Direct coupling of continuous hydride generation with microwave plasma torch atomic emission spectrometry for the determination of arsenic, antimony and tin

Abstract

The effect of adding hydrogen to the carrier-gas flow of a helium microwave plasma torch (MPT) discharge is evaluated in terms of plasma stability, continuum background and helium emission intensities. Also, the noise characteristics of the emission signal from the helium MPT source has been studied with special emphasis on the effect of added hydrogen. Because the MPT source can tolerate ratios of H 2/He carrier of up to 30% hydrogen, a continuous hydride-generation apparatus was coupled directly to the He MPT. The effect of the carrier and support-gas flow rates, and microwave forward power were evaluated for the determination of arsenic. The system was applied to the determination of arsenic, antimony and tin by atomic emission spectrometry. Detection limits (3σ) of 3.2, 5.9 and 2.5 ng ml −1 were obtained for As, Sb and Sn, respectively, when a plasma power of 200 W was used. Linear dynamic ranges were over 3 orders of magnitude for the three elements. The argon MPT source accepts the introduction of hydrogen up to carrier-gas ratios of 20%, but yields a detection limit for As of only 65 ng ml −1.