Determination of trace elements in sea-water by inductively coupled plasma mass spectrometry after preconcentration by formation of water-soluble complexes and their adsorption on C18-bonded silica gel

A simple and reliable preconcentration method was developed for the determination of seven trace metals (Mn, Fe, Wi, 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 C-18-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 mi 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 mi 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 (ArO)-Ar-40-O-16 On Fe-56. 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.