DETERMINATION OF ULTRATRACE GALLIUM IN RIVER WATER BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY AFTER PRECONCENTRATION WITH SOLVENT-EXTRACTION AND BACK-EXTRACTION

A method for the determination of gallium at ng dm(-3) levels in river water is described. Gallium is extracted into carbon tetrachloride as an ion pair of gallium-5-sulfo-8-quinolinol (H(2)QS) chelate anion wi th tetradecyldimethylbenzylammonium chloride (Zephiramine), and subseq uently back-extracted into 0.3 cm(3) of a nitric acid solution. The hi gh efficiency of extraction and back extraction allows gallium to be c oncentrated about 5000-fold with a combined single extraction and back extraction. The back-extracted solution, containing 250 mu g cm(-3) o f nickel as a matrix modifier, is suitable for the determination of ga llium by electrothermal atomic absorption spectrometry (ETAAS). The de tection limit (3 sigma) for gallium is 0.29 ng dm(-3) based on a 1500- fold preconcentration. The concentration of dissolved gallium in river water was found to be 5.3-9.2 ng dm(-3) by the proposed method.