DETERMINATION OF TOTAL ARSENIC IN SOILS BY DIFFERENTIAL-PULSE CATHODIC STRIPPING VOLTAMMETRY

A procedure which permits the determination of total arsenic in soils using differential-pulse cathodic stripping voltammetry at a hanging m ercury drop in the presence of copper after the acid digestion of soli d samples in a closed-vessel microwave digester was developed. Optimiz ed 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 mu g ml(-1) of copper and both 3.8 mol l(-1) HCl and 0.24 mol l(-1) NaHCO3 as elec trolyte. 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 conce ntration of 2.6 ng ml(-1). The method was applied to a reference certi fied soil sample, obtaining a relative error of 0.7%, Results for 12 s oil samples from a zone of the Basque Country mere compared with those obtained by hydride generation atomic absorption spectrometry.