Determination of zinc (II), cadmium (II), lead (II) and copper (II) in common and balsamic vinegar by stripping chronopotentiometry

A method for the determination of zinc (II), cadmium (II), lead (II) and copper (II) in common and balsamic vinegar by stripping chronopotentiometry 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 90-98% for zinc (II), 91- 97% for cadmium (II), 94-98% for lead (II) and 93-97% for copper (II) were obtained from a sample spiked at different levels. The detection limits were 10.6 ng g-1 for zinc (II), 2.2 ng g-1 for cadmium (II), 3.4 ng g-1 for lead (II) and 4.2 ng g-1 for copper (II) and the relative standard deviations (mean of nine determinations) were 4.8, 6.5, 3.2 and 5.3%, respectively. Results obtained on commercial common and balsamic vinegars were not significantly different from those obtained by atomic absorption spectrometry