FLAME ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF CADMIUM AND COPPER IN BIOLOGICAL REFERENCE MATERIALS USING ONLINE SORBENT EXTRACTION PRECONCENTRATION

Cadmium and copper at the mug/g to ng/g level in plant and animal tissue reference materials, and at the mug/l level in urine were determined by flame atomic absorption spectrometry using on-line sorbent extraction preconcentration based on flow injection techniques. Bonded silica reversed phase sorbent with octadecyl functional groups (RP-C 18), packed in a 100 mul column, was used to collect the diethylammonium-N,N-diethyldithiocarbamate (DDTC) complex formed on-line in the sample digests at low pH. Methanol was used to elute the analyte chelates directly into the nebulizer-burner system of the spectrometer. Small air segments introduced before and after elution prevented the eluent from mixing with the sample solution and increased the sensitivity. A sampling frequency of 85/h could be obtained with a sample loading time of 30 s at a flow rate of 4.0 ml/min. The enrichment factor for both elements was 20 and the enhancement factors, including the effect of the organic solvent and with the flow spoiler removed, were 126 and 114 for cadmium and copper, respectively. The detection limits (3sigma) were 0.15 mug/l for cadmium and 0.2 mug/l for copper. The precision was 2.3% and 1.4% r.s.d. for 10 mug/l Cd and 45 mug/l Cu, respectively (n = 11). Results for the determination of cadmium and copper in various biological reference materials were typically in good agreement with certified values. Low recoveries were observed, however, for cadmium in samples containing high levels of copper and/or iron, such as bovine liver.