FLOW-INJECTION ONLINE SORPTION PRECONCENTRATION IN A KNOTTED REACTOR FOR ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF ULTRATRACE AMOUNTS OF COBALT IN NATURAL-WATERS

A pow-injection on-line sorption preconcentration-electrothermal atomi c absorption spectrometric (ETAAS) method has been developed for the d etermination of ultratrace amounts of cobalt in natural waters. The pr econcentration wets achieved by online complexation of cobalt with amm onium pyrrolidine dithiocarbamate and subsequent sorption of the compl ex onto the inner walls of a knotted reactor, made of a 0.5 mm i.d. an d 100 cm long PTFE tubing. In order to reduce the eluate volume and to minimize dispersion, an air flow was used to drive the eluent for the elution of the adsorbed analyte and to dispel the eluate into the gra phite tube. The adsorbed analyte complex was quantitatively eluted wit h 45 mu L of ethanol, and all the ethanolic eluate was successfully in troduced at a relatively high flow rate (2.7 mL min(-1)) into an uncoa ted polycrystalline graphite tube without need of a platform nor a pre heating step. ETAAS determination was performed in parallel with the p reconcentration of the next sample. With a sample consumption of 6.7 m L, an enhancement factor of 47 in comparison with direct injection of 45 mu L aqueous solution was obtained at a sampling frequency of 31 h( -1). The detection limit (3 sigma) was found to be 2.8 ng L-1. The pre cision was 3% relative standard deviation (RSD) at the 0.2 mu g L-1 le vel (n = 11). The results obtained by the proposed method for a number of water standard reference materials are in good agreement with the certified values. (C) 1997 John Wiley & Sons, Inc.