ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF MOLYBDENUM IN WATER, HUMAN HAIR AND HIGH-PURITY REAGENTS WITH FLOW-INJECTION ONLINE COPRECIPITATION PRECONCENTRATION

A flow injection (FI) on-line coprecipitation preconcentration system has been developed for the electrothermal atomic absorption spectromet ric determination of trace or ultratrace amounts of molybdenum in wate r, human hair and high-purity sodium chloride. Molybdenum was coprecip itated with Fe-II-Pyrrolidin-1-yldithioformate (pyrrolidinedithiocarba mate) in 0.4 mol l(-1) HCl medium and collected on the walls of a knit ted reactor. After washing, the precipitate was dissolved with 50 mu l of isobutyl methyl ketone (IBMK) and the IBMK concentrate zone was di rectly introduced into the graphite tube from the FI system. Electroth ermal atomic absorption spectrometric determination of the concentrate d analyte was carried out in parallel with the next preconcentration c ycle. An enrichment factor of 22 was achieved with a 30 s loading time at a sample flow rate of 2.3 ml min(-1). The detection limit (3s) was 0.04 mu g l(-1) for a 30 s sample loading time and 0.02 mu g l(-1) fo r a 60 s loading time. A precision of 3.1% relative standard deviation was obtained at the 1.3 mu g l(-1) level. Recoveries of spiked molybd enum in tap water, sea-water and sodium chloride reagent mere in the r ange 94-104%. The result obtained for a human hair certified reference material was in good agreement with the certified value.