Mechanisms of the interference of calcium chloride on zinc in graphite furnace atomic absorption spectrometry using a dual-cavity platform

Abstract

The dual-cavity platform allows the analyte and interferent to be volatilized from separate cavities and therefore, in principle, allows gas-phase and condensed-phase interferences to be distinguished. In the presence of calcium chloride, zinc chloride is formed directly in a condensed-phase interaction between analyte and interferent as well as in a gasphase/condensed-phase reaction between zinc and HCI(g), generated from the hydrolysis of calcium chloride. The zinc chloride formed is then lost in molecular form either in the pyrolysis or atomization stage, depending on the pyrolysis temperature. Excessive background signals obtained in the pyrolysis stage for mixed and separated solutions of the analyte and interferent support this proposal. At elevated temperatures, calcium chloride not only hydrolyzes to form the oxide but is also partly dehydrated to form the anhydrous chloride. When low pyrolysis temperatures are applied, gas-phase reactions or expulsion mechanisms in the atomization step appear to be likely as well.