THE USE OF OPTICAL-EMISSION SPECTROMETRY WITH MICROWAVE-INDUCED PLASMA (MIP) DISCHARGES IN A SURFATRON COMBINED TO DIFFERENT TYPES OF HYDRIDE GENERATION FOR THE DETERMINATION OF ARSENIC

The stability and analytical figures of merit of argon microwave induced plasma (MIP) discharges in a surfatron as sources for optical emission spectrometry (OES) are described. These MIPs have been used for the determination of arsenic after hydride generation. They could cope with the excess of hydrogen developed during the hydride generation step and thus not necessitated an isolation of the hydrides before releasing them into the MIP. Two methods for the generation of the volatile AsH3 were applied. First a micro method was used with solid NaBH4 on which 10 mul of the acidified sample solution is transferred. Its capabilities were compared to those of continuous hydride generation using a 5% (w/w) NaBH4-solution and continuous liquid removal in a flow cell. Both methods were optimized for an argon MIP operated at a power of 120-160 W and gas flows of 20 1/h Ar. In the case of solid NaBH4 the detection limit for As has been found to be 1.0 mug/ml (10 ng) and with the flow cell hydride generation 50 ng/ml. The calibration curves are linear over three orders of magnitude. Interferences caused by Sb, Fe, Sn and NaCl were investigated. No interferences occurred for Sb up to an interferent concentration of 250 mug/ml. The presence of Fe causes a significant depression of the As signal whereas an increase of the As signal was observed in the case of Sn. High NaCl concentrations did not influence the As signals when using continuous hydride generation, but had a great influence when using solid NaBH4.