Spectrophotometric determination of gallium(III) with carminic acid and hexadecylpyridinium chloride

Abstract

The coloured complex formed between Ga(III) and carminic acid (CA) was utilized for developing a spectrophotometric method of gallium determination in the presence of the cationic surfactant hexadecylpyridinium chloride (HDPC), which caused a bathochromic shift in the absorption spectrum and an increase in extinction. The Ga(III): CA molar ratio was 1.4 in the presence of HDPC. The complex exhibited a molar absorptivity of 3.0 x 10(4) dm(3) mol(-1) cm(-1) at 570 nm in an aqeous solution of pH 4.0. Beer's law was obeyed between 2.0 x 10(-6)-2.0 x 10(-5) M Ga(III), and the relative standard deviation for gallium analysis was 1.4%. Most ions did not interfere, with a few exceptions which could be masked with either diethyldithiocarbamate, ascorbic acid, thioglycollic acid or fluoride. The developed method was successfully applied without any preliminary separation to gallium determination in gallium arsenide (GaAs) semiconductor materials, and with prior extraction in a geostandard tonalite sample containing very high proportions of Fe(III) and Al(III).