Determination of trace gallium in iron ores by 8-quinolinol-chloroform extraction/graphite furnace AAS

Trace quantities of Ga in ores were determined by graphite furnace AAS after solvent extraction. The analytical procedure is as follows; 0.5 g are is fused with 2 g sodium dioxide. After aqueous leaching, hydrochloric acid is added to make the solution acidic. Twenty mililiters of perchloric acid is added and the solution is heated until the appearance of fumes. Twenty mililiters of 10% ascorbic acid is added in order to reduce Fe (III) and Ti(IV) {in the case of a Ti(IV) oxide content higher than 5%, 25 ml of 20% ascorbic acid is used}. The pH of the solution is adjusted to 2.5±0.1 with 20% ammonium acetate. Gallium is extracted with 40 ml of 0.01 M 8-quinolinol in chloroform and re-extracted from the organic phase with 30 ml of 1.5 M nitric acid. The water phase is gently heated in order to expel the chloroform dissolved. Five mililiters of nickel nitrate solution (50 mgNi/ml) is added for matrix modification. The solution is transferred to a 50 ml volumetric flask. An aliquot of 20μl is injected on a graphite furnace equipped with a platform and the absorbance of Ga is measured at 417.2 nm. The analytical precision was obtained by repetitive determination of Ga in JSS 800-2 (Rompin Hematite). The averaged analytical value was 0.0012o% and the relative standard deviation was 1.62%. The limit of detection(3σ) is 0.13 ppm for 0.5 g sample taken. The pyrolytically coated graphite furnace equipped with a platform made it possible to determine the analyte more precisely and ca.300 repetitive firing with one graphite furnace became also possible.