Determination of cadmium (II) and lead (II) in whole and skim milk by stripping chronopotentiometric analysis

A method for the determination of cadmium (II) and lead (II) in whole and skim milk by stripping chronopotentiometric analysis is described. The metal ions were concentrated as their amalgams on a glassy carbon 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. dt dE-1, thus increasing both 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 cadmium (II) and of 91-98% for lead (II) were obtained from a sample spiked at different levels. The detection limits were 4.4 ng g-1 for cadmium (II) and 8.6 ng g-1 for lead (II) and the relative standard deviations (mean of nine determinations) were 4.1 and 5.6%, respectively. Results obtained on commercial whole and skim milk were not significantly different from those obtained by inductively coupled plasma atomic emission spectrometry.