Determination of heavy metals in milk and fermented milk products by potentiometric stripping analysis with constant inverse current in the analytical step.

A simple and rapid method for the direct determination of cadmium, lead and copper in milk and fermented milk products by potentiometric stripping analysis (PSA) with oxygen as an oxidant and with inverse current imposed through the stripping step is described. For the more selective metals determination a samples pretreatment by the microwave acid extraction was applied. Due to the significant increase of the modified technique sensitivity, the detection limits of 0.30, 1.7 and 3.8 μg/l were obtained, for cadmium, lead and copper, respectively. The method accuracy was confirmed by analysing the standard reference material (SRM 1577 b). The contents of cadmium, lead and copper in milk samples were in the range of 2.13-4.82, 54.3-95.2 and 112.2-124.7 μg/kg, respectively, whereas in the samples of fermented milk products in the range of 6.30-24.1, 210.1-463.6 and 260.0-320.7 μg/kg, respectively.