MECHANISMS OF THE INTERFERENCE OF CALCIUM-CHLORIDE ON ZINC IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY USING A DUAL-CAVITY PLATFORM

The dual-cavity platform allows the analyte and interferent to be vola tilized from separate cavities and therefore, in principle, allows gas -phase and condensed-phase interferences to be distinguished. In the p resence of calcium chloride, zinc chloride is formed directly in a con densed-phase interaction between analyte and interferent as well as in a gas-phase/condensed-phase reaction between zinc and HCl(g), generat ed from the hydrolysis of calcium chloride. The zinc chloride formed i s then lost in molecular form either in the pyrolysis or atomization s tage, depending on the pyrolysis temperature. Excessive background sig nals obtained in the pyrolysis stage for mixed and separated solutions of the analyte and interferent support this proposal. At elevated tem peratures, calcium chloride not only hydrolyzes to form the oxide but is also partly dehydrated to form the anhydrous chloride. When low pyr olysis temperatures are applied, gas-phase reactions or expulsion mech anisms in the atomization step appear to be likely as well.