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

Abstract

An all-silica interface for coupling flowing liquid streams with on-line monitoring by atomic absorption spectrometry (AAS), was evaluated for the determination of Cd, Cu, Pb, Zn and Hg. In operation, the mobile phase was nebulized by thermospray effect into a hydrogen–oxygen diffused flame maintained within a heated pyrolysis chamber. The expanding gases entrained the combustion products into an optical tube mounted within the optical beam of the spectrometer. Low to sub-nanogram limits of detection for each of the elements were achieved with either an aqueous or a methanolic mobile phase. Although optimal operating conditions of the interface were somewhat different for each analyte element, the optimum total flow of make-up gases and the ratio of H₂:O₂, as predicted by response surface models, were surprisingly similar for Cd, Cu, Pb and Zn detection. Yet the ratio of O₂:H₂ flow to the interface was important only for the determination of Pb. By contrast to the other metals, determination of Hg was optimized by turning off the flows of these gases to the interface. The response to Hg was increased 6-fold by substituting methanol for water as the mobile phase carrier. By contrast, the AAS responses to the other elements was unaffected by this change in carrier solvent. The utility of the high-performance liquid chromatography (HPLC)–AAS interface was demonstrated by monitoring the Cd, Zn or Cu bound to a crude metallothionein isolate from a single freshwater mollusc by gel permeation HPLC.