Determination of indium in rocks by substoichiometric radioisotope dilution analysis

Rocks containing 10–140 ng of indium per g are decomposed with hydrofluoric and nitric acids in the presence of ¹¹⁴In. Indium is separated from other constituents by sequential extractions of the bromide, cupferronate, and acetylacetonate, and is then reacted with a substoichiometric amont of EDTA. Excess of indium is removed by acetylacetone extraction and the specific activity of the complexed fraction is determined by counting ¹¹⁴In. Analyses of the U.S.G.S. standard rocks are reported. These show good agreement with previous neutron activation analyses. Repetitive rock analyses indicated an analytical precision of ±4–7%.