Ultratrace determination of cobalt in natural waters by electrothermal atomic absorption spectrometry using flow-injection on-line sorption preconcentration in a knotted reactor precoated with 1-phenyl-3-methyl-benzoylpyrazol-5-one

A fully automated procedure was developed for the ultratrace determination of cobalt in natural waters by on-line flow injection (FI) sorption preconc entration of metal chelate complexes on the walls of a PTFE knotted reactor precoated with a chelating reagent, coupled with electrothermal atomic abs orption 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 reag ents for this system. PMBP offered the best performance characteristics for the preconcentration of Co. An enhancement factor of 28 and a detection li mit (3 sigma) 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 mu g l(-1) Co. The interference caused by Al(III) was overcome by the us e of fluoride as a masking agent while the interferences from Cu, Fe(II) an d Fe(III) were masked by thiourea. The accuracy of the method was demonstra ted by the analysis of certified reference materials and recovery measureme nts on spiked samples.