The use of a suppressor column for calcium removal in the determination of iron in water samples by collision cell ICP-MS

Abstract

The use of H₂ as reagent gas eliminates Ar-based interferences in the determination of Fe by collision cell ICP-MS. However, natural water samples may contain high levels of calcium, which interfere in iron determinations by forming CaO⁺ and CaOH⁺ polyatomics that are not completely eliminated in the cell. In order to eliminate such Ca interferences on Fe, a conductivity suppressor column from a conventional ion chromatography system was connected between the pump and the ICP-MS nebuliser. Calcium removal by the suppressor column was higher than 99.99% for Ca concentrations up to 1000 ppm (sample pH between 2.5 and 7). In order to avoid the simultaneous removal of Fe, water samples were previously spiked with the chelating agent EDTA to form a negatively charged complex which is not destroyed in the suppressor column. Mineral water samples containing up to 260 mg l⁻¹ of Ca were analysed and the method allowed the interference-free determination of low ppb levels of Fe.