Speciation of arsenic by hydride generation–atomic absorption spectrometry (HG–AAS) in hydrochloric acid reaction medium

The effects on the absorbance signals obtained using HG–AAS of variations in concentrations of the reaction medium (hydrochloric acid), the reducing agent [sodium tetrahydroborate(III); NaBH4], the pre-reducing agent (l-cysteine), and the contact time (between l-cysteine and arsenic-containing solutions) for the arsines generated from solutions of arsenite, arsenate, monomethylarsonic acid (MMA), and dimethylarsenic acid (DMA), have been investigated to find a method for analysis of the four arsenic species in environmental samples. Signals were found to be greatly enhanced in low acid concentration in both the absence (0.03–0.60 M HCl) and the presence of l–cysteine (0.001–0.03 M HCl), however with l-cysteine present, higher signals were obtained. Total arsenic content and speciation of DMA, As(III), MMA, and As(V) in mixtures containing the four arsenic species, as well as some environmental samples have been obtained using the following conditions: (i) total arsenic: 0.01 M acid, 2% NaBH4, 5% l-cysteine, and contact time<10 min; (ii) DMA: 1.0 M acid, 0.3–0.6% NaBH4, 4.0% l-cysteine, and contact time <5 min; (iii) As(III): 4–6 M acid and 0.05% NaBH4 in the absence of l-cysteine; (iv) MMA: 4.0 M acid, 0.03% NaBH4, 0.4% l-cysteine, and contact time of 30 min; (v) As(V): by difference. Detection limits (ppb) for analysis of total arsenic, DMA, As(III), and MMA were found to be 1.1 (n=7), 0.5 (n=5), 0.6 (n=7), and 1.8 (n=4), respectively. Good percentage recoveries (102–114%) of added spikes were obtained for all analyses.