Flow-injection on-line sorption preconcentration in a knotted reactor for electrothermal atomic absorption spectrometric determination of ultratrace amounts of cobalt in natural waters

Abstract

A flow-injection on-line sorption preconcentration–electrothermal atomic absorption spectrometric (ETAAS) method has been developed for the determination of ultratrace amounts of cobalt in natural waters. The preconcentration was achieved by on-line complexation of cobalt with ammonium pyrrolidine dithiocarbamate and subsequent sorption of the complex onto the inner walls of a knotted reactor, made of a 0.5 mm i.d. and 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 graphite tube. The adsorbed analyte complex was quantitatively eluted with 45 μL of ethanol, and all the ethanolic eluate was successfully introduced at a relatively high flow rate (2.7 mL min−1) into an uncoated polycrystalline graphite tube without need of a platform nor a preheating step. ETAAS determination was performed in parallel with the preconcentration of the next sample. With a sample consumption of 6.7 mL, an enhancement factor of 47 in comparison with direct injection of 45 μL aqueous solution was obtained at a sampling frequency of 31 h−1. The detection limit (3 σ) was found to be 2.8 ng L−1. The precision was 3% relative standard deviation (RSD) at the 0.2 μg L−1 level (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. © 1997 John Wiley & Sons, Inc. Lab Robotics and Automation 9: 191–199, 1997.