peak shapes in semidifferential electroanalysis

stirred deposition interval. A linear dependence of peak current upon scan rate was obtained (linear regression cor- relation coefficient = 0.9997) so long as the quantity of coulombs involved in the stripping process remained constant.

The dependence of first and second harmonic responses in ac voltammetry on experimental parameters was recently outlined by Smith et al. (26). The effect of dc scan rate was not described explicitly in this study, although the basic equations involved in ac voltammetry were presented which show that the alternating current response is proportional to surface concentrations of oxidized and reduced forms. Since deposited mercurous mercaptide is insoluble in the solution and electrode phases, its activity should be near unity throughout the stripping scan (27) and the resulting PSCS current response proportional to mercaptan concentration a t the electrode surface. Thus, the square root relationship of PSCS peak currents and scan rate results primarily from the dependence of generated mercaptan surface concentrations upon dc scan rate.

ACKNOWLEDGMENT The authors are grateful to Donald E. Smith for aid in

understanding the scan rate dependence of PSCS peak currents.

LITERATURE CITED (1) E. Barendrecht in “Electroanalytical Chemistry-A Series of Advances”,

Voi. 2, A J. Bard, Ed., Marcel Dekker, New York, N.Y., 1967, pp 53-109, (2) W. Kemula and 2. Kubik in “Advances In Analytical Chemistry and

Instrumentation”, Vol. 2, C N. Reiliey, Ed., Interscience, New York, N.Y., 1963, Chap 3.

(3) I. Shain in “Treatise on Analytical Chemistry”, Part I, Vol. 4, I. M. Koltoff and P. J. Eiving, Ed., Interscience, New York, N.Y., 1963, Chap. 50.

(4) G. Colovos, G. S. Wilson, and J. L. Moyers, Anal. Chem., 46, 1051 (1974). (5) Kh. Z. Brainina, Talanfa, 18, 513 (1971). (6) H. Berge and P, Jeroschewskl, Fresenius’ 2. Anal. Chem., 212, 278

(1965). (7) M. J. D. Brand and B. Fleet, Analyst(London), 93, 498 (1968). (8) D. A. Csejka, S. T. Nakos, and E. W. DuBord, Anal. Chem., 47, 322

(1975). (9) E. D. Moorhead and P. H. Davis, Anal. Chem., 45, 2178 (1973).

(IO) E. D. Moorhead and P. H. Davis, Anal. Chem., 47, 622 (1975). (11) E. D. Moorhead and G. A. Forsberg, Anal. Chem., 46, 751 (1976). (12) M. L. Mittal and A. V. Pandey, J. Electroanal. Chem., 36, 249 (1972). (13) R. S. Saxena and U. S. Chaturvedi, J. Electroanal. Chem.. 36, 515 (1972). (14) W. Strlcks, J. K. Frischman, and R. G. Mueller, J. Nectrochem. Soc.,

log, 518 (1962). (15) S. Kukuchi, Bull. Chem. SOC. Jpn., 27, 65 (1954). (16) T. M. Florence and Y. J. Farrar. J. Nectroanal. Chem., 41, 127 (1973). (17) A. M. Bond, Anal. Chem., 44, 315 (1972). (18) A. M. Bond and J. H. Canterford, Anal. Chem.. 43, 228 (1971). (19) A. M. Bond, Talanta, 20, 1139 (1973). (20) W: L. Underkofler and I. Shain, Anal. Chem., 37, 216 (1965). (21) J. R. Delmastro and D. E. Smith, Anal. Chem., 38, 169 (1966). (22) J. J. Lingane, J . Electroanal. Chem., 1, 379 (1960). (23) Princeton Applied Research Corporation, Prlnceton, N.J., Application Note

108. (24) D. E. Smith in “Electroanalytical Chemistry-A Series of Advances”, A.

J. Bard, Ed., Marcel Dekker, New York, N.Y., 1966, Chap. 1. (25) M. Brezlna and P. Zuman, “Polarography in Medicine, Biochemistry, and

Pharmacy”, Interscience, New York, N.Y., 1956, pp 470-478. (26) A. M. Bond, R. J. O’Halloran, I. Ruzic, and D. E. Smith, Anal. Chem.,

48, 872 (1976). (27) T. Berzins and P. Delahay, J . Am. Chem. Soc., 75, 555 (1953).

RECEIVED for review February 22,1977. Accepted April 27, 1977. This material was presented in part at the 3rd Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies in Philadelphia, Pa., November 1976.

Peak Shapes in Semidifferential Electroanalysis

Penny Dalrymple-Alford

Trent University, Peterborough, Canada

Masashi Goto

Nagoya University, Japan

Keith 6. Oldham”’

Bristol University, United Kingdom

A derlvative neopolarogram Is the peaked curve that is generated by semidlfferentlatlon of the current that flows In response to an imposed ramp slgnal on a stationary electrode. The predicted dependences of peak height, peak potentlal, and peak wldth on concentration, electron number, scan rate, etc., are confirmed experimentally uslng one established and two new clrcuits to monitor the electroreductlon of several metal Ions in aqueous solutlon. Features of the technique that make it attractlve for qualltatlve and quantltatlve chemlcal analysis are cited, and comparlson Is made with pulse polarography.

Semidifferential electroanalysis was first described by Goto and Ishii (I). More recently, the present authors (2) have

‘Permanent address, T r e n t Universi ty, Peterborough, Canada.

discussed some theoretical aspects of this voltammetric technique. The purpose of the current article is to compare the theoretical predictions with experimental data, to demonstrate that semidifferentiation may be effected digitally or by simpler circuitry than that used hitherto, and to discuss the analytical potentialities of the method.

In semidifferential electroanalysis, a cathodic-going ramp signal is applied to a working electrode immersed in a solution containing, in addition to excess supporting electrolyte, one or more species that are electroreducible. The semiderivative e of the cathodic current that flows in consequence of the electroreduction is displayed as a function of the applied potential E. Figures 1 and 2 show examples of the resulting curves, which are termed “derivative neopolarograms” (2). A derivative neopolarogram consists of one or more peaks, each of which corresponds to a single reduction process. In Figure 1, for example, the two peaks correspond to the reductions of the In3+ and Zn2+ ions. Each peak is independent of the others; thus when In3+ was omitted from the solution used

1390 ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977

-600 - S O 0 -1000 E ( m V v s SCE)

Flgure 1. A derivative neopolarogram of 100 YM In(II1) and 100 yM Zn2+ in 100 mM KCI. Scan rate: 100 mV s- : electrode area: ap- proximately 4.5 mm'; instrumentation: Circuit c

30

2 0

10

-400 -600 -SO0 -1000

Flgure 2. A derivative neopolarogram of 1 .O mM each of TI', Cd", and Ni'' in 100 mM K N 0 3 . Scan rate and electrode area: as Figure 1; instrumentation: Circuit B

to generate Figure 1, the Zn2+ peak remained unchanged. A derivative neopolarographic peak may be characterized

by three features: e,, the peak height (the maximum value attained by the semiderivative); E,, the peak potential (the potential corresponding to the maximum); and W,, the peak width (the potential range spanned by the peak at a height equal to one-half the maximum height). The values predicted (2) for these features are listed in Table I for both reversible and irreversible electroreductions. The symbols used in this tabulation have the following significances: n is the number of faradays needed to reduce 1 mol of the reducible species; F and R are Faraday's and the gas constants (96 487 C mol-' and 8.3143 J K-' mol-'); T is the temperature (K); c and D are the concentration of the reducible species and its diffusion coefficient (mol m-3 and m2 8); a is the transfer coefficient of the electron exchange process; A is the area of the electrode (m2) and u is the rate (V s-') at which it is made more negative; E!,z is the halfwave potential (V) in classical polarography with a dropping mercury electrode, 7 being the corresponding droptime (s).

Notice in Table I that the peak height, for both reversible and irreversible processes, is predicted to be proportional to the concentration of the reducible species, to the electrode area, and to the scan rate u. The peak potential for reversible process is a constant equal to the polarographic halfwave

Table I. Features of Derivative Neopolarographic Peaks Reversible Irreversible

a n2F'A ucD ' I 2 n F2A U C D " ~ __.- Peak height, e ,

4RT 3.367 RT

Peak potential, E , E,,, RT

2anF El,, f -

R T R T nF anF

Peak width, W, 3.53 - 2.94 -

r o : l 0

0 -03 - 0 6 -09 - 1 2 E( v vs. SCE)

Flgure 3. Comparison of resolutions of a derivative neopolarogram, a voltammogram, and a neopolarogram of the same four-component solution: 50 yM each of (a) Cu2+, (b) Pb2+, (c) Cd2+, and (d) Zn'+ in 100 mM KNOB. Scan rate: 100 mV s-'; electrode area: 4.69 mm2; instrumentation: Circuit A

potential, but for irreversible reductions E, should typically be about 45 mV negative of (based on an = 1 and u = 100 mV s-l) and will shift cathodically as the scan rate is increased (by 30 mV for a tenfold u increase). The peak shape is very dependent on n, the number of transferred electrons: as n increases, the peak is predicted to become narrower and much higher.

The formulas given in Table I are predicated on a planar electrode, whereas in the Experimental section of this article the electrodes used are hanging mercury spheres. However, it has been demonstrated (2) that the mild sphericity en- countered in our experiments is adequately corrected for by subtracting the quantity iD'l2/r from measured values of e. Here i denotes the cathodic current and r is the radius of the mercury drop. We shall use a tilde to indicate quantities corrected in this way; thus I = e - (iD1I2/r) and E,, represents the peak of an I vs. E curve.

Semidifferential electroanalysis is closely related to the techniques of linear scan voltammetry (3) and semiintegral electroanalysis (4) ; in fact, it is simply the derivative of the latter. That linear scan voltammetry is a method intermediate between semiintegral electroanalysis and semidifferential electroanalysis is brought out in Figure 3. Whereas linear scan voltammetry is the easiest of the three techniques to implement, it is the most difficult to interpret. Implemen- tation with linear scan voltammetry is easy because the displayed quantity is simply the current i. To obtain e , the quantity displayed in semidifferential electroanalysis, however, requires the processing of i data. We now take up the topic of how i is semidifferentiated to obtain e.

IMPLEMENTATION As with semiintegration, two techniques are available for

semidifferentiation: digital and analog. Digital methods will be preferred whenever computer-augmented experimentation

ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977 1391

Scheme I i rdifferentiate + e

Lsemiintegrate + m

Scheme I1 -semidifferentiate + e I

i

Scheme I11 pemidifferentiate + e -subtract -. T i attenuate-

Scheme IV ,-differentiate +

i 1 I

semiintegrate + m - subtract + 2 t integrate + q - attenuate

is employed, or when data of the highest accuracy are sought. Under other circumstances, the tedium of numerical semidifferentiation may be avoided by analog instrumentation. Sphericity correction is a simple matter with either technique.

Digital Techniques Several algorithms for numerical semidifferentiation have been described (5). The simplest, the so-called G1 algorithm, uses N equally spaced current data to compute e by the concatenation scheme

+ i,]. .I(;)+ i N - ’ [ ( 3 > f iN]

which is very easily implemented by a multiplication-addition-multiplication- ... multiplication-addition procedure. In this algorithm, i1, i ~ , is, ... i ~ - ~ , and i~ denote the instantaneous currents a t times t / N , 2t /N, 3t/N, ... (N - l ) t / N , and t. As with all algorithms, there is a discretization error implicit in this G1 formula; its magnitude diminishes as N increases.

Analog Techniques. A number of analog schemes are possible whereby the cell current may be electronically processed to give a signal proportional to e. The instrument previously described ( I ) is based on Scheme I. whereas a more direct scheme, Scheme 11, is also possible. When correction for the sphericity is introduced, the direct scheme, Scheme 111, becomes significantly simpler than Scheme IV ( I ) . In the Experimental section of this article, we describe results obtained with instrumentation based on Schemes I1 and IV. The latter, which will be referred to as Circuit A, differs from that previously described ( I ) only in having a gain-adjustment potentiometer inserted between the subtractor and differ- entiator stages. The instrumentation based on the direct Scheme I1 will be described in some detail below. In use, it has been incorporated into the output stage of a Princeton Applied Research Corporation Model 170 Electrochemical System.

The output of the PAR 170 is a dc voltage in the range -10 V to +10 V, proportional to the electrochemical current. This output is normally fed (via an optional 1 O : l attenuator) di- rectly to the Y-drive of the instrument’s X-Y recorder. Our modification is to insert a battery-powered operational amplifier circuit into the output lead. A rotary switch enables a variety of circuit elements to be inserted into the input of the operational amplifier, and into its feedback loop. However, the only circuits relevant to the present experimentation are those shown in Figure 4, both of which semidifferentiate.

B - -

PAR 170 PAR 170 output y chart drive

- -

PAR 170

Y chart drive PAR 170

4F- ou tpu t -

Flgure 4. Circuits B and C, the two direct semldifferentiators. In both circuits LAD represents the ladder network shown as Figure 10 in Ref. 6 except that an 8300-kR resistor replaces the one mislabeled 830 k n in the publlcation

By arguments that closely parallel those governing the behavior of semiintegrating circuits (6) it can be shown that the output of a circuit resembling Figure 4B is

where Vi, is the input voltage, Rf is the feedback resistance and the ratio is a characteristic impedance term for the ladder network. In our circuit, Rf equals 2.00 megohms, RI/CI equals 1.00 megohm per microfarad, and therefore

A l l 2 U vout = -(2.00 SI/*) - dt1/2 vh

When incorporated into the PAR 170 system as described above, the effect of the Figure 4B modification is to multiply the PAR 170 sensitivity setting by the factor 0.5 s-Ii2, and to change the sign; thus with the current range set to “100 microampere full scale”, the actual full scale signal is 50 PA

Similarly the circuit in Figure 4C processes a voltage signal s-1i2*

according to the

R1 d‘” d,’ l 2 4 c1 d t ’ ’ 2 dt ’” Kn = - ( L O O P)- v, Vout = -ci - -

rule. Apart from the sign inversion, the effect of this modification is simply to change the unita of the sensitivity setting. Thus if the unmodified instrument has a full scale deflection when the electrochemical current is 20 FA, full scale deflection is achieved after modification when the semiderivative of the electrochemical current is 20 MA s-’/*.

EXPERIMENTAL Hydrates of the salts Zn(NO&, Cd(NOJ2, TlN03, InCl3,

Ni(N0J2, ZnS04, Pb(N0J2, and CuS04 were used as solutes in either 100 mM KN03 or 100 mM KCl. Solutions were prepared by direct weighing of the appropriate quantities of “laboratory grade”, “analytical grade”, or “special grade” reagents, without further purification. Prior to the electrochemical experiments, solutions were deoxygenated by passage of Ar or N2 gas.

A hanging mercury drop (Beckman Model 39016) working electrode and a saturated calomel reference electrode were used. Drop areas and radii were calculated from the metered volume of extruded mercury by assuming the electrode to be a perfect sphere. Measurements were made at room temperature, 293-296 K.

The instrumentation was either Circuit A: that described in the prior publication (I); or the PAR 170 instrument augmented as described above: Circuit B or Circuit C. Sphericity correction was incorporated into the results obtained using Circuit A, but


Table 11. Peak Potentials for Cd" and Ni" Derivative Neopolarograms

Ep for CdZt/ E, for NiZ+/ C/PM mV vs. SCE mV vs. SCE

20 -571 -1015 40 -570 -1022 60 -571 -1028 80 -575 -1025

100 -573 -1026 Theoretical -578 -1034

(see text) Supporting electrolyte: 100 mM KNO,; scan rate: 100

mV s-l; electrode area: 4.69 mmz; instrumentation: Circuit A.

Flgure 5. Relationship between peak heights of derivative neopoia- rograms and electrode area. 0: 100 pM Cd2+ In 100 TM KNOB; 0: 100 KM Ni2+ in 100 mM KNOB; scan rate: 100 mV s-

' - 1

/

Flgure 6. Relationship between peak heights of derivative neopolarograms and scan rate. Solutions: as Figure 5; electrode area: 4.69 mm2

5 , I

C (pM)

Figure 7. Relationship between peak heights of derivative neopolarograms and concentration of electroactive solutes GI2+ (0) and Ni2+ (0). Scan rate: 100 mV s-'; electrode area: 4.69 mm2; supporting electrolyte 100 mM KNOB

not into those using Circuits B or C, which were of a more qualitative nature.

RESULTS Figures 1, 2, and 3 show derivative neopolarograms for an

assortment of reversibly and irreversibly reduced cations, using Circuits C, B, and A, respectively. Figure 3 also shows the corresponding linear scan voltammogram and neopolarogram.

Table I predicts a linear dependence of peak height on each of three experimental variables: the electrode area A , the potential scan rate v , and the concentration c of the electroactive species. These proportionalities are tested in Figures 5, 6, and 7 for Cd2+ (reversible) and Ni2+ (irreversible) reductions. In all cases linearity is satisfactory and the lines pass through the origins.

The slope dB,/dc for Cd2+ in Figure 7 has an experimental value of 43 p A s-'I2 m3 mol-', com ared with a theoretical

the basis of a diffusion coefficient (7) of 6.9 x lo-'' m2 s-'. Similarly for the Ni2+ line, the experimental slope dk,/dc = 21 pA s-'I2 m3 mol-' compares well with the theoretical value otn2AF%D112/3.367RT = 20 p A s?I2 m3 mol-', based on D = 6.9 X 10-l' m2 s-' (8) and LY = 0.36 [from a plot (9) of In (md - m/i ) vs. E ] . The slopes of the lines in Figures 5 and 6 are

value, n2AF%D112/4RT of 46 pA s-' P m3 mol-', calculated on

Table 111. Scan Rate Dependence of the Peak Potential of CdZt and Nil' Derivative Neopolarograms

&/mV vs. SCE u/mV s-' CdZt (exptl) Ni" (exptl) NiZt (theor)

20 -574 -1007 -1001 40 -573 -1015 -1012 60 -1020 -1019 80 -575 -1022 -1024 100 -573 -1026 -1027 120 -576 -1028 -1030 140 -1030 -1033 160 -576 -1035 -1035 180 -1035 -1038 200 -579 -1041 -1039

Supporting electrolyte: 100 mM KNO,; electroactive concentration: 100 WM; electrode area: 4.69 mm2; instrumentation: Circuit A.

Table IV. Peak Width Values for Cd2+ and Ni2' Derivative Neopolarograms

i7 for i7 for c/bM v/mV SK' A/mm' CdP+/rnV Niz'/mV

20 100 4.69 45 109 4 0 100 4.69 46 105 60 100 4.69 47 98 80 100 4.69 46 105 100 20 4.69 46 100 4 0 4.69 47 98 100 120 4.69 47 103 100 160 4.69 50 101 100 200 4.69 105 100 100 2.48 46 104 100 100 4.02 46 102 100 100 4.69 46 100 100 100 5.31 46 102 100 100 6.47 46 104 100 100 7.53 48 103

Theoretical: 45 103 Conditions: as Table 11.

likewise within a few percent of the predicted values. The derivative neopolarographic peak potentials E, for the

reduction of Cd2+ and Ni2+ ions were found to be independent of concentration, as shown in Table 11, and to average respectively -572 and -1023 mV vs. SCE (the latter value refers to v = 100 mV s-'). The experimental Cd2+ peak potential of -572 mV vs. SCE is to be compared with the 1iterFture polarographic E1/2 value (7) of -578 mV vs. SCE. The E, for Ni2+ of -1023 mV vs. SCE may likewise be compared with the -1034 mV vs. SCE value calculated from the halfwave potential (-980 mV vs. SCE a t T = 4.48 s) in classical polarography (8) by application of the relation in Table I.

For Ni2+, the peak potential should vary with scan rate in accordance with the relationship contained in Table I, while

ANALYTICAL CHEMISTRY, VOL. 49, NO. 9, AUGUST 1977 1393

E , should be u-independent for Cd2+ reduction. Table I11 reports the experimental data and, in the nickel case, lists the theoretical E , on the assumption that a equals 0.39. Agreement is within a few millivolts in all cases.

Table IV assesses how well the observed peak widths in semidifferential electroanalysis agree with theoretical predictions. The data refer to the reductions of Cd2+ (reversible) and Ni2+ (irreversible) in 100 mM KNOB supporting electrolyte. The theoretical predictions are again based on Table I.

In addition to the experimental correlations with theory that have just been described, numerous comparisons were also carried out of derivative neopolarographic features with neopolarographic features (9). As might be expected, the agreement is even closer than those we have reported above.

DISCUSSION All theoretical predictions concerning semidifferential

electroanalysis have been adequately confirmed. It is evident from Figures 1 through 3 that semidifferential

electroanalysis provides an attractive and efficient method for the identification and assay of electroactive solute species. Features of the method that should be noted include: ease of correction for electrode sphericity; the independence of the measured response on any prior electrode process that may have occurred; the good resolution (see Figure 2) between adjacent peaks; the marked dependence of peak shape on electron number; the fact that the “gain” of the method is adjustable by changing the scan rate; the distinguishability of irreversible from reversible peaks because of the independence of peak potential on scan rate for reversible electroreductions; and the possibility of exploiting v-dependence in irreversible cases to separate two peaks that would otherwise overlap. Though this entire article is couched in terms of cathodic processes, it is evident that the conclusions are easily widened to embrace electrooxidations.

The readout in semidifferential electroanalysis resembles a differential pulse polarogram. In fact, the two techniques have much in common. Thus, for reversible processes, the peak shape is exactly the same in the two techniques (IO), so that the peak potentials and peak widths coincide (for small enough pulse amplitudes a). Moreover, very similar factors enter into the determination of the peak height, as will be apparent on comparison of the first entry in Table I with the corresponding expression,

for the peak height in differential pulse polarography. One feature in which semidifferential electroanalysis excels is the speed with which a determination can be made: one second may suffice for the complete run.

The method suffers from the disadvantages inherent in the use of hanging mercury drop electrodes and, in this connection, one thinks particularly of surface contamination of the mercury by adsorbable impurities. Though we have not attempted to implement it, one solution to this difficulty would be to adapt semidifferential electroanalysis to the later stages in the life of a dropping mercury electrode. In fact, as long ago as 1959, Barker (11) made essentially the same

suggestion as a means of improving the readout in linear scan voltammetry a t a dropping electrode.

Experiments with Cd2+ at dilutions much greater than those reported above suggest a detection limit in semidifferential electroanalysis of about 100 nM: this is comparable to the limit cited by Bond (12) for differential pulse polarography, though detection limits as low as 10 nM have been claimed (13) for this pulse technique. A less empirical method of assessing the lowest detectable concentration is to compare the faradaic signal ep with the background signal arising from interfering effects. If we take the latter to be predominantly the nonfaradaic contribution from charging the capacitance Cd of the double layer, then the magnitude of the interference can be found by semidifferentiating the expression

‘nf = -ACd(dE/dt) = ACdv for the nonfaradaic current, to give

as the capacitative contribution to the semiderivative a t the peak potential. The detection limit may now be compared with the concentration at which the faradaic contribution to the signal equals 10% of the total signal. Using Table I we find this concentration to be

711/2 2 2

for a reversible peak. Notice the squareroot dependence on the scan rate, and the inverse squareroot dependence on the length Eo-E, of the potential range available prior to the peak. Taking n = 2, Cd = 0.2 F m-’, D = 1 X lo-’ m2 s-l, Eo-E, = 0.5 V, and v = 0.1 V s-’, this formula gives 50 nM, close to the detection limit found empirically. Decreasing the scan rate should permit even lower concentrations to be detected.

ACKNOWLEDGMENT We are grateful to Daido Ishii for his helpful advice, and

0.44 RTCdUI” TI F D1/*(E, -E,)”*

to Ian Williams for computational assistance.

LITERATURE CITED (1) M. Goto and D. Ishii, J. Nectroanal. Chem., 61, 361 (1975).

I P. Dalrymple-Alford, M. Goto, and K. B. Oldham, J. Electroanal. Chem., in press. R. S. Nicholson and I. Shain, Anal. Chem., 36, 706 (1964). M. Grenness and K. B. Oldham, Anal. Chem., 44, 1120 (1972). K. B. Oldham and J. Spanier, “The Fractional Calculus”, Academic Press, New York, 1974. K. B. Oldham, Anal. Chem., 45, 39 (1973). J. Heyrovsky and J. Kuta, “Principles of Polarography”, Academic Press, New York, 1965. P. Kivalo, K. B. Oldham, and H. A. Laitinen, J. Am. Chem. Soc., 75, 4148 (1953). M. Goto and K. B. Oldham, Anal. Chem., 45, 2043 (1973). E. P. Parry and R. A. Osteryoung, Anal. Chem., 37, 1634 (1965). G. C. Barker, “Proceedings of the Second International Congress on Polarography, Cambridge 1959”, Pergamon Press, London, 1960, p 140. A. M. Bond, Anal. Chlm. Acta, 74, 163 (1975). G. C. Barker and A. W. Gardner, Fresenius’ 2. Anal. Chem., 79, 173 (1960).

RECEIVED for review July 9, 1976. Resubmitted January 26, 1977. Accepted May 2,1977. The authors thank the National Research Council of Canada for continuing support, and the United Kingdom Science Research Council for the award of a Senior Visiting Fellowship.


peak shapes in semidifferential electroanalysis

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