Hydride generation-pervaporation-atomic fluorescence detection prior to speciation analysis of arsenic in dirty samples

Abstract

A flow injection-pervaporation method for the continuous derivatisation and determination by atomic fluorescence spectrometry is proposed for the first time in order to speciate As as As^III and As^V. The sample at different pHs was injected into a 6 M HCl stream and then mixed with 0.5% or 0.05% m/v NaBH₄. The reactant mixture was transported to the lower chamber of a pervaporator from which the arsine generated evaporated to the air gap between the liquid and the membrane, diffused through the latter and was swept out of the acceptor chamber by a hydrogen–argon stream into the chemically generated hydrogen diffusion flame. An auxiliary H₂ flow was necessary to support the flame. The linear ranges of the calibration curves for As^III and As^V were from pg ml⁻¹ to ng ml⁻¹, with correlation coefficients, r², better than 0.99. For As^III, the reproducibility and repeatability, expressed as relative standard deviation, were 3.0% and 1.1%, respectively, and for As^V were 3.2% and 1.3%, respectively. The detection and quantification limits were 0.42 ng ml⁻¹ and 0.61 ng ml⁻¹ for As^III and AS^V, respectively. The method thus developed was applied to ‘dirty’ aqueous samples with solid particles in suspension, without prior filtration, and provided a sampling frequency of 12 h⁻¹.