EVALUATION OF CONTINUOUS HYDRIDE GENERATION COMBINED WITH HELIUM AND ARGON MICROWAVE-INDUCED PLASMAS USING A SURFATRON FOR ATOMIC-EMISSION SPECTROMETRIC DETERMINATION OF ARSENIC, ANTIMONY AND SELENIUM

The direct coupling of continuous hydride generation with both Ar and He microwave induced plasmas (MIP) sustained in a surfatron has been o ptimized for the simultaneous determination of arsenic, antimony and s elenium with atomic emission spectrometry. While a discharge tube of q uartz was found suitable for the Ar plasma, the use of an Al2O3 tube l ed to improved performance of the He plasma. The He MIP was found to b e less tolerant to the introduction of hydrogen than the Ar MIP, and c orrespondingly the hydride generation should be operated at a lower fl ow rate of 0.5% NaBH4 solution. The introduction of the H2O vapour pro duced during hydride generation into both discharges was found to grea tly decrease the sensitivities and to degrade the measurement precisio n. It could be effectively removed with trapping by concentrated H2SO4 . The detection limits (3 sigma) for As, Sb and Se are 1, 0.4 and 1 ng ml(-1) with the Ar MIP, and 2, 0.3 and 6 ng ml(-1) with the He MIP, r espectively. The calibration curves are linear over three decades of c oncentration. The mutual interferences from As(III), Sb(III), Se(IV), Bi(III) and Sn(IV) were found to be negligible at interferent concentr ations below 1 mu g ml(-1) and in most cases the tolerable interferent concentrations are up to 20 mu g ml(-1). The proposed method has been applied to determination of As, Sb and Se in tea samples at mu g g(-1 ) levels.