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High performance liquid chromatography coupled to ICP-AES detection provides a rapid, reliable and sensitive method for arsenic speciation. The separation of As(III), As(V), DMA and MMA was achieved with ion exchange chromatography coupled to an axially-viewed sequential ICP-AES. After optimization of the chromatographic parameters (pH and concentration of the mobile phase), a careful study of the interface was conducted. Five nebulizers associated to three spray chambers were tested. Response of the ICP to each arsenic species was strongly affected by the selection of the nebulizer and spray chamber, however similar responses were obtained for each arsenic species. Best signal-to-noise ratios were obtained by using a microconcentric nebulizer and a cyclone spray chamber and did not affect the chromatographic resolution. Detection limits better than 10 microg L(-1) were obtained for As(III), DMA, MMA and 20 microg L(-1) for As(V), which is a significant improvement over previously published results.

Self-absorption effects leading to curvatures of the upper part of calibration graphs were investigated in multichannel detection ICP-AES. A dual view Optima 3000 ICP system was used to enable the simultaneous determination of 38 lines for both radial and axial viewing. Resonance and non-resonance lines were selected for both atomic and ionic lines. The concentrations of 22 standards were in the range 0.1-100 mg L(-1) and two sets of operating conditions, namely power and carrier gas flow rate, were used to evaluate their influence. It was found that these two conditions, and in particular the carrier gas flow rate, play a major role in self-absorption effects. Except for strongly absorbing lines, it was possible, under suitable conditions, to reduce or to suppress differences between self-absorption effects in radial and axial viewing, enabling extension of the range of linearity of axial viewing to higher concentrations. A diagnostic tool, based on emission line ratios, is proposed for detection of self-absorption. A calibration procedure is given for strongly absorbing lines affected by self-absorption even when operating conditions were optimized.

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