RESUMO
A new, sensitive and robust time-based flow injection (FI) method for on-line preconcentration and determination of ultra trace amounts of chromium(VI) by flame atomic absorption spectrometry (FAAS) has been elaborated. The sample is initially mixed on-line with ammonium pyrrolidine dithiocarbamate (APDC) and the Cr(VI)-PDC chelate is absorbed quantitatively on a mini-column packed with polytetrafluoroethylene (PTFE) turnings at a pH range 0.8-1.4. The complex is subsequently eluted with isobutyl methyl ketone (IBMK) and introduced directly into the nebulizer-burner system. The optimized system offered improved performance characteristics, with unlimited lifetime of the proposed column. The enhancement factor was 80, for a 3-min preconcentration time and the sample frequency was 18 h(-1). The calibration curve was linear over the concentration range 1-40 mug l(-1) with a detection limit of c(L)=0.8 mug l(-1) and a relative standard deviation of s(r)=3.2%, at the 20 mug l(-1) level. The proposed method was evaluated by analyzing samples of certified and spiked water, and it was applied to the analysis of natural water samples and sediments.
