Determination of trace elements in sea-water by inductively coupled plasma mass spectrometry after preconcentration by formation of water-soluble complexes and their adsorption onC18-bonded silica gel

Abstract

A simple and reliable preconcentration method was developed for the determination of seven trace metals (Mn, Fe, Ni, Cu, Zn, Cd and Pb) in sea-water by ICP-MS. The method is based on the formation of water-soluble complexes in an aqueous sample followed by adsorption of the complexes onto a C₁₈-bonded silica gel column. The chelating reagent used was 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS). By passage of 100 ml of sea-water sample, after addition of 5-Br-PAPS and adjustment of the pH to 8.3, quantitative adsorption of the metal complexes onto the column took place while the major matrix ions in sea-water passed through the column. A similar but separate sample work-up at pH 4.5 provided acceptably low blank values for Fe. The metals were subsequently eluted with 4.0 ml of 1.0 M HNO₃. All seven elements were determined with an all-argon plasma, whereas ultratrace levels of Fe were determined with a nitrogen–argon mixed-gas plasma to reduce the isobaric interference by ⁴⁰Ar¹⁶O on ⁵⁶Fe. The detection limits of the method, based on a 25-fold preconcentration, range from 0.08 ng l^–1 for Cd to 16 ng l^–1 for Fe. The precision and accuracy of the method were demonstrated by analyzing coastal and open-ocean sea-water certified reference materials.