Determination of lead (II) and cadmium (II) in hard and soft wheat by derivative potentiometric stripping analysis

A method for the determination of lead (II) and cadmium (II) in hard and soft wheat by derivative potentiometric stripping analysis is described. The metal ions were concentrated as their amalgams on the glassy carbon surface of a working electrode that was previously coated with a thin mercury film, and then stripped by a suitable oxidant. Potential and time data were digitally converted into dt dE(-1), and E was plotted vs. dr dE(-1), thus increasing both the sensitivity of the method and resolution of the analysis. Quantitative analysis was carried out by the method of standard additions; a good linearity was obtained in the range of concentrations examined. Recoveries of 94-100% for lead (II) and of 91-98% for cadmium (II) were obtained from hard wheat spiked at different levels. The detection limits were 9.4 ng g(-1) for lead (II) and 6.5 ng g(-1) for cadmium (II) and the reproducibilities (mean of nine determinations) were 3.4 and 3.6%, respectively. Results obtained on commercial hard and soft wheats were not significantly different from those obtained by inductively coupled plasma atomic emission spectrometry. (C) 2000 Elsevier Science B.V. All rights reserved.