Flame atomic absorption spectrometric determination of chromium(VI) by on-line preconcentration system using a PTFE packed column

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 μg l−1 with a detection limit of cL=0.8 μg l−1 and a relative standard deviation of sr=3.2%, at the 20 μg 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.