Use of sodium tungstate as a permanent chemical modifier for slurry sampling electrothermal atomic absorption spectrometric determination of indium in soils

Abstract

A number of chemical modifiers have been assessed for the direct determination of indium in soils using electrothermal atomic absorption spectrometry and slurry sampling. The best results were obtained when the graphite atomizer was impregnated with sodium tungstate, which acts as a permanent chemical modifier. Slurries were prepared by suspending 100 mg sample in a solution containing 1% (v/v) concentrated nitric acid and 10% (v/v) concentrated hydrofluoric acid and then 15-μL aliquots were directly introduced into the atomizer. Standard indium solutions prepared in the suspension medium in the range 4–80 μg L^-1 indium were used for calibration. The relative standard deviation for ten consecutive measurements of a 40 μg L^-1 indium solution was 2.8%. The limit of detection in soils was 0.1 μg g^-1. The reliability of the procedures was confirmed by analysing two standard reference materials and by using an alternative procedure.