Square Wave Anodic Stripping Determination of Silver Using a Carbon Paste Electrode Modified with a Strong Acid Ion-Exchanger

Abstract

A chemically modified carbon paste electrode was developed for the determination of silver by incorporating the ion-exchanger Dowex 50 W × 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 µg L⁻¹ to 0.8 mg L⁻¹ with a detection limit of 0.27 µg L⁻¹. The dynamic range could be extended up to 2.5 mg L⁻¹ (from 0.92 µg L⁻¹ to 2.5 mg L⁻¹) with 20 min of preconcentration. The method showed good tolerance for Cu²⁺, Fe³⁺, Cd²⁺, Zn²⁺, Pb²⁺, and Au³⁺. Interference from Hg²⁺ up to 5 mg L⁻¹ was avoided by masking with EDTA in the preconcentration step.

Keywords:

• Carbon paste electrode
• Silver analysis
• Square wave anodic stripping voltammetry
• Modified carbon paste.

Acknowledgment

The financial support of the Secretaría de Ciencia y Técnica (Project Nr. 9001) of the Universidad Nacional de San Luis, Argentina, is gratefully acknowledged.