Simultaneous determination of iron(II) and iron(III) at micromolar concentrations by differential pulse polarography

Abstract

normalized Ai, is 75% maximum) and minimum peak width (W,p is 124/n mV compared to its minimum value of 90/n mV). A value of IAEl = 50/n mV (at T = 25 "C) is thus recommended for analytical purposes. Of course in the solution of analytical problems where n may not be known, or where a multicomponent mixture of species with different n values or similar values of Ellz is present, the pulse height should be optimized experimentally.Analytical figures of merit such as detection limits have not been determined in this study. However, the theoretical analysis of both faradaic and capacitative currents and the excellent agreement of experiment with theory at parts-permillion concentration levels without background subtraction suggest that this technique will be competitive with DP voltammetry for analytical purposes. It should be especially useful in nonideal cases where interferences due to electrode passivation, adsorption phenomena, or electrode "conditioning" may be reduced or eliminated by judicious choice of the time and potential parameters of the experiment. At the same time, the technique should be useful for quantitative mechanistic studies of these same phenomena. With the experimental verification of the theory for the reversible case above, the foundation is laid for application of the technique to such cases.

Trace Iron Determination by Cyclic and Multiple Square-Wave Voltammetry at Nafion Coated Electrodes. Applicationto Pore-Water Analysis

“…A differential pulse polarographic method for Fe(II) and Fe(III) determination at mM concentration ranges was also developed; it took advantage of nonaqueous solvents both for the extraction and electrochemical determination of the analyte(s) [24]. In spite of its redox speciation ability and interesting sensitivity, because of the complexity of the procedures this method does not seem particularly suitable for quick analysis and for``in ®eld'' determinations.…”

Integration of differential pulse voltammograms for concentration measurements

“…This would imply a mobile equilibrium (rapid dissociation and association), at least at low pH values. On the other hand, Wheelwright et al (7) estimated stability constants of rare earth-EDTA complexes polarographically by measuring the Cu displaced upon addition of rare earth to solutions equimolar in Cu and EDTA. Their values agreed with potentiometric estimates and indicated that uncomplexed Cu was accurately measured polarographically in the presence of CuEDTA complexes.…”

“…Quantitative analysis with differential pulse polarography or voltammetry is usually done by measuring the differential current at its maximum and comparing this to a calibration curve (5)(6)(7). However, in several reports it has been demonstrated that small perturbations in the resistance of the electrochemical cell, or in the degree of electrochemical or chemical reversibility, can greatly affect both the differential current amplitude and its location on the applied potential axis (5, 6, [8][9][10].…”