Determination of total arsenic in soils by differential-pulse cathodic stripping voltammetry

Abstract

A procedure which permits the determination of total arsenic in soils using differential-pulse cathodic stripping voltammetry at a hanging mercury drop in the presence of copper after the acid digestion of solid samples in a closed-vessel microwave digester was developed. Optimized conditions include accumulation potential –0.5 V, accumulation time 120 s, 0.05 mol l^–1 of KI to reduce As^V to As^III, 10 µg ml^–1 of copper and both 3.8 mol l^–1 HCl and 0.24 mol l^–1 NaHCO₃ as electrolyte. The detection limit was 50 pg ml^–1 and the reproducibility was 3.8% intra-day and 4.5% inter-day for 10 determinations at a concentration of 2.6 ng ml^–1. The method was applied to a reference certified soil sample, obtaining a relative error of 0.7%. Results for 12 soil samples from a zone of the Basque Country were compared with those obtained by hydride generation atomic absorption spectrometry.