ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF LEAD IN HIGH-PURITY REAGENTS WITH FLOW-INJECTION ONLINE MICROCOLUMN PRECONCENTRATION AND SEPARATION USING A MACROCYCLE IMMOBILIZED SILICA-GEL SORBENT

A fully automated procedure for the determination of ng l(-1) amounts of lead has been developed using flow injection (FI) online column pre concentration coupled with electrothermal atomic absorption spectromet ry (ETAAS). The proposed FI manifold and its operation make possible t he introduction of the total eluate volume into the graphite atomizer, avoiding the necessity for optimization of subsampling the eluate. Th e interference of other heavy metal ions due to competition for active sites of the sorbent is overcome using a highly selective macrocycle immobilized on silica gel (Pb-02). Lead is adsorbed on a microcolumn ( 50 mu l) packed with Pb-02, and after washing the column with dilute n itric acid, air is introduced to remove all solution from the column a nd connecting tubing. The sorbed analyte is then eluted quantitatively into the graphite tube atomizer, preheated to 100 degrees C, with 36 mu l of ETDA solution (0.035 mol l(-1), pH 10.5), propelled by air in order to minimize dispersion. The collection efficiency was 77% and wi th a sample loading flow rate of 3 ml min(-1) and a 60 s preconcentrat ion time, the enhancement factor was 77 and the throughput was 17 samp les per hour. The relative standard deviation (n = 10) at the 300 ng l (-1) level was 2.7%, and the detection limit (3 sigma) was 0.4 ng l(-1 ). No interference from heavy metals was observed, but ions of Ba2+, S r2+ and K+ were found to interfere when the concentration ratios of in terferent to lead exceeded values of 2000, 20 000 and 200 000, respect ively. Quantitative recovery of lead was achieved from sodium, magnesi um, aluminum, lanthanum and heavy metal salt solutions. The high selec tivity and sensitivity, combined with extremely low blank values, make the proposed technique particularly attractive for the analysis of hi gh-purity reagents, semiconductors and other high-purity materials. Re sults are presented for the determination of lead in some high-purity reagents.