the latter report, low valent iron(1) and iron(0) porphyrin complexes were studied. The migration of a cr-bonded aryl substituent from iron to nitrogen upon oxidation was studied by Lancon et al. (46H). The fixation of carbon monoxide by iron(1) was examined (19H), as were molecular environment effects in “basket handle” and “picket fence” porphyrins (50H, 51H). Mixed valence complexes of dicobalt porphyrins were observed (49H), as was the catalytic reduction of dioxygen by cofacial cobalt porphyrins (13H, 56H). The electrochemistries of a physiologically active chlorin (30H),nickel ( 1 4 H ) , and iron (69H) chlorins were studied. There were a number of reports recently on the electrochemistry of technetium compounds. The electrochemistry and spectroelectrochemistry of technetium(II1)-phosphine complexes were reported (36H, 37H). The spectroelectrochemistry of the technetium(IV)/technetium(III) couple in bicarbonate solutions was examined (67H), as was the reduction of pertechnetate at carbon electrodes in aqueous noncomplexing acid media (47H). There was a report on the tentative correlation between the electrochemical oxidation of neuroleptics and their pharmacological properties ( 4 3 3 . The indirect reduction of materials that do not exchange electrons at the electrode surface was the subject of several reports with special emphasis on carbon dioxide. Carbon dioxide was catalytically reduced at cobalt phthalocyanine modified carbon electrodes (54H) with a rhodium complex (71H) and at an illuminated p-type semiconductor electrode (74H). Alcohols were oxidized by an electrogenerated ruthenium catalyst (23H),while allyl alcohols were indirectly reduced in the presence of iodide (58H). Ultrasound was used to increase the rate of the electrocatalytic dechloronation of polychloronated biphenyls (17H). The electrocatalytic reduction of a double Fe4S4cluster ferredoxin by methylviologen was studied (22H). The adsorption of carbon monoxide on a porous platinum electrode was studied by differential electrochemistry mass spectrometry (DEMS) (79H). The combination of e ectrochemistry and mass spectrometry also was used to study the oxidation of hydroxylamine (42H) and coals (75H). Hydrogen and carbon isotopes were used to study the exchange current densities on palladium of the bicarbonate/formate redox couple (15N). The electrochemical reduction of chromium(O), molybdenum(O), and tungsten(0) complexes were examined (40H). Voltammetry was used to evaluate the acidities of Bronsted acids in aprotic solvents (8H).
1
I. BIOELECTROCHEMISTRY It has now been over 5 years since the first examples of reversible heterogeneous electron transfer of proteins were presented. Rapid electron transfer makes possible the coupling of biospecific redox processes so that the electrode becomes a selective electron source or sink. Electron transfer ANALYTICAL CHEMISTRY, VOL. 58, NO. 5, APRIL 1986
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may be facilitated by the use of mediators, typically small molecules that may be soluble or immobilized on the electrode. These species should yield rapid and reversible reactions both with the electrode and with the protein. Cass and co-workers (211) have evaluated the ferricinium ion as a mediator for oxidoreductases. It is important to choose mediators that react rapidly with the protein of interest but not with other endogenous species. Redox polymer films have also been employed to catalyze such reactions (221). Considerable recent interest has focused on electrode modifiers, electroinactive species that alter the electrode/solution interface, and the nature of the interaction between the protein and the electrode. Such modifiers appear to facilitate rapid and reversible adsorption of the protein at the interface through hydrogen bonding and formation of salt bridges. Allen and co-workers (61)have studied a series of bifunctional modifiers for the enhancement of cytochrome c electron transfer. Hill and co-workers (321) have observed that (pyridinylmethylethy1ene)hydrazinecarbothioamide (PMHC) functions effectively for electron transfer enhancement of both negatively and positively charged proteins. Taniguchi et al. (631)have examined by SERS the interaction of cytochrome c with a Ag electrode using bis(Cpyridy1) disulfide as a modifier. Several groups (141,481,571) have reported on the importance of electrode treatment and ionic strength (141)on the heterogeneous electron transfer rates. Addition of a divalent cation (Mg”) has been shown to significantly enhance electron transfer for negatively charged proteins such as plastocyanin (71).Direct protein electron transfer has been used to catalyze dioxygen reduction (fungal laccase A) (491),coupling to photosystem I (cytochrome c ) (331),and as a CO sensor (pseudomonas thermocmboxydovorans) (671).In 1980,Kulys and co-workers (471)reported on the use of a conducting salt formed from the N-methylphenazinium (NMP)+cation and the tetracyanoquinodimethaneanion (TCNQ-) as an electrode material for facilitating electron transfer of glucose oxidase. This enzyme is of significant analytical importance because it catalyzes the oxidation of glucose normally using oxygen as a cosubstrate. Use of an electrode as the “cosubstrate” would be quite advantageous especially for an implantable sensor because the oxygen supply and therefore the electrode response are often variable. Recently, Albery et al. (51) have extended this work to include conducting salts of tetrathiafulvalene and quinoline with TCNQ. They report heterogeneous electron transfer rates of greater than cm s-* and electrodes that are stable for at least a month. It is argued that the electron transfer is direct rather than mediated as previously suggested (471). The use of enzymatic reactions (301)with electrochemical detection as the basis for biosensors continues to be an active area of research. Because of its importance in the development of the “artificial pancreas”, implantable glucose sensors have been the focus of considerable attention. Recent theoretical treatments (41,501)have dealt with the importance of oxygen as a cosubstrate. Other studies (91) have emphasized characteristics of amperometric sensor transient response. Cass and co-workers (201)have introduced a sensor in which enzyme oxidation is mediated by ferrocene derivatives, thus avoiding the problem of oxygen flux. Alternative mediators have been suggested (361,371,611). Gough et al. (291) have presented a new electrode design and a chemically modified reticulated vitreous carbon electrode with immobilized enzyme has been used as a detector for flow injection analysis of glucose (701).Two implantable sensors have been described (11,600and although results are encouraging, stability of such sensors beyond several hours or days remains a problem. Enzyme electrodes have been developed for the monitoring of L-lactate (511,521,661). Bienzyme systems have also proven useful for eliminating interferences (594 or for sequential conversion into detectable species (121,411,421,561). Tissue slices have been used for sensors and Schubert and co-workers (581) have developed a phosphate electrode based on the inhibition of acid phosphatase catalysis of glucose 6-phosphate hydrolysis. The use of whole microorganisms in detectors has been reviewed by Corcoran and Rechnitz (231).Biosensors based on pH changes detected potentiometrically with a FET have also been reported (161,171). Improved spatial and temporal resolutions have been two of the important recent goals in the development of in vivo electrochemistry. Albery and co-workers (31)have dealt 42R
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theoretically and experimentally with the question of what an in vivo electrode “sees” after implantation, particularly after several days. Fast cyclic voltammetry has proven useful not only to maintain a thin diffusion layer but also to provide additional electrochemical information about oxidation products (621). Several in vivo monitoring studies have been reported (461,681). The effective utilization of implanted electrodes is hampered by a lack of selectivity and deterioration of response as the electrode remains in contact with biological fluids for extended periods of time. In vitro selectivity studies for various electrodes have been performed (441). Selectivity may be further enhanced by coating the electrode with a charged membrane (Nafion), which tends to exclude anionic interferences (271). Selectivity coefficients for a Nafion membrane coated electrode have been measured (531).Microelectrodes continue to play an important role in in vivo electrochemistry and new geometries are being studied (451,641).A series of novel approaches to the electrochemically controlled release of biologically important molecules have been reported from Miller’s laboratory. Molecules immobilized a t or in a polymer film are released by electrochemical cleavage. Reduction of Co complexes has been employed for the release of glutamate and F-aminobutyic acid (711)).Timed release of species from polypyrrole (711)and 3-methoxythiophene films (111) has been reported. Because of its importance as a cofactor in over 300 enzyme-catalyzed redox reactions, NADH and NADPH electrochemistry continues to be of interest. This species is oxidized at a potential well above the reversible value and forms a film that fouls the indicating electrode. Gorton and coworkers (281) have reported that adsorption of meldola blue (7-(dimethylamino)-l,2-benzophenoxazine)on graphite yields mediated electron transfer through the formation of a charge transfer complex. Lowered oxidation potentials are observed. Several chemical and electrochemical oxidation studies of NADH have been reported with the objective of elucidating the mechanism of this process (101,181, 191, 431). The monitoring of NADH has been used to determine enzyme activity in biological fluids (SI). The sensitivity and selectivity of electrochemical detection have made it well suited for immunoassays. This subject has been recently reviewed (311,551).It has thus far not proven feasible to directly detect antibodies electrochemically; thus, it has been necessary to label the antibody or antigen (hapten) with an electroactivespecies (21). More commonly, the activity of an enzyme, measured by determining the concentration of an electroactive product released in solution, forms the basis for the enzyme immunoassay. Because every mole of enzyme can produce at least 103-104 mol of product, an amplification results. Sub-picomole detection is accordingly feasible. Assays for IgG (10 pg mL-’ detection limit) (694,hepatitis B surface antigen (131) and cq-acid glycoprotein (251) have been reported. Assays have exploited the steric inhibition, which results from the formation of an antibody-antigen complex. These include reconstitution of apoglucose oxidase (541)and electrochemically generated luminescence from pyrene-labeled human serum albumin (351). An in situ flow-through immunoreactor formed the basis for the measurement of the isoenzyme creatine kinase-MB (651) and the femtomole detection of IgG (241)by enzyme immunoassay. The latter assay can be performed with a precision and accuracy of *3% in less than 30 min. It would be desirable to locate the immunosorbent surface as close to the electrochemical sensor as possible. Most immunological reactions have such large equilibrium constants that it is difficult to displace the antibody-antigen complex once formed. Ikariyama and coworkers (341) have developed a clever system for displacement of the enzyme label from a membrane-covered electrode so that the high affinity reaction occurs in solution and not at the sensor surface. Although somewhat beyond the scope of this review, several electrochemical immunoassays based on potentiometric detection are noted here (151,261,381-401). Future developments in bioelectrochemistry will involve the application of microelectrode methodology and chemically modified electrodes to basic problems in neurochemistry, biology, and clinical chemistry.
J. SPECTROELECTROCHEMISTRY The range and capabilities of spectroelectrochemical methods continued to expand over the past 2 years. The
DYNAMIC ELECTROCHEMISTRY
combination of EXAFS with thin-layer electrochemistry (%J, 2 6 4 added another spectroscopic technique to the field of spectroelectrochemistry. Vibrational spectroscopic methods, because of their ability to provide direct structural information, have received growing interest in spite of their experimental difficulties. Pons et al. reported on the use of in situ infrared spectroelectrochemistry (11 4 to study adsorbed tetracyanoethylene anions at a platinum surface (164, the ferrocyanide/ferricyanidecouple (154, and anodic processes in thiocyanate solutions (64 using Fourier transform infrared spectroscopy. The ability to experimentally differentiate between bulk and adsorbed species should make this method quite attractive for many researchers. Raman spectroelectrochemistry was applied to the photooxidation of tetrathiafulvalene (285)and anodic reactions of platinum electrodes in halide solutions (144. The combination of spectrofluorescence with electrochemistry (spectrofluorovoltammetry) was used to study the formation of passivating films on electrodes (204. Luminescence spectroelectrochemistry of osmium(II/III) bipyridine complexes in thin cells was studied by Jones and Faulkner (104. Photolysis concurrent with the catalytic reduction of 4-chlorobiphenyl by electrogenerated anthracene radical anions was found to increase the homogeneous rate constant by an order of magnitude of which only 4% could be ascribed to convection (234. A rotating photoelectrode was used to detect organo-iron complex intermediates (14. Significant efforts were directed toward developing more sensitive techniques or to make the measurements in shorter periods of time. Robinson and McCreery significantly reduced the response time of the method by using smaller electrodes (50-400 pm) and by charge injection. The response time was on the order of 40 ns with agreement with theory from 150 ns to 100 ms. This technique was used to study the oxidation of dopamine by electrogenerated chloropromazine (194. A high sensitivity spectroelectrochemical method based on electrochemical modulation of an adsorbing analyte was also described (94.Increased sensitivity was also obtained by a hole in glassy carbon or graphite electrodes, which created a long path length thin-layer cell (184. A different long optical path length thin-layer cell was used to quantitate adsorbed aromatic molecules at platinum (74. The theory for the spectroelectrochemical response of a system with product deposition was presented (294. A spectroelectrochemicalcell was also designed with adjustable solution layer thickness (174. Several designs for thin-layer spectroelectrochemical cells have been reported recently (22J, 13J,54. The apparatus of Lin and Kadish (135) showed the advantages of Tefzel as a sealing material to be used in nonaqueous solvents. A filar electrode, using twin interdigitated electrodes, was reported (214. A multipass apparatus for molten salt spectroelectrochemistry was described by Harward et al. (84. One of the earliest spectroelectrochemical methods, EPR, is still the subject of much research. A new flow-through “bubble” electrode, combined with EPR, was described (274. The theory for EPR spectroelectrochemistry was studied by Compton et al. for fiisborder kinetics (45) and ECE vs. DISPI (24. EPR spectroelectrochemistry was applied to the reduction of 2-nitropropane ( 3 4 and anthraquinone (245) and the oxidation of 3,3’-dimethylnaphthidine(124;the last report also included visible spectroelectrochemistry.
K. INSTRUMENTATION A few descriptions of improvements in instrumentation and apparatus are cited. An earlier, informative text on electronics by Brown, Franz, and Moraff was brought to light by a review in J.Electroanal. Chem. (2K). Excellent discussions are found in volume 8 of “Comprehensive Treatise of Electrochemistry”, related to analog circuitry, by McKubre and Macdonald (5K), and computerization in electroanalytical chemistry, by Ridgeway and Mark (7K). Development of a microprocessor-based instrument interfaced to a microcomputer system was described by Bond, Greenhill, Heritage and Reust (1K) for differential-pulse stripping voltammetry. Cunningham and Freiser (3K) described a computer-controlled apparatus for the study of phenomena at the interface of two immiscible electrolyte solutions. Reardon, O’Brien, and Sturrock (6K) described a computer-controlled instrument for fast-sweep, square wave voltammetry in flow-through detectors. The use of positive feedback for compensation of the iR-drop in normal
pulse polarography was discussed by Hara (4K). Finally, Yarnitsky (8K) described an automated polarographic cell for increasing analytical throughput.
ACKNOWLEDGMENT We thank Linda Olson for her assistance in preparation of the manuscript. This work was supported in part by National Science Foundation Grant CHE-8312032 (D.C.J.). LITERATURE CITED A. BOOKS AND REVIEWS
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* 43R
DYNAMIC ELECTROCHEMISTRY perimental Techniques"; Plenum Press: New York, 1984. 8. MASS TRANSFER
(16) Aoki, K.; Akimoto, K.; Tokuda, K.; Matsuda, H.; Osteryoung, J. J . Electroanal. Chem. 1984, 171,219-30; 1985, 182,281-94. (28) Aoki, K.; Honda, K.; Tokuda, K.; Matsuda, H. J . Electroanal. Chem. 1985, 182,267-79; 1985, 186,79-86. (38) Aoki, K.; Osteryoung, J. J . Nectroanal. Chem. 1984, 160, 335-9. (48) Austin, D. S.; Johnson, D. C.; Hines, T. G.; Berti, E. T. Anal. Chem. 1983, 55,2222-6. (58) Barz, F.; Bernstein, C.; Vielstich, W. "On the Investigation of Electrochemical Reactions by Application of Turbulent Hydrodynamics"; in "Advances in Electrochemistry and Electrochemical Engineering"; Gerischer, H., Tobias, C. W., Eds.; Wiley: New York, 1984; Vol. 13, pp 261-353. (68) Bond, A. M.; Fleischmann, M.; Robinson, J. J . Electroanal. Chem. 1984, 172, 11-25. (78) Bond, A. M.; Oldham, K. 8. J . Electroanal. Chem. 1983, 158, 193-215. (86) Camacho, L.; Avlla, J. L.; Heras, A. M.; Garcia-Blanco, F. J . Electroanal. Chem. 1985, 182, 169-72. (96) Ciszkowska, M.; Stojek, F. J . Nectroanal. Chem. 1985, 197,101-10. (106) Deslouis, C.; Tribollet, B. J . Electroanal. Chem. 1985, 185, 171-6. (118) Eddowes, M. J. J . Nectroanal. Chem. 1983, 159,1-22. (128) Epelboin, 1.; Gabrielli, C.; Keddum, M. "Nonsteady-state Techniques"; !I Yeager, E., Bockris, J. O'M.,Conway, B. E., Sarangapani, S.,Eds. Comprehensive Treatise of Electrochemistry. Vol. 9. Electrodics: Experimental Techniques"; Plenum Press: New York, 1984 Chapter 3, pp 61-175. (138) Filinovsky, V. Yu.; Pleskov, Yu. V. "Rotating Disc and Ring-Disc Techniques"; in Yeager, E.; Bockris, J. O'M.; Conway, B. E.; Sarangapani, S.,Eds. "Comprehensive Treatise of Electrochemistry. Vol. 9. ElectrodICs: Experimental Techniques"; Plenum Press: New York, 1984; Chapter 5, pp 293-352. (148) Galvez, J. Anal. Chem. 1985, 57,585-91. (156) Galvez, J.; Alcaraz, M. L. Anal. Chem. 1985, 57,2116-20. (168) Gottesfeld, S.; Feldberg, S. W. J. Electroanal. Chem. 1985, 194, 1-10, (178) Hempstead, M. R.; Oldham, K. B. J . Nectroanal. Chem. 1984, 162, 1-12. (18s) Howell, J. 0.; Wightman, R. M. Anal. Chem. 1984, 56,524-9. (196) Ikeuchi, H.; Sato, M.; Sato, G. P. J . Nectroanal. Chem. 1984, 162, 321-6. (208) Jan, C.-C.; McCreery, R. L.; Gamble, F. T. Anal. Chem. 1985, 57, 1763-5. (216) Kovach, P. M.; Caudill, W. L.; Peters, D. G.; Wightman, R. M. J . Electroanal. Chem. 1985, 185,285-95. (228) Levart, E. J . Electroanal. Chem. 1985, 187,247-63. (238) McLaughlin, B. D. J . Nectroanal. Chem. 1984, 172, 1-9. (248) O'Dea, J.; Wojciechowski, J.; Osteryoung, J. Anal. Chem. 1985, 57, 954-5. (258) Penczek, M.; Stojek, 2 . J . Electroanal. Chem. 1985, 191,91-100. (268) Pratt, K. W. Anal. Chem. 1984, 56, 1967-70. (278) Reller, H.; Kirowa-Eisner, E.; Gileadi, E. J . Electroanal. Chem. 1984, 161,247-68. (288) Rosamilia, J. M.; Miller, B. Anal. Chem. 1984, 56,2410-13. (298) Rosamilia, J. M.; Miller, B. J . Electroanal. Chem. 1984, 160,131-40. (308) Schuette, S. A.; McCreery, R. L. J . Nectroanal. Chem. 1985, 191, 329-42. (318) Shoup, D.; Szabo, A. J . Electroanal. Chem. 1984, 160,27-31. (328) Shoup, D.; Szabo, A. J . Electroanal. Chem. 1984, 160,1-17; 19-26. (338) Sleszynski, N.; Osteryoung, J. Anal. Chem. 1984, 56, 130-5. (348) Swathirajan, S.; Bruckenstein, S. J . Electroanal. Chem. 1984, 163, 77-92. (358) Thormann, W.; van den Bosch, P.; Bond, A. M. Anal. Chem. 1985, 57,2764-70. (368) Vernev, E.: Martin, J. R.; Clechet, P. J . flectroanal. Chem. 1985, . 132,2178-80. (376) Wehmeyer, K. R.; Wightman, R. M. Anal. Chem. 1985, 57, 1989-93. (388) Wehmeyer, K. R.; Deakin, M. R.; Wightman, R. M. Anal. Chem. 1985, 57, 1913-16. (398) Woodard. F. E.; Reilley. C. N. "Thin-Layer Cell Techniques", in Yeager, E., Bockrls, J. O'M., Conway, B. E., Sarangapani, S., Eds. "Comprehensive Treatlse of Electrochemistry. Vol. 9. Eiectrodics: Experimental Techniques"; Plenum Press: New York, 1984, Chapter 6, pp 353-92. C. FLOW-THROUGH DETECTORS
(1C) Albery. W. J. J . Hectroanal. Chem. 1985, 191,1-13. (2C) Albery, W. J.: Brett, C. M. A,: Brett, A. M. C. 0. Anal. Chem. Symp. Ser. 1984, 18 (F-t. A), 219-31. (3C) Albery, W. J.; Haggett, B. G. D.; Jones, C. P.; Pritchard, M. J.; Svanberg, L. R. J . Electroanal. Chem. 1985, 188,257-63. (4C) Albery, W. J.; Svanberg, L. R.; Wood, P. J . Electroanal. Chem. 1984, 162,45-53. (5C) Alexander, P. W.; Akapongkul, U. Anal. Chim. Acta 1984, 166, 119-27. (6C) Alexander, P. W.; Haddad, P. R.; Trojanowica, M. Anal. Chim. Acta 1985, 171, 151-63. (7C) Anderson, J. L.; Moldoveanu, S. J . Nectroanal. Chem. 1984, 179, 107- 17. (8C) Anderson, J. L.; Whiten, K. K.; Brewster, J. D.; Ou, T.-Y.; Nonidez, W. K. Anal. Chem. 1985, 57, 1366-73. (9C) Aoki, K.; Tokuda, K.; Matsuda, H. J . Electroanal. Chem. 1985, 195, 229-49. (1OC) Barnes, A. C.; Nleman, T. A. Anal. Chem. 1983, 55,2309-12.
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(11C) Cope, D. K.; Tailman, D. E. J . Nectroanal. Chern. 1985, 188,21-31. (12C) Curran, D. J.; Tougas, T. P. Anal. Chem. 1984, 56,672-8. (13C) Dalhuijsen, A. J.; van der Mew, Th. H.; Hoogendoorn, C. J.; van Bennekom, W. P. J . Nectroanal. Chem. 1985, 182,295-313. (14C) Elbicki, J. M.; Morgan, D. M.; Weber, S.G. Anal. Chem. 1984, 56, 978-95. (15C) Gunasingham, H. Anal. Chim. Acta 1984, 159,139-47. (16C) Gunasingham, H.; Fleet, B. Anal. Chem. 1983, 55, 1409-14. (17C) Gunasingham, H.; Tay, B. T.; Ang, K. P. Anal. Chlm. Acta 1985, 176, 143-50. (18C) Hitchman, M. L. Anal. Chim. Acta 1985, 171, 131-9. (19C) Hitchman, M. L.; Aziz, A.; Chlngakule, D. D. K.; Nyasulu, F. W. M. Anal. Chim. Acta 1985, 171, 141-50. (20C) Hitchman, M. L.; Nyasulu, F. W. M. Anal. Chim. Acta 1985, 173, 337-41. (21C) Knecht, L. A.; Guthrie, E. J.; Jorgenson, J. W. Anal. Chem. 1984, 56, 479-82. (22C) Kok, W. Th.; Brinkman, U. A. Th.; Frei, R. W. Anal. Chim. Acta 1984, 162, 19-32. (23C) Kowalski, 2.; Kubiak, W. Anal. Chlm. Acta 1984, 159,129-37. (24C) Lacourse, W. R.; Krull, I . S. Anal. Chem. 1985, 57, 1810-14. (25C) Lunte, C. E.; Kissinger, P. T.; Shoup, R. E. Anal. Chem. 1985, 57, 1541-6. (26C) Matson, W. R.; Langlais, P.; Volicer, L.; Gamache, P. H.; Bird, E.; Mark, K. A. Clin. Chem. 1984, 30, 1477-88. (27C) Moldoveanu, S.; Anderson, J. L. J. Electroanal. Chem. 1984, 175, 67-77. (28C) Moldoveanu, S.; Anderson, J. L. J . flectroanal. Chem. 1985, 185, 239-52. (29C) Moldoveanu, S.;Handler, G. S.; Anderson, J. L. J . Electroanal. Chem. 1984, 179,119-30. (30C) Reardon, P. A.; O'Brien, G. E.; Sturrock, P. E.; Anal. Chim. Acta 1984, 162, 175-87. (31C) Roosendaal, E. M. M.; Poppe, H. Anal. Chim. Acta 1984, 158, 323-33. (32C) Shih, Y. T.; Carr, P. W. Anal. Chim. Acta 1985, 167,137-44. (33C) Stulik, K.; PacEtkovEt, V. CRC Crit. Rev. Anal. Cbem. 1984, 14 (4), 297-35 1. (34C) Tougas, T. P.; Curran, D. J. Anal. Chlm. Acta 1984, 161,325-31. (35C) Tougas, T. P.; Jannetti, J. M.; Collier, W. G. Anal. Chem. 1985, 57, 1377-81. (36C) Wang, J.; Dewald, H. D. Anal. Chem. 1984, 56, 155-9. (37C) Wang, J.; Freiha, '6. A. J . Electroanal. Chem. 1984, 164,79-87. (38C) Wechter, C.; Sleszynski, N.; O'Dea, J. J.; Osteryoung, J. Anal. Chim. Acta 1985, 175,45-53. (39C) Wise, J. A.; Heineman, W. R.; Kissinger, P. T. Anal. Chim. Acta 1985, 172,1-12. D. HETEROGENEOUS/HOMOGENEOUSKINETICS
(1D) Amatore, C.; Capobianco, G.; Farnia, G.; Sandona, G.; Saveant, J. M.; Severin, M. G.; Vianello, E. J . Am. Chem. Soc. 1985, 107, 1815-24. (2D) Andrieux, C. P.; Hapiot, P.; Saveant, J. M. J . Nectroanal. Chem. 1984, 172,49-65. (3D) Aoki, K.; Tokuda, K.; Matsuda, H. J . Nectroanal. Chem. 1984, 160, 33-45. (4D) Atwell, R. J., Jr.; Sridharan, R.; DeLevie, R. J . Electroanal. Chem. 1985, 194, 143-8. (5D) Baecklund, P.; Nyhoim, L.; Wikmark, G. Anal. Chem. 1984, 56, 1209-14. (6D) Baranski, A. S.; Fawcett, W. R.; Gilbert, C. M. Anal. Chem. 1985, 57, 166-70. (7D) Bieniasz, L. J . Nectroanal. Chem. 1984, 170,77-87; 1985, 188, 13-20. (8D) Bond, A. M., Fleischmann, M.; Robinson, J. J . Electroanal. Chem. 1984, 172,11-25. (9D) Bond, A. M.; Fleischmann, M.; Robinson, J. J . Electroanal. Chem. 1984, 168,299-312. (10D) Bond, A. M.; Fleischmann, M.; Robinson, J. J . Electroanal. Chem. 1984, 180,257-63. (11D) Bond. A. M.; Henderson, T. L. E.; Oldham, K. B. J . Nectroanal. Chem. 1985, 791,75-90. (12D) i m Bontempelli, ~ ~G.: Magno, F.; Daniele, S. Anal. Chem. 1985, 57, (13Dj-Bus1, F.; D'Angelantonio, M.; Eettoli, G.; Concialinl, V.; Tubertini, 0.; Barker. G. C. Inorg. Chim. Acta 1984, 8 4 , 105-11. (14D) Brown, T. F.; Caster, D. M.; Brown, S. D. Anal. Chem. 1984, 56, 1214-21. (150) Camacho, L.; Avila, J. L.; Heras. A. M.; Garcia, 6. F. J . Electroanal. Chem. 1985, 182,173-8. (16D) Camacho, L.; Blazquez, M.; Jlmenez, M.; Dominquez, M. J . Electroanal. Chem. 1984, 172, 173-9. (17D) Chen, H. Y.; Neeb, R. Fresenius' 2.Anal. Chem. 1984, 319,240-7. (18D) Ciszkowski, M.; Stojek, Z.J . Electroanal. Chem. 1985, 191,101-10. (19D) Conti, P.; Marassi, R.; Misici, L. J . Electroanal. Chem. 1985, 184, 77-85. (20D) De Juan, M.; Heras, A. M.; Camacho, L.; Avlla, J. L.; Jimenez, C. J . Electroanal. Chem. 1985, 191,303-10. (21D) Eliason, R.; Parker, V. D. J . Electroanal. Chem. 1984, 165,21-7. (22D) Fatouros, N.; Chemla, M.; Amatore, C.; Saveant, J. M. J . Electroanal. Chem. 1984, 172,67-81. (23D) Feder, A. L.; Yarnitzky, C. Anal. Chem. 1984, 56,678-81. (24D) Fleischmann, M.; Lasserre, F.; Robinson, J.; Swan, D. J , Electroanal. Chem. 1984, 177,97-1 14, 115-27. (25D) Galvez, J. Anal. Chem. 1985, 57, 585-91. (26D) Galvez, J.; Seona, C.; Molina, A,; Van Leeuwen, H. P. J . Nectroanal. Chem. 1984, 167, 15-42.
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D Y N A M I C ELECTROCHEMISTRY (79H) Walter, 0.;Heitbaum, J. Ber. Bunsen-Ges. Phys. Chem. 1984, 88, 6-10. (80H) Wolf, R. E., Jr.; Cooper, S. R. J. Am. Chem. Soc. 1984, 106, 4646-7. (81H) Zhang, X.; Leddy, J.; Bard, A. J. J. Am. Chem. Soc. 1985, 107, 3719-21. (82H) Zhuang, B.; McDonald, J. W.; Schultz, F. A.; Newton, W. E. Organometalllcs 1984, 3 , 943-8.
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(511) Mascini, M.; Moscone, D.; Paileschi, G. Anal. Chim. Acta 1984, 157, 45-5 1. (521) Mascini, M.; Fortunati, S.;Moscone, D.; Palleschi, G.; MassCBenedetti, M.; Fabletti, P. Clin. Chem. 1985, 3 1 , 451-3. (531) Nagy, G.; Gerhardt, G. A.; Oke, A. F.; Rice, M. E.; Adams, R. N.; Moore, R. B.; Szentirmay, M. N.; Martin, C. R. J. Nectroanal. Chem. 1985, 188, 85-94. (541) Ngo, T. T.; Bovaird, J. H.; Lenhoff, H. M. Appl. Biochem. Biotech. 1985, 1 1 , 63-70. (551) North, J. R. U . K. Trends Blotechnol. 1985, 3 , 180-6. (561) Pan, C. P.; Rechnitz, G. A. Anal. Chim. Acta 1984, 160, 141-7. (571) Razumas, V. J.; Jasaitis, J. J.; Kulys, J. J. J. Bioelectrochem. Bloeng. 1984, 12, 297-322. (581) Schubert, F.; Renneberg, R.; Scheiler, F. W.; Kirstein, L. Anal. Chem. 1984, 56, 1677-82. (591) Schubert, F.; Kirstein, D.; Schroeder, K. L.; Scheller, F. W. Anal. Chlm. Acta 1985. 189, 391-6. (601) Schlchiri, M.; Kawamori, R.; Hakui, N.; Asakawa, N.; Yamasaki, Y.; Abe, H. Blomed. Blochim. Acta 1984, 43, 561-8. (611) Sonawot, H. M.; Phadke, R. W. S.;Govil, G. Biotechnol. Bioeng. 1984, 26, 1066-70. (621) Stamford, J. A.; Kruk, 2. L.; Millar, J.; Wightman, R. M. Neurosci. Left. 1984, 51, 133-6. (631) Taniguchi, I . ; Iseki, M.; Yamaguchi, H.; Yasukouchi, K. J. Nectroanal.’ Chem. 1984, 175, 341-8. (641) Thormann, W.; Vanden Bosch, P.; Bond, A. M. Anal. Chem. 1985, 5 7 , 2764-70. (651) Toyoda, T.; Kuan, S. S.;Guiibault, G. G. Anal. Chem. 1985, 5 7 , 2346-9. (661) Tsuchida, T.; Takasugi, H.; Yoda, K.; Takizawa, K.; Kobayashi, S.Blotechno/. Bioeng. 1985, 2 7 , 637-41. (671) Turner, A. P. F.; Aston, W. J.; Higgins, 1. J.; Bell, J. M.; Colby, J.; Davis, G.; Hill, H. A. 0. Anal. Chlm. Acta 1964, 163, 161-74. (681) Wang, J.; Hutchins, L. D.; Selim, S.;Cummings, L. 8. J . Bioelectrochem. Bloenerg. 1984, 12, 193-203. (691) Wehmeyer, K. R.; Halsall, H. B.; Heineman, W. R. Clin. Chem., in press. (701) Wieck, H. J.; Heider, G. H., Jr.; Yacynych, A. M. Anal. Chim. Acta 1984, 158, 137-41. (711) Zlnger, B.; Miller, L. L. J . Nectroanal. Chem. 1984, 181, 153-72. (721) Zlnger, 8.; Miller, L. L. J. Am. Chem. Soc. 1984, 106, 6861-3. J. SPECTROELECTROCHEMISTRY
(1J) Boyd, D. C.; Bohiing, D. A.; Mann, K. R. J. Am. Chem. Soc. 1985, 107, 1641-4. (2J) Compton, R. G.; Daly, P. J.; Umwin, P. R.; Waller, A. M. J. Nectroanal. Chem. 1985, 191, 15-29. (3J) Compton, R. G.; Page, D. J.; Seaiy, G. R. J. Nectroanal. Chem. 1984, 161. 129-45. -(4) Compton, R. G.; Page, D. J.; Seaiy, G. R. J. Nectroanal. Chem. 1984, 163. 65-75. -(5J) Condit, D. A.; Herrera, M. E.; Stankovich, M. T.; Curran, D. J. Anal. Chem. 1984, 56, 2909-14. (6J) Foley, J. K.; Pons, S.;Smith, J. J. Langmulr 1985, 1, 697-701. (7J) Gui, Y. P.; Porter, M. D.; Kuwana, T. Anal. Chem. 1985, 5 7 , 1474-6. (8J) Harward, B. L.; Klatt, K. N.; Mamantov, G. Anal. Chem. 1985, 5 7 , 1773-5. (9J) Jan, C. C.; Lavine, B. K.; McCreery, R. L. Anal. Chem. 1985, 5 7 , 752-8. (IOJ) Jones, E. T. T.; Fauikner, L. R . J. Nectroanal. Chem. 1984, 179, 53-64. (11J) Korzeniewskl, C.; Pons, S.J. Vac. Sci. Techno/.6 1985, 3 , 1421-4. (12J) Lapkowski, M.; Strojek, J. W. J. Nectroanal. Chem. 1985, 182, 3 15-33. (13J) Lin, X. Q.; Kadish, K. M. Anal. Chem. 1985, 5 7 , 1498-1501. (14J) Loo, B. H.; Lee, Y. G. Appl. Surf. Scl. 1984, 18, 345-60. (15J) Pons, S.;Datta, M.; McAleer, J. F.; Hinman, A. S. J. Electroanal. Chem. 1984, 160, 369-76. (16J) Pons, S.;Khoo, S. B.; Bewick, A,; Datta, M.; Smith, J. J.; Hinman, A. S.;Zackmann, G. J. Phys. Chem. 1984, 88, 3575-8. (17J) Porter, M. D.; Dong, S.;Gui, Y.; Kuwana, T. Anal. Chem. 1984, 56, 2263-5. (18J) Porter, M. D.; Kuwana, T. Anal. Chem. 1984, 5 6 , 529-35. (19J) Robinson, R. S.;McCreery, R. L. J. Nectroanal. Chem. 1985, 182, 61-72. (20J) Rublm, J. C.; Sala, 0.; Gutz, I. G. R. An. Simp. Bras. Netroqulm. Netroanal. 4th 1984, 29-35; 37-43. (21J) Sanderson, D. 0.; Anderson, L. D. Anal. Chern. 1985, 57, 2388-93. (22J) Scherson, D. A.; Saranjapani, S.;Urbach, F. L. Anal. Chem. 1985, 5 7 , 1501-3. (23J) Shukla, S.S.;Rusling, J. F. J. Phys. Chem. 1985, 89, 3353-8. (24J) Sieiro, C.; Sanchez, A.; Crouigneau, P. Spectrochlm. Acta, Part A 1984, 40A, 453-6. (25J) Smith, D. A.; Eider, R. C.; Helneman, W. R. Anal. Chem. 1985, 5 7 , 2361-5. (26J) Smith, D. A.; Heeg, M. J.; Heineman, W. R.; Elder, R . C. J. Am. Chem. SOC. 1084, 106, 3053-4. (27J) Stoesser, R.; Pragst, F.; Henrion, 0. 2.Chem. 1985, 25, 157. (28J) Van Duyne, R. P.; Haushalter, J. P. J. Phys. Chem. 1984, 88, 2446-5 1. (29J) Yap, W. T.; Blubaugh, E. A.; Durst, R. A,; Burke, R. T. J. Electroanal. Chem. 1984, 160, 73-8.
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K. INSTRUMENTATION
(IK) Bond, A. M.; Greenhill, H. B.; Heritage, I. D.; Reust, J. B. Anal. Chlm. Acta 1984, 165, 209-16.
Anal. Chem. 1986, 58,49 R-65 R 1. (6K) Reardon, P. A.; O’Brlen, G. E.; Sturrock, P. E. Anal. Chim. Acta 1084, 162, 175-87. (7K) Ridgway, T. H.; Mark, H. B., Jr. “Computerization in Electroanalytical Chemistry”; in White, R. E., Bockris, J. O’M., Conway, 8. E., Yeager, E., Eds. ”Comprehensive Treatise of Electrochemistry”; Plenum Press: New York, 1984; Vol. 8, Chapter 2. (8K) Yarnitsky, C. N. Anal. Chem. 1985, 57, 2011-15.
(2K) Brown, P. B.; Franz, G. N.; Moraff, H. “Electronics for the Modern Scientist”; Elsevier Biomedical Press: Amsterdam, 1982. Reviewed by Reeves, R. J. Electroanal. Chem. 1984, 161, 213-4. (3K) Cunningham, L.; Frelser, H. Larrgmuir 1085, 1, 537-41. (4K) Hara, M. Talanta 1985, 32, 41-3. (5K) McKubre. M. C. H.; Macdonald, D. D. “Instrumentation”; in White, R. E., Bockris, J. O’M., Conway, B. E., Yeager, E., Eds. “Comprehensive Treatise of Electrochemistry”; Plenum Press: New York, 1984; Vol. 8, Chapter
Nuclear and Radiochemical Analysis William D. Ehmann* and Steven W. Yates Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-0055
ative abstract in Chemical Abstracts (CA) can be cited. Laboratory or government reports and conference proceedings that may be difficult to obtain have generally been omitted. CA citations are appended to references where the language is other than English or where the publication is in a less accessible journal or report.
With this review, a change in authorship, title, and scope from a previous series of reviews in Analytical Chemistry under the title of “Nucleonics” is initiated. We feel the new title reflects an emphasis appropriate to this journal and the interests of many of its readers. In general, we have chosen to exclude articles in the areas of health physics, nuclear spectroscopy (unless directly related to analytical utility), nuclear engineering, fusion, radioactive waste disposal, fallout, and nuclear and particle physics. In contrast, topics clearly representing the use of nuclear properties for analysis are highlighted. Tor>icssuch as Darticle-induced X-ray emission (PIXE), plasma desorption mass spectrometry, radioimmunoassay, Mossbauer spectroscopy, and common radiotracer applications are now covered in reviews under other titles in this or other readily available journals. These latter research areas, although well populated by scientists trained in the fields of nuclear and radiochemistry, are treated briefly here. We cannot resist the temptation to comment on some topics not usually found in other reviews, but of general interest to nuclear and radiochemists. Included are topics such as neutrino research, discoveries of new elements, the search for decay of the proton, and new decay processes, even though they do not fit comfortably under the new title for this series. Along with many readers of the previous “Nucleonics” review series, we wish to express our gratitude to William Lyon and Harley Ross for their efforts to keep us up with the expanding literature of nuclear and radiochemical analysis. We hope that current readers will find this review useful and that not too many of your favorite topics will have been excluded. This review is based largely on a computerized keyword search of Chemical Abstracts for the period from mid-1983 to mid-November 1985. Approximately 50% of the nearly 2000 abstracts considered were found by searching with the keyphrase “radiochemical analysis”. Nuclear analytical chemistry is now clearly a mature field; breakthroughs in methodology are now rare, but innovative applications of nuclear techniques continue to increase. Some of the most interesting developments in the last few years have been the use of activatable (The term “activatable” is more commonly used in the radiochemical literature and will be used in the remainder of this review.) elemental or enriched isotope tracers in environmental studies, preirradiation derivatization or chemical separations to permit enhanced sensitivity or speciation, nuclear microprobe techniques, unique applications of prompt y neutron activation analysis, and accelerator-based dating methods that replace low activity counting methods. A complete review of applications is not possible within the editorial guidelines; however, we have chosen to include a few representative applications in each of a wide variety of scientific fields, and the reader should refer to our tabulation of more specialized reviews for sources of additional citations. Publications in less common languages are included in this review only where the material covered is not represented in a more widely used langu e. Publications in major scientific languages other than Enzish are included when an inform0003-2700/86/0358-49R$Og.50/ 0
A. BOOKS AND REVIEWS We have chosen to separate comprehensive books and other review papera from original research contributions. Table I contains a tabulation of selected reviews and books that may be of interest to many of our readers. The list is not exhaustive, but should provide starting points for further literature searches on specific topics. The appearance of a new book in the fields of nuclear and radioanalytical chemistry is a rarity. In the current review period three new books that should have broad appeal to researchers in nuclear and radioanalytical chemistry have been published. The first, entitled “Nuclear Analytical Chemistry” by Brune, Forkman, and Perrson (AI), provides an introduction to nuclear structure, decay processes, nuclear reactions, sources of particles and radiations interactions of radiation with matter, radiation detectors, nuclear electronics, and spectral analysis. In addition, approximately 200 of the 557 pages are devoted to the methodology of activation analysis and a review of its applications. Particle-induced X-ray emission (PIXE) and scattering techniques are only briefly mentioned. Unfortunately, very few of the references cited bear publication dates in the 1980s. This volume would serve well as a textbook for a course in radioanalytical chemistry at the college senior/first-year graduate student level or as an introduction to activation analysis for individuals trained in other disciplines. The second book is entitled “Neutron Activation Analysis for Clinical Trace Element Research, Vol. I and 11”by Heydorn (A2). In contrast to the previously mentioned book, this monograph is directed to a more advanced audience. The author is quite successful in bridging the gap between clinical and analytical scientists. This two-volume set contains many useful data tabulations and references. The third book entitled “Studies in Environmental Science, Vol. 22, Environmental Radioanalysis” by Das et al. (A3) provides a good introduction to activation analysis and PIXE as applied in the environmental field.
B. ACTIVATION ANALYSIS 1. Instrumental Thermal Neutron Activation Analysis
(INAA). In this section we cover the new developments in the methodology of INAA using reactor or isotopic neutron sources and selected applications. Publications combining neutron activation with postirradiation radiochemical separations of an element or group of elements (RNAA) are reviewed in Section B.7. One of the more interesting recent developments has been the use of elemental or enriched isotopic tracers along with INAA. Tsukada et al. ( B I ) have used enriched stable l16Cd @
1986 American Chemical Society
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