INVESTIGATION OF ONLINE COUPLING ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY WITH FLOW-INJECTION SORPTION PRECONCENTRATION USING A KNOTTED REACTOR FOR TOTALLY AUTOMATIC-DETERMINATION OF LEAD IN WATER SAMPLES

A flow injection on-line sorption preconcentration electrothermal atom ic absorption spectrometric system for fully automatic determination o f lead in water was investigated. The discrete non-how-through nature of ETAAS, the limited capacity of the graphite tube and the relatively large volume of the knotted reactor (KR) are obstacles to overcome fo r the on-line coupling of the KR sorption preconcentration system with ETAAS. A new FI manifold has been developed with the aim of reducing the eluate volume and minimizing dispersion. The lead diethyldithiocar bamate complex was adsorbed on the inner walls of a knotted reactor ma de of PTFE tubing (100 cm long, 0.5 mm i.d.). After that, an air flow was introduced to remove the residual solution from the KR and the elu ate delivery tube, then the adsorbed analyte chelate was quantitativel y eluted into a delivery tube with 50 mu l of ethanol. An air how was used to propel the eluent from the eluent loop through the reactor and to introduce all the ethanolic eluate onto the platform of the transv ersely heated graphite tube atomizer, which was preheated to 80 degree s C. With the use of the new FI manifold, the consumption of eluent wa s greatly reduced and dispersion was minimized. The adsorption efficie ncy was 58%, and the enhancement factor was 142 in the concentration r ange 0.01-0.05 mu g l(-1) Pb at a sample loading rate of 6.8 ml min(-1 ) with 60 s preconcentration time. For the range 0.1-2.0 mu g l(-1) of Pb a loading rate of 3.0 ml min(-1) and 30 s preconcentration time we re chosen, resulting in an adsorption efficiency of 42% and an enhance ment factor of 21, respectively. A detection limit (3 sigma) of 2.2 ng l(-1) of lead was obtained using a sample loading rate of 6.8 ml min( -1) and 60 s preconcentration. The relative standard deviation of the entire procedure was 4.9% at the 0.01 mu g l(-1) Pb level with a loadi ng rate of 6.8 ml min(-1) and 60 s preconcentration, and 2.9% at the 0 .5 mu g l(-1) Pb level with a 3.0 ml min(-1) loading rate and 30 s pre concentration. Efficient washing of the matrix from the reactor was cr itical, requiring the use of the standard addition method for seawater samples. The analytical results obtained for seawater and river water standard reference materials were in good agreement with the certifie d values.