DETERMINATION OF (ULTRA)TRACE AMOUNTS OF ANTIMONY(III) IN WATER BY FLOW-INJECTION ONLINE SORPTION PRECONCENTRATION IN A KNOTTED REACTOR COUPLED WITH ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

A flow injection on-line sorption preconcentration system has been syn chronously coupled to an ETAAS system for the selective determination of (ultra)trace amounts of Sb-III in water, The determination was achi eved by selective complexation of Sb-III with ammonium pyrrolidine dit hiocarbamate (APDC) at a wide range of sample acidity (0-1 mol l(-1) H Cl), 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 mu l of ethanol and subsequent ETAAS detection. In order to m inimize dispersion and to reduce the eluent volume required for the qu antitative elution, an air flow was used to drive the eluent elution a nd to deliver all the eluate into an unpreheated polycrystalline graph ite tube without a platform, Precise timing was not needed for analyte elution and eluate introduction, ETAAS determination of the analyte w as 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(-1), an enhancement factor of 30 was obtained in compari son with direct injection of 35 mu l aqueous solution, resulting in a sampling frequency of 42 samples h(-1). The detection limit (3s) was 0 .021 mu g l(-1) and the precision was 2.9% (RSD) for eleven replicate determinations at 1 mu g l(-1). The introduction of an efficient wash step before elution with the addition of APDC to the wash medium permi tted the use of simple aqueous standards for direct calibration in the analysis of sea-water. The accuracy of the proposed method was demons trated by analysing synthetic mixtures and spiked sea-water.