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 Lα peak (2θ 48.73°), to the arsenic Kα peak (2θ 48.83°) 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.