Evaluation of non-chromatographic approaches for speciation of extractable As(III) and As(V) in environmental solid samples by FI-HGAAS

Non-chromatographic speciation approaches have been developed for determination of water-soluble and phosphate-exchangeable As(III) and As(V) in certified reference materials of coal fly ash and sediments by FI-HGAAS. A 2IV6–2 fractional factorial design was employed for screening optimisation of the flow injection manifold. A simple two-stage sequential extraction protocol involving deionized water and a phosphate buffer as extractants was employed. Determination of both oxidation states of As in the extracts could be accomplished following arsine generation under different reaction conditions, namely, (i) selective determination of As(III) in citric acid medium or using soft generation conditions (i.e. low HCl and NaBH4 concentrations); (ii) determination of total As in each extract using thioglycollic acid as reaction medium or after pre-reduction of As(V) to As(III) with a KI+ascorbic acid mixture. The As(V) content was estimated by difference between both measurements. Reaction conditions were previously optimised and analytical parameters in each reaction medium were established. Overall, the extractable As content was less than 5% in sediment and fly ash CRMs. The LOD of As was around 0.07 μg l−1 for As(III) determination, and 0.06 μg l−1 for total As determination after prereduction. Liquid chromatography coupled to atomic fluorescence spectrometry with post-column hydride generation was used for comparison.