DETERMINATION OF CHROMIUM(III) AND CHROMIUM(VI) BY ELECTROTHERMAL ATOMIZATION ATOMIC-ABSORPTION SPECTROMETRY FOLLOWING COPRECIPITATION WITH GALLIUM(III) PHOSPHATE

Gallium(III) phosphate coprecipitates quantitatively 0.2-7.5 mu g of chromium(III) from 100 to 500 cm(3) of a sample solution at pH 4.5-6.0. Although chromium(VI) is hardly coprecipitated with gallium(III) phosphate, it can be collected as chromium(III) after reduction by hydroxylamine. The calibration curve is linear from 8 to 300 ng cm(-3) for chromium. The detection limit (signal/noise=2) is 0.11 ng cm(-3) of chromium(III) or chromium(VI) in 500 cm(3) of the initial sample solution.