FLAME ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF LEAD IN BIOLOGICAL SAMPLES USING A FLOW-INJECTION SYSTEM WITH ONLINE PRECONCENTRATION BY COPRECIPITATION WITHOUT FILTRATION

A procedure for the coprecipitation of lead in the presence of high concentrations of iron, originally described as a batch process, was modified and adapted to on-line preconcentration using a flow injection system for flame atomic absorption spectrometry. Lead was coprecipitated quantitatively with the iron(II)-hexahydroazepinium hexahydroazepin-1-ylformate (hexamethyleneammonium hexamethylenedithiocarbamate) complex and collected in a knotted reactor made of Microline tubing (150 cm x 0.5 mm i.d.) without using a filter. The precipitate was dissolved in isobutyl methyl ketone and introduced directly into the nebulizer-burner system of an atomic absorption spectrometer. An enrichment factor of 20 and an enhancement factor of 66 were obtained for a coprecipitation time of 30 s, resulting in a sampling frequency of 90 h-1. A detection limit (3-sigma) of 2-mu-g l-1 in the sample solution was obtained and the precision at the 200-mu-g l-1 level was 2.7% relative standard deviation (n = 12). Up to 250 mg l-1 of iron in the sample solution could be tolerated without causing any significant decrease in the lead signal. The results obtained for the determination of lead in reference materials (blood and bovine liver) demonstrate the applicability of the procedure to the analysis of biological materials.