Arsenic preconcentration viasolid phase extraction and speciation by HPLC-gradient hydride generation atomic absorption spectrometry

Abstract

A novel method for arsenic speciation is developed by interfacing solid phase preconcentration-liquid chromatography (LC) separation-gradient hydride generation (GHG)-quartz flame atomic absorption spectrometry (QFAAS). A MnO₂ mini-column is used to preconcentrate the arsenic species of As(III), As(V), MMA and DMA, during which process, As(III) is converted to As(V)viaoxidation by MnO₂, while other species remain unchanged. The recovery of As(V) (i.e., the total amount of arsenate and arsenite in the original sample), MMA and DMA from the MnO₂ mini-column is facilitated by tetramethylammonium hydroxide (TMAH). After LC separation with C30 columns, arsenic species in the eluate are subject to gradient hydride generation with detection by QFAAS. On the other hand, cellulose fibre selectively adsorbs the chelating complex between As(III) and ammonium pyrrolidine dithiocarbamate (APDC). After elution with HNO₃, As(III) in the original sample is quantified by graphite furnace atomic absorption spectrometry (GFAAS), and the amount of As(V) is obtained by subtraction. A sample volume of 2.0 mL derives enrichment factors of 14.0–19.2 for the arsenic species. By injecting 20 μL of eluate into the LC system (the eluate of As(III)-PDC complex is injected into the GFAAS), detection limits of 0.019, 0.33, 0.39, 0.62 μg L⁻¹ are obtained for As(III), As(V), MMA and DMA respectively. RSDs of less than 4.2% are achieved at the level of 2 μg L⁻¹ for As(V), MMA, DMA and 1 μg L⁻¹ for As(III). The procedure is evaluated by speciating arsenic in snow water and Hijiki samples.