Spectrophotometric and titrimetric determination of gallium in minerals and ores using semimethylthymol blue

The composition, overall stability constant and molar absorptivity of the chelate of gallium(III) ion with semimethylthymol blue, SMTB, were determined spectrophotometrically in acetate buffer (pH 4.5-5). A violet Ga(SMTB) chelate was formed with logarithmic overall stability constant of 18.0 +/- 0.1 (I = 0.1) and molar absorptivity of 4.25 x 10(4) l mol(-1) cm(-1) (lambda(max) 580 nm). SMTB is proposed as a new reagent for the spectrophotometric determination of micro-molar amounts of gallium(III). The colour development depends on time, temperature, pH and buffer species. The interference of different cations, anions and organic acids on gallium(III) determination was also investigated. Beer's law was obeyed for 3.5-31.3 mu gGa(III)/25 ml (0.14-1.25 mu g ml(-1)). SMTB was used for the spectrophotometric determination of gallium in different grade minerals and ores and the results were of acceptable error and relative standard deviation. Comparison between the two suggested methods and atomic absorption spectrometry for Ga(III) determination was carried out.