Tuned Alternating Current Polarography SIR: The sensitivity of a.c. polarography in its simplest form (2) is limited by the high background current due to charging of the electrical double-layer capacity a t all but very low frequencies (.LORDI College of Pharmacy Rutgers University Kewark, X. J. RECEIVEDfor review August 28, 1962. -4ccepted October 8, 1962.
Integration of Oscillopolarograms in the Study of Electrode Reactions SIR: Recently there has been a n increased interest in the use of potential sweep (oscillographic polarographic) methods in the study of electrode reaction mechanisms (4, 9,15). S u m e r ous analytical applications of the technique have also been reported u hich exploit the linrar relationship between the peak current in a typical current-potential curve and the concrntration of the reacting substance (3,iO.I S ) . We have recently observed t h a t the measurement of the current-time integral, rather than the pcak currrnt, during the course of a potrntiostatically applied lincar potential sm eep offers considerable promise as a procedure for the quantitative deterniination of reactants adsorbed on elcctrode surfaces and as a method for wparating contributions from oxidation or reduction of the electrode which often accompany electrode reactions (6). [Breiter ( 1 ) has used current-time iiitegrals to study reactant adsorption but his approach differs considerably from t!iat deqcribed below.] SnoIT-den and Page (15) described a procedure for integration of oscillopolarographic waves in 1950, but they did not pursue the technique. For a reversible electrode reaction, the current-potential relation observed
during a potential sweep experiment may be written as
where n, F , R, T, A , D,and C have their usual significance, v is the time rate of change of potential of the electrodeconstant during any single experimentand P is a function of vt ( 9 ) . The coulombs, Q, consumed during a single sweep of the potential are given by
The potential of the electrode is given by E = E,
+ vt
(3) is the initial electrode po-
where Ei tential. Inasmuch as dE = vdt, Equation 2 may be rewritten in terms of E ,
or Q = -kC 21112
(5)
11-her e
The value of k is a function of potential but not of sweep rate so t h a t the product of the number of coulombs passed in the potential interval E - E, and the square root of the sweep rate is a constant for a given concentration of reactant. Thus, the product &P in potential sweep experiments with reversible couples is analogous t o the product ir112in chronopotentiometry. The equation.. for the current-potential curves for irreversible or quasireversible reactions are not of the same form as Equation 1 (2, S,1 1 ) so that Q may display a different sweep rate dependence for such cases. The work of Reiiimuth ( 1 1 ) indicates that at sufficiently high sweep rates, integration of the foot of irreversible oscillopolarographic wave< should lead t o constancy of the product Q Y instead of Q Y l 2.
For t h r reversible case n hen the only reaction occurring a t the electrode results from semi-infinite linearly diffusing reactant, Equation 5 shows that a plot of Q us. v - l f 2 should be a straight line passing through the origin. H o w v e r . if VOL. 34, NO. 13, DECEMBER 1 9 6 2
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