DETERMINATION OF CADMIUM, LEAD AND COPPER IN WATER SAMPLES BY FLAME ATOMIC-ABSORPTION SPECTROMETRY WITH PRECONCENTRATION BY FLOW-INJECTION ONLINE SORBENT EXTRACTION

Cadmium, lead and copper were determined in synthetic sea-water, drinking water and the NBS 1643b Trace Elements in Water standard reference material at mu-g/l. levels by flame atomic-absorption spectrometry after on-line preconcentration by sorbent extraction with a flow-injection system. Bonded silica with octadecyl functional groups packed in a micro column of 100-mu-l capacity was used to collect diethylammonium diethyldithiocarbamate complexes of the heavy metals in the aqueous samples. The sample loading time was 20 sec at a flow-rate of 3.3 ml/min. Ethanol or methanol was used to elute the adsorbed analytes into the spectrometer. The sample loading rate, elution rate and pH were optimized. Enrichment factors of 19-25 for Cd, Pb and Cu were achieved at sampling frequencies of 120/hr with precisions of 1.4 1.0 and 1.3% rsd (n = 11), respectively. The detection limits (3-sigma) for Cd, Pb and Cu were 0.3, 3 and 0.2-mu-g/l., respectively. Determination of Cd, Pb and Cu in NBS SRM 1643b showed good agreement with the certified values. Recoveries of Cd and Pb added to sea-water were 95 and 102%, respectively.