1979 Volume 28 Issue 6 Pages 385-388
A method is described for the spectrophotometric determination of gallium(III), which is based on the extraction of gallium(III)-2-bromo-4, 5-dihydroxyazo-benzene-4'-sulfonate (BDAS) complex into 1-butanol in the presence of 1, 3-diphenylguanidinium(DPG) salt. The extraction species has an absorption maximum at about 495 nm, and a constant absorbance is obtained in the pH range 5.7 to 6.2. The procedure is as follows: To a sample solution containing up to 11μg of gallium(III) in a 50 ml separatory funnel were added 3 ml of a 1.0 ×10-3 M BDAS solution and 5 ml of 0.17 M DPG solution which had been adjusted to pH 5.9 with hydrochloric acid and hexamethylene-tetramine solutions. The solution was diluted with water to 20.0 ml and shaken for 5 min with 10.0 ml of 1-butanol. The absorbance of the organic phase was then measured at 495 nm using the reagent blank as a reference. Under the optimum condition, a linear relationship between the absorbance of the organic phase and the gallium(III) content of the aqueous phase is obtained up to 11μg gallium(III) per 20.0 ml. The molar absorptivity of the extracted species is 5.5 ×104 cm-1 mol-1 1 at 495 nm. Iron(III), indium(III), aluminum(III), titanium(IV), zirconium (IV), tungsten(VI), and molybdenum(VI) interfered with the determination of gallium (III) even when present in equimolar amounts that of gallium(III). The interferences from aluminum and thorium (IV) can be eliminated by the addition of sodium fluoride. The composition of the extracted species is gallium (III) : BDAS : DPG = 1 :2 : 2.
