A systematic approach to faradaic current, charging current and phase angle measurement by digital alternating current polarography

A. M. Bond, I. D. Heritage

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Abstract

In microprocessor-based digital ac polarography, the simultaneous measurement of total alternating current polarograms at 10° phase angle intervals allows the calculation of both the faradaic and charging current components of the experiment as well as their phase-angle relationship to the applied potential. The data evaluation procedure is based upon extrapolation of the background current at potentials removed from the faradaic process so as to enable the charging current to be calculated in the presence of the faradaic current. The faradaic current can then be calculated by subtraction of the charging current. Curve fitting of the separated faradaic and charging current functions to an equation of the kind Y = A sin (X + φ), where φ is the phase angle, enables interpolated phase angles for the faradaic response to be calculated with an accuracy of better than 1°. Data are presented for the process [Fe(ox)3]3- + e- ⇌ [Fe(ox)3]4- (ox = oxalate) at a mercury electrode and provide a frequency-independent phase angle of (45 ± 1)0 as expected theoretically for a reversible process. The two-electron reduction of copper(II) in 1 M NaNO3 to produce a copper amalgam exhibits the theoretical frequency-dependent phase angle of less than 45° expected for a quasi-reversible process. The microprocessor-based digital ac method of phase-angle measurement is considered to be superior to conventional analog approaches, but not as accurate as the Fast Fourier Transform method developed by Smith and co-workers with more elaborate and expensive expensive laboratory computer-based instrumentation.

Original languageEnglish
Pages (from-to)35-44
Number of pages10
JournalJournal of Electroanalytical Chemistry
Volume222
Issue number1-2
DOIs
Publication statusPublished - 8 May 1987

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