Direct Determination of Arsenic in Sea-water by Continuous-flow Hydride Generation Atomic Fluorescence Spectrometry

Abstract

A highly sensitive and simple procedure was developed for the direct determination of total As in sea-water samples by hydride generation atomic fluorescence spectrometry. The method involves the generation of arsenic hydride from sea-water samples, diluted with HCl to a final HCl concentration of 2 mol l^–1, which were merged with a reducing solution, viz., 3% m/v NaBH₄. The sample and NaBH₄ were pumped at flow rates of 6.0 and 1.3 ml min^–1, respectively, and allowed to react in a 200 cm×0.8 mm id reaction coil. The evolved arsenic hydride was removed using an argon flow rate of 400 ml min^–1 and passed to a hydrogen diffusion flame where the atomic fluorescence of As was measured at 193.7 nm. With the proposed procedure a detection limit of 5.0 ng l^–1 was achieved. The repeatability of the determination varied between 1.5 and 4.0%. The accuracy was confirmed by the analysis of two sea-water reference materials (NASS-4 and CRM-403) and by recovery studies on natural samples spiked with known concentrations of As^III and As^V. The proposed method was successfully applied to the determination of As in several sea-water samples. The number of samples that can be analysed is 40 per hour.