Application of Solid-Phase Extraction in Metal Speciation

Abstract

Solid-phase extraction materials that consist of C 18 and amino (LC-NH 2) functionalities are used to extract metal species in aqueous solutions. The C 18 is employed after the metal species are converted into a neutral complex with dithizone. The complex is then eluted from the C 18 substrate by using an eluent that consists of acetonitrile in nitric acid medium. Although the C 18 material is found to be suitable for the extraction of neutral metal complexes, the LC-NH 2 material is applicable to the direct extraction of free metal species. Moreover, because the NH 2 functionality is amenable to protonation, sample acidity has a significant influence on the nature and effectiveness of the extraction process. In general, solidphase extraction immobilizes metal species on the solid substrate, thereby maintaining its stability. This is found to be particularly true for the neutral metal complexes extracted on the C 18 material. Dithizone metal complexes are generally quite unstable under normal atmospheric conditions. When the complex is extracted and left on the solid substrate, however, its stability is unchanged. Closely related to species stability is sample matrix, the effects of which are completely eliminated by immobilizing the analyte on the solid substrate. The separation of the analyte from the sample matrix also facilitates its preconcentration. Measurement sensitivity is increased several factors by the extraction of several aliquots of dilute solutions of the analyte.