Determination of indium(III) with 3,4,5,6-tetrachlorogallein and cetylpyridinium chloride

Rapid and highly sensitive methods have been developed for the spectrophotometric and titrimetric determination of indium(III) with 3,4,5,6-tetrachlorogallein(3,4,5,6-T. Cl, Gal.) and cetylpyridinium chloride(CPC) in aqueous solutions of pH 4.2--5.2. The absorbance of the indium(III)-3,4,5,6-T. Cl. Gal. complex at 620 nm and the color change (pure blue - weak violetish red) were used to indicate the end point in the EDTA titration. The calibration curve for the spectrophotometry was linear in the range 0--45.0 μg In(III)/10 ml. According to Sandell's expression, the sensitivity was 0.0032 μg In(III)/cm2 for an absorbance of 0.001. To the solution containing less than 45.0 μg of indium(III), 2.0 ml of 1.0x10-2M CPC solution, 3.0 ml of Walpole buffer solution(pH 4.4; acetic acid-sodium acetate), and 2.0 ml of 1.0x10-3M 3,4,5,6-T.Cl.Gal. methanol solution were added and the volume was made up to 10.0 ml with water. The solution was kept at (20--25)0C for 30 minutes and then the absorbance was measured at 620 nm against the reagent blank. The mole ratio of indium(III), 3,4,5,6-T.Cl.Gal. and CPC in the complex was estimated to be 1 : 2 : 2 by the continuous variation and the mole ratio methods. (auth.)