Potential of the hydride generation technique coupled to inductively coupled plasma optical emission spectrometry for non-chromatographic As speciation

Abstract

A systematic study of hydride generation (HG) in the sample introduction step combined with inductively coupled plasma optical emission spectrometry (ICP OES) for non-chromatographic As speciation from solutions of As(III), As(V), dimethylarsinate (DMA) and monomethylarsonate (MMA) is presented. Hydrides were generated in the reaction with NaBH₄ in the acidic medium using a continuous flow system with a gas–liquid phase separation directly coupled with ICP. Optimization of the HG operational parameters was performed to improve the detectability of As. The different reactivities of the examined As species under various reaction conditions [in terms of the type and concentration of acids (HCl, acetic and citric), buffers (acetate and citrate), the NaBH₄ concentration and presence of pre-reducing agents (KI-ascorbic acid, thiourea-ascorbic acid and L-cysteine)] were used for selective generation of their individual hydrides. The relationship among As(III), As(V), DMA and MMA signals under different reduction conditions was studied and discussed. Considering all favorable pre-reducing and HG reaction conditions, five speciation procedures (SPs) for species-selective HG of As in one solution, including SP1 for [As(III)], SP2 for [As(III) + DMA], SP3 for [As(III) + As(V) + MMA], SP4 for [DMA + MMA] and SP5 for [As(III) + As(V) + DMA + MMA], were evaluated. Differentiation between As(III), As(V), DMA and MMA along with distinguishing between species having the same nature, i.e. i-As [As(III,V)] and o-As (DMA, MMA), was achieved. By combining the analytical responses obtained with HG-ICP OES, the experimental protocols for determination and non-chromatographic speciation (both individual and operational) of hydride-active As species were proposed.