DETERMINATION OF TRACE CONCENTRATIONS OF INDIUM IN SILICATE ROCKS BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

Trace concentrations of indium in silicate rocks were determined by graphite furnace atomic absorption spectrometry. The sample is attacked by fusion with a 1 + 1 mixture of lithium carbonate and boric acid and the melt dissolved in 1 M HCl. Indium can be separated and purified by cation exchange on cellulose phosphate and anion exchange on Bio-Rad AG 1 in HCl - NH4SCN medium. The use of a high-density graphite tube and the presence of nickel as the matrix modifier improved the sensitivity and precision of the determination by atomic absorption. For 11 silicate rock reference samples containing about 20-80 ng g-1 of indium, the relative standard deviation ranges from 3 to 13%. The results were in good agreement with the working values. The method offers selective enrichment of indium and allows the use of aqueous standard solutions of indium for the construction of calibration graphs. The sensitivity of the method is 0.0045 A per picogram of indium per microlitre.