PERFORMANCE OF A SILICA T-TUBE INTERFACE FOR THE DETERMINATION OF CADMIUM, COPPER, LEAD, ZINC AND MERCURY IN FLOWING LIQUID STREAMS BY ATOMIC-ABSORPTION SPECTROMETRY

An all-silica interface for coupling flowing liquid streams with on-li ne monitoring by atomic absorption spectrometry (AAS), was evaluated f or the determination of Cd, Cu, Pb, Zn and Hg. In operation, the mobil e phase was nebulized by thermospray effect into a hydrogen-oxygen dif fused flame maintained within a heated pyrolysis chamber. The expandin g gases entrained the combustion products into an optical tube mounted within the optical beam of the spectrometer. Low to sub-nanogram limi ts of detection for each of the elements were achieved with either an aqueous or a methanolic mobile phase. Although optimal operating condi tions of the interface were somewhat different for each analyte elemen t, the optimum total flow of make-up gases and the ratio of H-2:O-2, a s predicted by response surface models, were surprisingly similar for Cd, Cu, Pb and Zn detection. Yet the ratio of O-2:H-2 flow to the inte rface was important only for the determination of Pb. By contrast to t he other metals, determination of Hg was optimized by turning off the flows of these gases to the interface. The response to Hg was increase d 6-fold by substituting methanol for water as the mobile phase carrie r. By contrast, the AAS responses to the other elements was unaffected by this change in carrier solvent. The utility of the high-performanc e liquid chromatography (HPLC)-AAS interface was demonstrated by monit oring the Cd, Zn or Cu bound to a crude metallothionein isolate from a single freshwater mollusc by gel permeation HPLC.