SPECTROPHOTOMETRIC DETERMINATION OF GALLIUM(III) WITH CARMINIC ACID AND HEXADECYLPYRIDINIUM CHLORIDE

The coloured complex formed between Ga(III) and carminic acid (CA) was utilized for developing a spectrophotometric method of gallium determ ination 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 wa s 1.4 in the presence of HDPC. The complex exhibited a molar absorptiv ity of 3.0 x 10(4) dm(3) mol(-1) cm(-1) at 570 nm in an aqeous solutio n 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, thioglyco llic acid or fluoride. The developed method was successfully applied w ithout 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(I II) and Al(III).