Simultaneous ultratrace determination of platinum and rhodium by cathodic stripping voltammetry

A highly sensitive, catalytic adsorptive stripping voltammetric procedure at the hanging mercury drop electrode for the simultaneous determination of ultratraces of platinum and rhodium in electrolyte solutions has been evaluated. Optimal conditions were found to be: first accumulation potential 0 V (vs. Ag/AgCl), second accumulation potential −0.8 V, first preconcentration time 90 s, second preconcentration time 120 s, scan rate 20 mV s−1. The response of the system was found to be linear in a range of platinum concentrations up to 6 ng l−1 and for rhodium up to 0.5 ng l−1. The detection limit was 21 pg l−1 for platinum and 5.6 pg l−1 for rhodium. The effect of various possible interferences from other metal ions was also studied. With the exception of zinc (whose influence was studied in more detail), no significant interferences were observed. The method was successfully applied to the determination of traces of Pt and Rh in real environmental samples (spruce shoots) after high pressure digestion.