Square wave anodic stripping determination of silver using a carbon paste electrode modified with a strong acid ion-exchanger

A chemically modified carbon paste electrode was developed for the determination of silver by incorporating the ion-exchanger Dowex 50 W x 12 into a conventional graphite-Nujol oil paste. Silver(I) was accumulated at the electrode surface from solutions of the sample under open circuit conditions, then reduced at constant potential in a separate 0.1 M HNO3 solution and finally determined by square wave (Osteryoung) anodic stripping voltammetry. The influence of paste composition, acummulation/reduction time, possible interferences and other experimental variables on the height and shape of the anodic peak was examined in detail. For 5 min of accumulation, the linear range was from 1.62 mug L-1 to 0.8 mg L-1 with a detection limit of 0.27 mug L-1. The dynamic range could be extended up to 2.5 mg L-1 (from 0.92 mug L-1 to 2.5 mg L-1) with 20 min of preconcentration. The method showed good tolerance for CU2+, Fe3+, Cd2+, Zn2+, Ph2+, and Au3+. Interference from Hg2+ up to 5 mg L-1 was avoided by masking with EDTA in the preconcentration step.