MECHANISMS OF MAGNESIUM-CHLORIDE INTERFERENCES ON ZINC IN ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY USING A DUAL CAVITY PLATFORM

The mechanism of interference due to magnesium chloride on the determi nation of zinc in electrothermal atomic absorption spectrometry has be en investigated using a dual cavity platform which has two separate ca vities instead of one. It allows the analyte and interferent to be int roduced at separate locations on the platform without mixing in the co ndensed phase; therefore, in principle, gas-phase and condensed phase interferences can be distinguished. In the presence of magnesium chlor ide, zinc chloride is formed both in the condensed phase and upon reac tion between analyte species and HCl(g) formed from the hydrolysis of magnesium chloride, and is lost in molecular form during the pyrolysis or early in the atomization steps. At low pyrolysis temperatures, whe re magnesium chloride is not significantly hydrolysed but rapidly deco mposes during the atomization step, expulsion of analyte from the furn ace together with matrix gases and/or gas-phase reaction between zinc atoms and chlorine in this step are responsible for signal depression.