A sensitive spectrophotometric method for determination of trace quantities of indium in soil

A simple and very sensitive method determining microgram quantities of indium in soil has been developed. The spectrophotometric method (epsilon = 1.74 x 10(5) l mol(-1) cm(-1)) based on the mixed complex In (III) with Chrome Azurol S and benzyldodecyldimethylammonium bromide was used for the analysis. A preliminary separation is made by extracting indium into butyl acetate from 5 M HBr solution. The selectivity of indium extraction and determination in the presence of macro- and micro components of soil was studied. Prior reduction of Fe (III) to Fe (II) with ascorbic acid prevents its co-extraction with indium. Indium was determined in synthetic mixtures corresponding to soil compositions and real samples of soil from different agricultural and industrial regions of Poland. The content of indium was found from the calibration graph (in the range, 0.12-0.48 mu g/ml; r = 0.9991) obtained after extraction. The precision was satisfactory: % RSD (n = 6) ranged from 2.7 to 8.2. The average indium standard recovery ranged from 95 to 101%. Analysis using an ICP-OES method gave comparable results.