Deposition time
In all the analyzed wine samples, the concentration of cadmium was lower than 1 ng/mL, lead was found in the range of 4 to 250 ng/mL and copper was higher than 50 ng/mL. Figure 2 demonstrates the influence of the deposition time on the peak area of Cd, Pb, and Cu. For cadmium and lead, a linear correlation between both parameters was observed. Due to the low solubility of copper in mercury and high natural concentration of copper in wine samples some problems were encountered. With an increase in the deposition time, two peaks in the copper
stripping region with different shapes were observed.
If the mercury film was thin, copper would not reduce on the electrode surface and only a small oxidation peak was observed. With an increase in the deposition time, better
crystallization of the copper occurred on the electrode surface or in the mercury film, and a significantly larger copper stripping signal was observed with a good linear correlation.
The amount of reduced copper depended not only on the deposition time but also on the copper concentration in the sample.
To get good analytical results for copper, it was necessary to use longer deposition time
(> 4 min) [8].