Determination of arsenic in geological materials by x-ray fluorescence spectrometry after solvent extraction and deposition on a filter.
Rock, soil, or sediment samples are decomposed with a mixture of nitric and sulphuric adds. After reduction from arsenic(V) with ammonium thiosulphate, arsenic(III) is extracted as the chlorocomplex into benzene from a sulphuric-hydrochloric acid medium. The benzene solution is transferred onto a filter-paper disc impregnated with a solution of sodium bicarbonate and potassium sodium tartrate, and the benzene allowed to evaporate. The arsenic present is determined by X-ray fluorescence. In a 0.5-g sample, 1-1000 ppm of arsenic can be determined. The close proximity of the lead Lalpha peak (2theta 48.73 degrees ), to the arsenic Kalpha peak (2theta 48.83 degrees ) does not cause any interference, because lead is not extracted under the experimental conditions. Arsenic values obtained are in agreement with those reported for various reference samples.
Hubert
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U.S. Geological Survey, Box 25046, Denver, CO 80225, U.S.A.