Determination of ultratrace metals of group-13 elements in natural water by graphite-furnace AAS after preconcentration with solvent extraction and back extraction

The need for highly sensitive and reliable methods for the determination of ultratrace elements has been recognized in analytical chemistry and/or environmental science. The author has developed micro-volume back-extraction methods for the ultratrace analysis of gallium, indium and thallium. At first the determination of gallium and indium at ng dm(-3) levels in natural water samples was investigated. Gallium or indium was extracted into carbon tetrachloride as an ion pair of 5-sulfo-8-quinolinol chelate anion with tetradecyldimethylbenzyl-ammonium chloride, and subsequently back-extracted into 0.3 cm(3) of nitric acid solution for determination by GFAAS. In the case of indium, the extraction behavior of the ion associate was compared with that of the 8-quinolinolato complex. Secondly, the determination of thallium at ng dm(-3) levels in natural water samples was investigated. Thallium is extracted into chloroform as the dithizonate complex, and subsequently back-extracted into 0.3 cm(3) of a nitric acid solution. A speciation analysis of Tl(I) and Tl(III) is performed by the masking of Tl(III) with citrate and/or the reduction of Tl(III) to Tl(I) with ascorbic acid. The detection limits obtained for these elements are sub ng dm(-3) levels, based on more than 1000-fold preconcentration.