EFFECT OF COBALT CHLORIDE ON THE ATOMIZATION OF ZINC IN ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

The effect of cobalt chloride oh zinc at different pre-treatment tempe ratures has been investigated by using a dual cavity platform, which m akes differentiation between gas-phase and condensed-phase interferenc es possible. When the analyte and interferent are separated on the dua l cavity platform, condensed-phase interferences disappear whereas gas -phase interferences continue to affect the sensitivity of the analyte . The effect of the addition of nitric acid on the atomic absorption s ignals of the interferent under the atomization conditions of the anal yte, the atomic absorption and background signals for the analyte, the interferents and their mixed or separated solutions obtained in the a tomization and pre-treatment steps, and thermal pre-treatment of the i nterferent at different temperatures before pipetting the analyte into the same cavity, served to elucidate the interference mechanism. The dominant interference mechanism is the formation of volatile zinc chlo ride upon reaction between the analyte and the interferent at low temp eratures, which js expelled out of the tube by the gaseous hydrogen ch loride generated in large amounts during the thermal hydrolysis of cob alt chloride hexahydrate. A condensed-phase-gas-phase reaction between the gaseous hydrogen chloride and the analyte may causes the formatio n of zinc chloride as well. Gas-phase reaction and/or expulsion mechan isms seem plausible but their effects are not very pronounced.