DETERMINATION OF SILVER IN WATERS AND SOIL BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY AFTER COMPLEXATION AND SORPTION ON CARBON

A method for the preconcentration of silver is proposed. Silver is complexed by the ammonium salt of dithiophosphoric acid O,O-diethyl ester and sorbed on to carbon. After desorption in a small volume of nitric acid solution, silver is determined by electrothermal atomic absorption spectrometry. In de-ionized water the yield was about 70%, indicating incomplete complexation and/or sorption on the carbon. In purified sea-water (sea-water submitted to solvent extraction to extract silver), the yield was less, about 40%, probably due to the effect of concomitants in the sea-water. The method was applied to sea and river waters and to a soil reference material. Spiked sea-water samples produced an average recovery of 102%, indicating good accuracy if analytical solutions in purified sea-water are used for the calibration. The detection limit (k = 3) for 200 ml of sea-water is 0.3 ng l-1. After acid dissolution of the soil sample, ascorbic acid should be added, prior to the complexing agent, to avoid interference of iron(III). Because of the small final volume, high enrichment factors can be obtained.