REPORT
in Behavior of,
MICROELECTRODES Stanley Pons Department of Chemistry University of Utah Salt Lake City, Utah 84112
Martin Fleischmann Department of Chemistry University of Southampton Southampton S09 5NH England
In the early 1970s a number of research groups exploited the advantages of microelectrodes, which are normally de fined as devices with characteristic di mensions smaller than about 20 μπι, over conventional electrodes. Because many of the undesirable aspects of electrochemical and electroanalytical techniques can be reduced or eliminat ed with microelectrodes, their use has grown rapidly. Microelectrodes are advantageous for several reasons. First, very small currents (rates of reaction) as low as ~ 1 0 - 1 7 A, 10 e - /s, can be measured with relative ease. Second, iR losses in solution are reduced at small elec trodes. This "error" to the applied po tential at the electrode-solution inter face prevents electrochemical experi ments from being performed with "large" electrodes in all but ionically conducting solutions. Third, capacitative charging currents, the limiting fac tor in all transient electrochemical techniques, are reduced to insignifi cant proportions at electrodes of suffi ciently small area. Fourth, the rate of mass transport to and from the elec trodes increases as the electrode size decreases; moreover, steady states of mass transfer are rapidly established. As a consequence of reduced capacitative charging currents and increased mass transport rates, microelectrodes exhibit excellent signal-to-noise (S/N) characteristics. Finally, as the litera ture indicates, microelectrode systems are easily implemented and involve rel atively low costs. The unusual properties of microelec trodes also allow electrochemical mea surements to be made on novel sys tems—those that are not amenable to 0003-2700/87/A359-1391/$01.50/0 © 1987 American Chemical Society
Anodic reaction
Cathodic reaction
Figure 1. Designs of microelectrodes. (a) Side view of a microdisk electrode, (b) plane view of a microring electrode, (c) plane view of a microdisk-microring electrode, (d) side view of a spherical mercury drop deposited on a disk, (e) side view of a particle in a dispersion undergoing electrolysis by a field applied across the cell. ANALYTICAL CHEMISTRY, VOL. 59, NO. 24, DECEMBER 15, 1987 · 1391 A
tography. The detector in the gas phase is especially sensitive for analytes that have a proton loss involved in chemical reactions following the electron trans fer. The increased sensitivity results from the high mobility of the proton. The detectors are species-sensitive be cause of differences in standard poten tials of the analytes, and they are quan titatively more sensitive than thermal conductivity detectors. The problem of the analysis of mass transport to finite disks and rings
Potential/Volts vs. Ag/Ag+ Figure 2. Effect of electrolyte addition to acetonitrile when using a platinum disk microelectrode of radius 0.5 μνη in oxidation of 1 mM ferrocene. (a) Without electrolyte, (b) with 1 mM Et4NCI04.
conventional electroanalysis. In this R E P O R T we will review some of these systems and comment on some of the more interesting properties of very small electrodes, their application to other types of analytical and physical measurements, and solutions to the problem of mass transport to certain microelectrode geometries. Further in formation about these areas is avail able; see the Suggested Reading list. Figure 1 illustrates some of the de signs of microelectrodes. The high mass transfer rates allow electroanalytical measurements to be made at low substrate concentrations (using the chronoamperometric or chronopotentiometric responses as well as stripping voltammetry of preconcentrated spe cies, e.g., using Hg microdrops). Other applications include the measurement of the kinetics of fast electrode reac tions (from the kinetically controlled polarization curves) and of the kinetics of fast reactions in solution coupled to electrode reactions (e.g., using the radi us dependence of the limiting currents that become kinetically controlled by the reactions in solution). These appli cations are dependent on three of the special properties because of the spher ical (or quasi-spherical) concentration and potential fields surrounding the microelectrode: the reduction of iR losses, decreased capacitative currents, and increased mass transport rates. The reduced iR effect is particularly important to other applications of mi croelectrodes because it allows mea surements to be made on novel systems under unusual conditions such as the following: • nonpolar solvents in the presence of appropriate support electrolytes (type 1) • polar solvents and mixtures of po lar and nonpolar solvents in the ab sence of purposely added support elec
trolytes (type 2, Figure 2a), • low-temperature glasses and eutectics (type 3, Figure 2b), and • the gas phase (type 4). Measurements of the first three types have been made with convention al microdisk electrodes (Figure la). Type 2 measurements have also been demonstrated using the bipolar elec trolysis of dispersions of metal and semiconductor particles supported in solvents without added support elec trolyte (Figure le). It is important that ions be invariably generated (or con sumed) in electrode reactions, that is Ox + e " f i Rd~ or +
Ox + e" *t Rd so that conditions can be chosen to in crease the conductance of the solution in the vicinity of the microelectrodes. Because the bulk of the resistance is in this region (the resistance is propor tional to the resistivity and the inverse of the electrode radius), the ohmic losses are small and calculable or mea surable, particularly in the kinetically controlled region of the polarization curves. Measurements in the gas phase (type 4) are now made with disk-ring electrodes (Figure lc) where the cur rent will usually, but not necessarily, flow over the "insulator" surface sepa rating the disk from the surrounding ring electrode while gas-phase species diffuse to the microdisk or, most likely, to the edges of the disk through the quasi-spherical diffusion field. The conditions are therefore somewhat dif ferent from those for measurements of types 1, 2, and 3. We have previously demonstrated the utility of these devices as sensitive detectors in gas-phase chromatogra phy and for measurements of picogram levels of DNA bases by liquid chroma-
1392 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 24, DECEMBER 15, 1987
It is well known that closed-form sim ple solutions can be obtained for most types of electrochemical experiments using hemispherical or spherical micro electrodes, provided that any coupled reaction kinetic terms are first order or pseudo first order. For a spherical elec trode of any radius rs under conditions of constant flux Q, the concentration distribution is
C = C ---9-erfcf^^—1 1/2 47rDrs
|_(4D£) J
with a steady-state mass transfer coef ficient D/rs (compare with the mass transport coefficient to a large planar electrode, D/ôc; the minimum value of 5c a 0.001 cm for marked forced convection). Definitions of these and other symbols used in equations throughout this R E P O R T are provided in the glossary of symbols (see box). Unfortunately, the applicability of such types of microelectrodes has thus far been somewhat restricted to the electrodeposition of ensembles or single mercury droplets, the electrolysis of dispersions, or the dropping mercury microelectrode, to name a few examples. Disk and the recently introduced ring microelectrodes are more easily constructed, but the necessary mathematical analysis has thus far proved to be rather intractable. A related problem, the capacitance of a disk, was investigated experimentally by Cavendish in the mid-1700s. The mathematical difficulties of analyzing problems in the cylindrical coordinate system result from discontinuities at the edges of the electrodes where the diffusion-limited flux for a reversible system becomes infinite. The combined effects of the finite rates of the surface reactions and of the distribution of potential and concentration (i.e., the "tertiary current distribution"), however, limit the electron transfer rates at the edges for real systems. Microdisk and microring geometries, however, share the advantage of spherical microelectrodes; quasi-spherical diffusion fields are established in relatively short amounts of time. These spherical diffusion fields give high rates of mass transfer to the surfaces of
the microelectrodes so that the kinetics of fast electrode reactions and of fast reactions in solution can be studied un der steady-state conditions. Compli cated transient techniques at microelectrodes then may not be required, because it is now easy to build elec trodes with very small dimensions. It is therefore always useful to examine whether the steady-state behavior can be predicted directly. The steady-state behavior is described by the diffusion equation in the cylindrical coordinate system 2
dC dr2
|
1 dC r dr
the surface of a disk, the discontinuous integrals
sin(Xa)J0(Xr) — = —, r< a 2 sin_1| — J, r> a associated with
t
dC dz2
sm(\a)JQ(\t)dX =
= 0
- ί /(λ) exp(-Xz)J 0 (Xr)dX
where J0 is a Bessel function of the first kind of order zero. The /(λ) are sought so that the equation satisfies the ap propriate boundary conditions for any particular electrode geometry. For in stance, for a reversible reaction under constant concentration conditions at
Glossary of symbols used C° a ζ J0.J1 Q C6 b r D km 2 F, F
/ /Ό Z' Z" R CAv ω a
Bulk concentration, mol c m - 3 Radius of disk, inner radius ring, cm Coordinate normal to plane of disk, cm Bessel functions Flux, mol c m - 2 s~1 Surface concentration, mol cm - 3 Outer radius of ring, c m Radial coordinate, c m Diffusion coefficient, c m 2 s~ 1 Mass transport coefficient, c m s~ 1 Hypergeometric function Faraday constant, coulomb equivalent - 1 Current, amperes Exchange current density, amperes c m - 2 Real part, impedance Imaginary part, impedance Gas constant, J m o l - 1 K~ 1 Average concentration, mol cm"" 3 Angular frequency, Hz Transfer coefficient (in exp)
Ι Ο, r>a satisfy the boundary conditions pro vided /(λ) = (2/ir)AC sin(Xa). That is, we obtain the solution
C = C" - - ( Γ - Cs) Χ 1Γ
' exp(—λζ) sin(Xa)J0(Xr) -— λ Jo with flux F = W(C° - Cs)a and mass transfer coefficient (fem)c = AD/ττα. For the constant flux condition at a disk, the concentration distribution is
c = c~-^-x Jo
βχρ(-λ2) JoCXry^Xa) — λ
c = c°-
with mass transfer coefficient {km)q = 3πΌ/8α, where we take the average sur face concentration to be equal to zero, and where we have made use of another discontinuous integral. For the ring ge ometry under the same conditions, we find
% Γ Λ(αΓ)^(αα) erf(D1/2«i1/2) ^ fl Jo α and the chronopotentiometric re sponse for simple Butler-Volmer ki netics is
c=
l i DCw)\ 0 C- + % i"exp(-Xz)J(Xr) J(Xa) ^
0 xλ D Jo - ^ ["exp(-Xz)J0(Xr)J1(\6) ^ »transfer Jo coefficients, with av and massL erage concentration at the surface λ
equal to zero:
(kmh= 7^ = D(b2 - α2)
where £ 2 = Dt and β = a£ η Τ θ dc
Number of electrons reacting Absolute temperature, Κ Phase angle, rad Concentration boundary layer thickness, c m
Μ^)--(^))/ ρ*£ +βχρ(^)+ M^F)} Numerical evaluation of the inte grals is straightforward. Many of the equations may be expressed in terms of hypergeometric functions, which are convenient as these series generally converge rapidly and their propagation is simple and well-suited to representa tion by efficient algorithms. A com plete development of these equations, as well as expressions for several other experiments, are found in the litera ture cited in the Suggested Reading list. This approach can be extended to predict the non-steady-state behavior of disk electrodes for a variety of elec trochemical experiments. Although ex periments with very small electrodes will usually be carried out in the steady state (or under quasi-steady-state con ditions), the measurement of transient responses with readily available instru mentation becomes feasible for elec trodes having somewhat larger dimen sions. For instance, the concentration distribution at a disk for the simple case of chronopotentiometry is
2
After separating variables, we find a general solution of the form C=C°
i = F(km)QC" X
^ ^ . 2 a V i2(1 i , . i ; 2 ; 4 3ττ
3π
[2
2
VJ
These coefficients can then be used to determine the form of polarization curves. For instance, for a disk elec trode and a reaction obeying ButlerV n l m p r kirmti^c wo hnup
\ RT ;
«p(™)} = „ρ(^)_„ρ(α^)
The properties of these responses, such as the transition time, are close to those predicted by other workers even though other analyses have been based on the assumption of uniform surface concentration rather than constant flux conditions. The close agreement of results derived using the two approach es shows that the interpretation is not very sensitive to the nature of the as sumptions. The chronoamperometric response at a disk is found from determining what strength of sink, Q(s), in Laplace transform space gives a constant aver-
ANALYTICAL CHEMISTRY, VOL. 59, NO. 24, DECEMBER 15, 1987 · 1393 A
age surface concentration over the electrode. The result is
Q(S)=
( C - - CAu)a
Ï
X
pi/2 /
^/
ΓΪτ(8αέ!1\Ύ Jo L \ Dll2)\
άβ β(β2 + ΐ)2'
•tus β1/2« wlth ^=^ r Inverting to the time domain, the ex pression yields the known limiting cases: At short time intervals, we ob tain the Cottrell equation, and at long time intervals the known steady-state value 3nD(C - CAv)/8a. By a similar analysis, we find that the ac concentration at a disk is
c -
2Q
Αυ
1/2 1/2
x
£ ω Π τ /Wl2sin(a>t-e/2)d/3 ΙΐΎ l)\ β(1 + βΥ*
for a voltage perturbation of frequency ω. For Butler-Volmer kinetics, the im pedances are then given by:
Z' =
Figure 3. Current-time transient for the deposition of a single droplet of mercury from a solution 0.2 mM Hg2(N03)2 + 10 mM HN03; rj = 5 mV; 4-μιη radius carbon disk electrode. Top scale is the radius of the drop.
RT
+ 2RT TmFi0a2 wn2F2D1/2œ1/2a2C"
ing transitions between discrete cur rent levels. Transitions between levels are associated with the insertion-reori entation or removal-reorientation of Jo [ΎΟΙ β(1 + βψ4 single molecules of the peptide, which aggregate to form pores reaching a maximum size of 4-5 molecules. In sys 2 2 l/ 2 2 tems of this kind the generation of the wn F D W a C° current transducing element defines a "microelectrode" of molecular dimen Π τ / a a \ l 2 Bin(9/2)d/3 in a substrate having an area typi Jo Γ ΐ l)\ β(1 + βΥ* sions cally 1 mm 2 . The use of fire-polished capillaries to Application to other areas of isolate small patches of membranes has research in electrochemistry greatly extended the scope of such measurements. It should also be noted The investigations using microelecthat in systems of this kind the subse trodes also prompt a series of questions quent essentially deterministic trans regarding the connections with other membrane ion current amplifies the areas of research in electrochemistry. random aggregation-removal of the Here we consider both earlier investi pore-forming molecules so that the ki gations of the behavior of microelecnetics of these processes and the ener trodes and reinterpretation of the be getics of the states become measurable havior of known systems with a small at the molecular level (see also com number of examples. ments below on nucleation). The am Earlier investigations. The term plification results from the measure "earlier" here refers to investigations ment of a large flux of ions through the that had somewhat different objectives pore as the circumference of the pore from those of current research but that increases from 0 to 4-5 molecules, actually embodied many of the con whereas the latter parameters are in cepts now used. One of the best known vestigated by measuring the temporal examples is the use of microelectrodes development of the flux and its magni to stimulate and monitor physiological tude. processes. Examples of direct interest to the study of electrochemical kinetics A second large group of phenomena include ion transduction processes in that depend on the formation of microlipid bilayers. The application of an ap electrodes is that of the electrocrystalpropriate voltage difference to bilayers lization of new phases. For large elec containing the polypeptide alamethitrodes, these processes depend on the cin induces a current-time series shownucleation and subsequent growth of 1394 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 24, DECEMBER 15, 1987
centers of the new phase (i.e., we are dealing with the growth of ensembles of microelectrodes). In view of the very small dimensions of the centers (which
Ε (V vs. SCE)
Figure 4. Linear sweep anodic stripping voltammogram at a mercury drop elec trode (r = 7.0 μιτι) following a 10-min deposition in a quiescent solution con taining lead (8.7 Χ 10 - 8 M) and cadmi um ions (1.6 Χ 10 - 7 M) at - 8 0 0 mV vs. SCE. Scan rate was 50 mV s _1 . Reprinted from Wehmeyer, K. R.; Wightman, R. M. Anal. Chem., 1985, 57, 1989-93.
may well have radii 1-10 nm), diffusion is rapid so that the processes are controlled by the kinetics of the surface reactions and ohmic potential losses in solution are very low. Indeed, one can argue (see below) that the successful operation of many electrochemical devices depends on the formation of such ensembles of microelectrodes (e.g., the oxidation of P b S 0 4 to l 9-Pb0 2 in the lead acid battery). When electrocrystallization proceeds via the nucleation and growth of two-dimensional centers of monomolecular height (as is observed in the variety of anodic films or in the deposition of silver on perfect single-crystal [100] substrates), the processes can be modeled as the growth of circular or polygonized microelectrodes. The deposits are usually highly oriented so that we observe electrode reactions in defined crystallographic directions (i.e., lattice formation at the edges of layer planes of the lattice). In these cases, one characteristic length scale of the microelectrodes is of atomic dimensions and consequently, the observable rates of reaction are very high. The steps propagate over the surface into regions of the solution where the reagents have not been depleted so that, in contrast to stationary "line" electrodes, very high rates of steady-state mass transfer can be achieved (several hundred centimeters per second). The modeling of mass transfer to arrays of such edges (such as those generated by emergent screw dislocations on surfaces of growing crystals) has in fact been known for quite some time. Catalytic reactions at the edges of island films and at "holes" have also been studied (e.g., hydrogen evolution at ruthenium layers and the oxidation of CO adsorbed on Pt). Mass transport rates of oxygen to the edges of microislands of adsorbed CO will be extremely fast, because the islands are small and the reaction rate is high. Reinterpretation of the behavior of known systems. The application of microelectrodes also provides new opportunities for simplifying and extending research into well-known systems. For example, it becomes possible to investigate the formation of single or, at most, a few growth centers. These processes are illustrated in Figure 3 with the growth of a single droplet of mercury (cf. Figure Id and analytical applications, Figure 4) and of a single center of a-Pb02 (Figures 5 and 6) on carbon microelectrodes. Figure 3 shows that the reaction is kinetically controlled in the initial stages and that it is now feasible to make measurements on such electrodes having characteristic dimensions of ~10 nm. This is shown more clearly by the second example, which is a much slower reaction, where the time of nucleation is
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ph Figure 5. Deposition of two growth centers of α-PbO onto an 8-μιη diameter carbon microelectrode. The solution composition: 0.1 M Pb(Ac)2 + 1 M HAc; η = 400 mV; deposition time = 120 s.
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marked by the onset of the kinetically controlled growth even at very high overpotentials. We see that in this ex ample, as in the voltage-gated trans membrane ion currents, the subse quent essentially deterministic pro cesses allow the observation of the initial stochastic events so that it be comes possible to investigate kinetics of the nucleative trigger events. Note that if the electrodes are suffi ciently small, it becomes possible to in vestigate the probability distribution of the reaction rates for ensembles of experiments and hence the higher mo
ments of the kinetic parameters of the kinetic processes. The interpretation of the higher moments of the reaction rates is highly diagnostic of the mecha nisms of the reactions; the measure ment and interpretation of electro chemical "noise" therefore promises to be a further important area for the ap plication of microelectrodes to analyti cal and physical problems. The application of microelectrodes will undoubtedly lead to many novel ways of investigating established sys tems. For example, in addition to the investigation of low-temperature fro-
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Flgure 6. Current-time transient for the deposition of a-Pb02 onto an 8-μιη microelectrode.
1396 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 24, DECEMBER 15, 1987
zen solvents, microelectrodes are already being applied to the investigation of polymer-modified electrodes. The electrolysis of dispersion of particles affords new opportunities for probing and monitoring heterogeneous catalysis and for devising new conditions for electrosyntheses. It is possible to make electrodes having at least one dimension comparable to or smaller than the Debye screening length (e.g., by using line or ring electrodes). Measurements with such electrodes should therefore provide a new tool for probing double-layer structure. Application to other areas of analytical and physical research The investigation of novel systems prompts a series of questions about the connection between such electrochemical measurements and other established fields of analytical and physical research. Some of these connections are evident from the advantage of microelectrode systems that have been described. For example, Figure 4 illustrates the very high sensitivity that can be achieved using simple techniques. Very high S/N ratios are observed in stripping voltammetry experiments, even at the 100 nanomolar level. Moreover, these measurements can be made on very small samples.
Table 1. Connections between the investigation of electrochemical systems using microelectrodes and other fields of research Phases measured with mlcroelectrodes
Relevant areas of research
Liquid (types 1 and 2)
High field charge injection Scanning tunneling microscopy Heterogeneous catalysis
Solid (type 3)
Charge transfer in solids Reactions in solids Charge injection into insulators
Gas (type 4)
Thermionic emission Field emission microscopy Scanning tunneling microscopy High field ionization (generation of parent ions) High-vacuum experiments Heterogeneous catalysis
Other applications, or at least connections to other applications such as those listed in Table I, are perhaps not so self-evident. The subject divisions in Table I are naturally somewhat arbitrary. For example, consideration of the conditions for field ion microscopy or high-field ionization are as relevant
to studies in the liquid phase as to those in the gas phase. We note that research in the "other areas" listed in Table I usually has objectives (such as the imaging of surfaces, the generation of parent ions for analytical mass spectrometry, the charging of fuels or polymers) that do not include the study of
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1398 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 24, DECEMBER 15, 1987
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the interfacial charge transfer steps. However, the total description of the processes must certainly include that of the surface reactions. It should prove possible to design many interesting new experiments, for example, the ex amination of the structure of polarized surfaces using high-vacuum techniques such as RHEED (high vacuum rather than ultra-high vacuum). Conclusion
In this R E P O R T we have pointed out some of the approaches that may be used to predict the electrochemical re sponse to finite electrode geometries, and we have described some new direc tions that electrochemistry is taking. The future value of microelectrodes will lie in the continued application of the devices to new systems and the re investigation of systems with new goals in mind. Applications in new environ ments will lead to sensors and detectors for Dractical use. Suggested Reading General References and Theory
Fleischmann, M.; Pons, S.; Rolison, D.; Schmidt, P. P. Ultramicroelectrodes; Datatech Science: Morganton, N.C., July 1987. (Text treating fabrication of microelectrodes, steady- and non-steady-state theory at microelectrodes, and a general review of applications) Bond, A. M.; Fleischmann, M; Khoo, S. B.; Pons, S.; Robinson, J. Ind. J. Tech. 1986, 24, 492. (Review on applications and the ory) Wightman, R. M. Anal. Chem. 1981, 53, 1125 A. (Earlier review on microelec trodes) Fleischmann, M.; Pons, S. J. Electroanal. Chem. 1987,222,107. (Application of dis continuous integrals to disks and rings) Aoki, K.; Akimoto, K.; Tokuda, K.; Matsuda, H.; Osteryoung, J. J. Electroanal. Chem. 1985,182,281. (Approximate solu tion to the chronopotentiometric re sponse at the disk) Heinze, J. J. Electroanal. Chem. 1981,124, 73. (Simulations of the disk response) Oldham, K. B. J. Electroanal. Chem. 1981, 122,1. (Analysis of the disk response) Szabo, Α.; Cope, D.; Tallman, D. E.; Kovach, P. M.; Wightman, R. M. J. Electroanal. Chem. 1987, 217, 417. (Treatment of hemicylinder and line electrodes) Applications
Kim, Y. T.; Scarnulus, D. M.; Ewing, A. G. Anal. Chem. 1986,58,1782. (Carbon ring microelectrodes) Miller, B.; Rosamilia, J. M. J. Electrochem. Soc. 1985,132, 2621. (Semiconductor mi croelectrodes) Tallman, D. E.; Weisshaar, D. E. J. Liq. Chromatogr. 1983, 6, 2157. (Liquid chro matography detectors) Whelan, D.; O'Dea, J. J.; Osteryoung, J.; Aoki, K. J. Electroanal. Chem. 1986,202, 23. (Square-wave voltammetry at micro electrodes) Howell, J. O.; Wightman, R. M. J. Phys. Chem. 1984, 88, 3915. (Electrochemistry in highly resistive nonpolar solvents) Bond, A. M.; Fleischmann, M.; Robinson, J. J. Electroanal. Chem. 1984, 768, 299. (Electrochemistry in polar solvents with out electrolytes) Cassidy, J.; Khoo, S. B.; Pons, S.; Fleisch
mann, M. J. Phys. Chem. 1985, 89, 3933. (Oxidations at very high positive poten tials) Dibble, T.; Bandyopadhyay, S.; Ghoroghchian, J.; Smith, J.; Sarfarazi, F.; Fleisch mann, M; Pons, S. J. Phys. Chem. 1986, 90, 5275. (Electrochemistry of the rare gases) Fleischmann, M.; Ghoroghchian, J.; Pons, S. J. Phys. Chem. 1985, 89, 5530. (Electro chemistry of dispersions of microelec trodes) Fleischmann, M.; Ghoroghchian, J.; Roli son, D.; Pons, S. J. Phys. Chem. 1986,90, 6392. (Electrochemistry of dispersions of microelectrodes) Feldman, B. J.; Murray, R. Anal. Chem. 1986,58,2844. (Solid-state electrochemis try at microelectrodes) Bond, A. M.; Fleischmann, M.; Robinson, J. J. Electroanal. Chem. 1984, 180, 257. (Electrochemistry in low-temperature glasses and eutectics) Ghoroghchian, J.; Sarfarazi, F.; Dibble, T.; Cassidy, J.; Smith, J.; Russell, Α.; Fleisch mann, M.; Pons, S. Anal. Chem. 1986,58, 2278. (Gas-phase electrochemistry) Bond, A. M.; Fleischmann, M.; Robinson, J. J. Electroanal. Chem. 1984, 172, 11. (Treatment of ohmic losses at microelec trodes) Fleischmann, M.; Lasserre, F.; Robinson, J.; Swan, D. J. Electroanal. Chem. 1984,177, 97. (EC and CE reactions at microelec trodes) Fleischmann, M.; Lasserre, F.; Robinson, J. J. Electroanal. Chem. 1984, 177, 115. (ECE and DISP reactions at microelec trodes) Russell, Α.; Repka, K.; Dibble, T.; Ghorogh chian, J.; Smith, J.; Fleischmann, M.; Pitt, C. H.; Pons, S. Anal. Chem. 1986, 58, 2961. (Determination of heterogeneous electron transfer rates)
Stanley Pons (left) is professor of chemistry at the University of Utah. His research interests include vibra tional spectroelectrochemistry, appli cations of microelectrodes, and mech anistic studies of electrochemical re actions. He has published more than 100 research articles in these areas. Martin Fleischmann (right) is profes sor of chemistry at the University of Southampton. He is a Fellow of the Royal Society and was recently award ed the Palladium Medal from the Electrochemical Society. He is the au thor or coauthor of numerous publica tions in electrochemistry and electroanalytical chemistry. His interests in clude electrochemistry at the molecular level, in situ X-ray diffrac tion of electrode surfaces, and other in situ techniques applied to electro chemistry.
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