Mechanism and removal of halide interferences in the determination of metals by atomic absorption spectrometry with electrothermal atomization

The effects of halides on the graphite-furnace atomic absorption determination of Al, Be, Sr, Cr, Mn, Ni, Co, Cu, Zn, Pb, Cd and Ag have been studied from the view-point of chemical reactions in solution, particularly in terms of the hard and soft acid and base concept. The harder halides interfere strongly with the harder metals, and the softer halides with the softer metals. This indicates that the halide interferences arise initially from metal—halide complex formation in solution; this was confirmed by an examination of halide concentration effects on the atomic absorption signal. The ammonium salt of EDTA is a most suitable additive for removal of halide interferences, because it prevents metal—halide complexation, and readily volatile ammonium halide is produced.