Electrothermal atomic absorption spectrometric determination of molybdenum in water, human hair and high-purity reagents with flow injection on-line coprecipitation preconcentration

Abstract

A flow injection (FI) on-line coprecipitation preconcentration system has been developed for the electrothermal atomic absorption spectrometric determination of trace or ultratrace amounts of molybdenum in water, human hair and high-purity sodium chloride. Molybdenum was coprecipitated with Fe^II–pyrrolidin-1-yldithioformate (pyrrolidinedithiocarbamate) in 0.4 mol l^–1 HCl medium and collected on the walls of a knitted reactor. After washing, the precipitate was dissolved with 50 µl of isobutyl methyl ketone (IBMK) and the IBMK concentrate zone was directly introduced into the graphite tube from the FI system. Electrothermal atomic absorption spectrometric determination of the concentrated analyte was carried out in parallel with the next preconcentration cycle. 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 µg l^–1 for a 30 s sample loading time and 0.02 µg l^–1 for a 60 s loading time. A precision of 3.1% relative standard deviation was obtained at the 1.3 µg l^–1 level. Recoveries of spiked molybdenum in tap water, sea-water and sodium chloride reagent were in the range 94–104%. The result obtained for a human hair certified reference material was in good agreement with the certified value.