Determination of chromium in biological fluids by electrothermal atomic absorption spectrometry using wall, platform and probe atomization from different graphite surfaces

Abstract

Different atomization techniques (wall, platform and probe) and graphite surfaces [electrographite, pyrolytic coated graphite (pyrocoated) and totally pyrolytic graphite] for the determination of chromium in water, urine and serum samples by electrothermal atomic absorption spectrometry have been investigated. Water and urine can be analysed without dilution, while serum was diluted (1 + 1) with 0.2% Triton X-100 in 0.1% nitric acid. Wall atomization from pyrocoated graphite cuvettes provided the best analytical performance and the most convenient temperature programmes for all sample types under study. Magnesium plus calcium nitrate mixtures proved to be the most convenient chemical modifier for the determination of chromium in aqueous solutions. Detection limits are lowered from 0.07 to 0.04 µg l–1 of chromium in the presence of such a modifier. Only slightly better performance was observed for serum samples, however. In urine samples, the addition of a chemical modifier did not significantly change the detection limit observed in its absence (0.05 µg l–1). The detection limits estimated for optimum conditions (pyrocoated tube, wall atomization and optimized temperature programme) were 0.04 µg l–1 for water, 0.22 µg l–1 for undiluted serum and 0.05 µg l–1 for urine (without an external chemical modifier in this latter case). Within-run precisions were around 0.8–5% in all cases. The recovery studies carried out, both in the presence and in the absence of modifier, using optimized temperature programmes, have shown the accuracy of the proposed procedures.