FLAME ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF CADMIUM, COBALT, AND NICKEL IN BIOLOGICAL SAMPLES USING A FLOW-INJECTION SYSTEM WITH ONLINE PRECONCENTRATION BY COPRECIPITATION WITHOUT FILTRATION

Cadmium, cobalt, and nickel at ng/g to mu-g/g levels in plant and animal tissue reference materials and at mu-g/L levels in blood and urine were determined by flame atomic absorption spectrometry. The analyte elements were preconcentrated and separated from the bulk of the matrix by on-line co-precipitation with the hexamethylene ammonium hexa-methylene dithiocarbamate iron(II) chelate complex in a flow injection system. The precipitate was collected in a knotted reactor made from 150-cm-long, 0.5-mm-i.d. Microline tubing without using a filter. The precipitate was dissolved in methyl isobutyl ketone and introduced directly into the nebulizer-burner system of an atomic absorption spectrometer. Ascorbic acid in an HC1/KC1 buffer was added on-line in order to reduce iron(III) to iron(II) because of its much better efficiency as a collector for trace elements. Reagent concentrations were optimized so that at least 200 mg/L of iron and 15 mg/L of copper could be tolerated in the sample solution without causing significant interferences. The portion of the analyte retained in the collector was about 70% for cadmium and 50% for cobalt and nickel. Enrichment factors of 24, 19, and 20 were obtained for cadmium, cobalt, and nickel, respectively, with the use of a 40-s co-precipitation time, resulting in enhancement factors, including the effect of the organic solvent, of 52, 43, and 52, respectively. The detection limits (3-sigma) for cadmium, cobalt and nickel were 0.15, 1.3, and 1.5-mu-g/L, respectively, and the precision was 1.5% RSD for 10-mu-g/L Cd, 2.7% RSD for 50-mu-g/L Co, and 1.8% RSD for 50-mu-g/L Ni. The analytical results obtained for a number of standard reference materials and control samples were in good agreement with the certified or recommended values.