DETERMINATION OF ULTRA TRACES OF THALLIUM IN NATURAL-WATERS BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY AFTER SOLVENT-EXTRACTION ANDBACK-EXTRACTION

An effective method for the determination of thallium at ng/L levels i n natural waters is described. Thalluim is extracted with benzene as t he diethyldithiocarbamate complex and subsequently back-extracted into 0.2 mL of nitric acid. The back-extracted solution containing 50 mg/L of palladium as a matrix modifier is suitable for the determination o f thallium by graphite furnace atomic absorption spectrometry. As the extractivity of thallium (III) was poorer than thallium(I), total thal lium content was determined after reduction of thallium(III) with asco rbic acid. When 700 mL of sample was used, the detection limit(3 sigma ) was found to be 0.86 ng/L of thallium in the initial solution based on a 2800-fold preconcentration. The relative standard deviation was 3 .3% (20 ng/L, n = 8). The proposed method is simple and rapid for the determination of ultra-trace amounts of thallium in natural waters. Th e dissolved thallium content in river water was 6.49 ng/L, and those i n coastal sea waters were 13.4 and 15.3 ng/L.