A flow injection on-line sorption preconcentration system has been synchronously coupled to an ETAAS system for the selective determination of (u1tra)trace amounts of Sb"' in water. The determination was achieved by selective complexation of Sb"' with ammonium pyrrolidine dithiocarbamate (APDC) at a wide range of sample acidity (0-1 mol 1-1 HCl), sorption of the complex onto the inner walls of a knotted reactor made from (100 cm long X 0.5 mm id) PTFE tubing, quantitative elution with 35 pl of ethanol and subsequent ETAAS detection. In order to minimize dispersion and to reduce the eluent volume required for the quantitative elution, an air flow was used to drive the eluent elution and to deliver all the eluate into an unpreheated polycrystalline graphite tube without a platform. Precise timing was not needed for analyte elution and eluate introduction. ETAAS determination of the analyte was performed in parallel with the preconcentration of the next sample. Using a preconcentration time of 30 s and a sample loading flow rate of 5.4 ml min-l, an enhancement factor of 30 was obtained in comparison with direct injection of 35 pl aqueous solution, resulting in a sampling frequency of 42 samples h-l. The detection limit (3s) was 0.021 pg 1-I and the precision was 2.9% (RSD) for eleven replicate determinations at 1 pg I-'. The introduction of an efficient wash step before elution with the addition of APDC to the wash medium permitted the use of simple aqueous standards for direct calibration in the analysis of sea-water. The accuracy of the proposed method was demonstrated by analysing synthetic mixtures and spiked sea-water.

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