Effect of high salt concentrations on the determination of arsenic and selenium by flow injection hydride generation electrothermal atomic absorption spectrometry

In the determination of arsenic and selenium by flow injection hydride generation ETAAS, the presence of up to 20% sodium chloride enhanced the signals for 20 mu g l(-1) arsenic and selenium by up to 28%, The enhancement was obtained with a variety of gas-liquid separators. A systematic study of the possible causes of the signal enhancement in the determination of selenium was undertaken, from which it was concluded that the effect originated in the processes responsible for the distribution of the hydrogen selenide between the solution and gas phases. Processes related to the transport of the analyte from the gas-liquid separator and the trapping of the analyte on the interior of the atomizer were not affected by the presence of dissolved salts. As sodium was found to be transported to the atomizer, it was deduced that aqueous aerosol was deposited in the atomizer, although the quantities were irreproducible, The enhancement could be eliminated by increasing the borohydride concentration. However, with the small volume gas-liquid separator, this latter approach was limited because of carry-over of liquid to the atomizer. The effect could be compensated for by adding up to 40% m/v of salt to the borohydride reagent.