Abstract

A fully automated procedure was developed for the ultratrace determination of cobalt in natural waters by on-line flow injection (FI) sorption preconcentration of metal chelate complexes on the walls of a PTFE knotted reactor precoated with a chelating reagent, coupled with electrothermal atomic absorption spectrometry (ETAAS). Ammonium pyrrolidinedithiocarbamate (APDC), 8-hydroxyquinoline (HQ), 1-phenyl-3-methyl-4-benzoylpyrazol-5-one (PMBP) and 2-nitroso-1-naphthol-4-sulfonic acid (NNA) were compared as chelating reagents for this system. PMBP offered the best performance characteristics for the preconcentration of Co. An enhancement factor of 28 and a detection limit (3σ) of 8.1 ng l⁻¹ are achieved with 120 s preconcentration time at a sample flow rate of 1.2 ml min⁻¹. The precision (RSD) is 2.1% for 0.2 µg l⁻¹ Co. The interference caused by Al(III) was overcome by the use of fluoride as a masking agent while the interferences from Cu, Fe(II) and Fe(III) were masked by thiourea. The accuracy of the method was demonstrated by the analysis of certified reference materials and recovery measurements on spiked samples.