Wall-to-platform migration in electrothermal atomic absorption spectrometry Part 1. Investigation of the mechanism of chloride interference on thallium

Abstract

In wall-to-platform migration, the sample aliquot is pipetted onto the graphite furnace wall. Heating of the furnace then causes migration of the analyte from the wall to the platform. This technique permitted the atomic absorption signal for 1 ng of thallium to be separated in time from the background absorption signal from 10 μg of a sodium chloride matrix. This precluded interference through a gas-phase reaction or through expulsion loss of analyte, since they would require analyte and matrix to be present in the gas phase at the same time. Hence, it was concluded that interference by chloride occurred in the condensed phase. A refinement of wall-to-platform migration, called the “two-platform method”, permitted an examination of the temperature dependence of analyte migration from the wall to the platform, and hence the stage of furnace heating when interference occurred. This showed that interference occurred between condensed-phase species, at temperatures from 500 to 700°C, during the pyrolysis stage of the furnace heating cycle.