Diffuse reflection spectroscopy of indium sorbates with immobilized heterocyclic azo compounds

Diffuse reflection has been used for the direct determination of indium after preconcentration on a solid support. The best conditions were found for sorption of indium complexes with 1-(2-pyridylazo)-2-naphthol (PAN), 4-(2-pyridylazo)resorcinol (PAR) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) immobilized on a silica gel Silochrom S-120. Optical characteristics of the complexes in solutions and on sorbent are practically the same for the variations of the Gurevich–Kubelka–Munk function, color lightness and chromaticity coordinates. The linear solutions of variations of these quantities with the indium contents were determined. It was demonstrated that 4 μg indium could be concentrated on 0.3 g modified silica gel with immobilized 5-Br-PADAP from a sample volume of 200 ml with an enrichment factor exceeding 600.