Determination of cadmium and lead in the low ng/l range by stripping potentiometry employing medium exchange in batch mode and multiple stripping in a hanging stripping medium drop.

ABSTRACT

A novel three-in-one electrode assembly, permitting medium exchange under a controlled potential in batch mode by exploiting electrolytic conductance through a drop hanging under the electrode, has been used for the simultaneous determination of cadmium(II) and lead(II) at trace levels. Potentiostatic reduction and amalgamation of these ions are carried out in the sample and the subsequent stripping, in the stripping potentiometry mode, in a drop of a suitable medium. Several such media have been investigated, a mixture of 2.5M acetic acid and 7.5M ammonium acetate having been found to be the most suitable with respect to sensitivity, potential resolution and trace metal purity. The quiescent conditions in the drop of medium facilitated multiple stripping and thus increased sensitivity. Detection limits for cadmium(II) and lead(II) were found to be around 0.5 ng/l. (5 and 2.5pM) for an electrolysis time of 10 min. The relative precision at the concentration level 20 ng/l. was 6.4% for cadmium and 5.4% for lead. The procedure has been used for the determination of cadmium(II) and lead(II) in reference seawater samples.