Electrothermal atomic absorption spectrometric determination of cobalt in biological samples and natural waters using a flow injection system with on-line preconcentration by ion-pair adsorption in a knotted reactor

An on-line flow injection preconcentration-ETAAS method is developed for tr ace determination of cobalt in biological materials and natural samples by ion-pair sorption on the inner walls of a PTFE knotted reactor. The ion-pai r is formed between the negatively charged cobalt-nitroso-R-salt complex an d the tetrabutylammonium counter-ion. An enhancement factor of 15, a sampli ng frequency of 17 and a concentration efficiency of 4 are obtained for a p reconcentration time of 60 s and a sample loading flow rate of 5 mL min(-1) . The detection limit (3 sigma) is 5 ng L-1. The relative standard deviatio n at the 0.2 mu g L-1 level is 2.3%. The analytical results obtained for st andard reference materials are in good agreement with the certified or indi cated values and satisfactory recoveries of spiked cobalt in tap water are obtained.