Determination of gallium and indium with haematoxylin in a micellar medium
The reactions of gallium and indium with haematoxylin (I) and its oxidised form (II) in the presence of cationic, anionic and non-ionic surfactants were investigated spectrophotometrically. Maximum enhancement of the absorbance of the complexes is obtained with the cationic surfactant cetyltrimethylammonium bromide (CTAB). The ternary complexes formed with I have a maximum absorbance at 610 nm with molar absorptivities of 1.37 × 105(Ga) and 1.33 × 105(ln) l mol–1 cm–1, the sensitivities being 0.0005 µg cm–2 of Ga and 0.0009 µg cm–2 of ln. The corresponding molar absorptivities of the ternary complexes with II are 9.5 × 104 and 1.1 × 105 l mol–1 cm–1 and the sensitivities are 0.0007 and 0.001 µg cm–2. Beer's law is obeyed up to 0.64 µg ml–1 of Ga and 1.0 µg ml–1 of ln with both reagents. The effects of reagent and CTAB concentrations, pH, standing time and interfering ions and the stoicheiometry of the complexes are discussed. The method was applied to the determination of trace amounts of gallium in aluminium metal and an aluminium-silicon alloy and to the determination of indium in a synthetic mixture containing 99% of gallium.