Abstract

We have developed a method for the determination of Cr(III) and Cr(VI) by ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) using a self-regenerating suppressor. Deposition of the dissolved solids on the cones and the ion optics was eliminated by the suppressor. Chromium(III) was derivatized with EDTA, forming a stable mono-anionic complex, which was then separated from Cr(VI) by anion-exchange chromatography. The conditions for the quantitative conversion of Cr(III) to the corresponding EDTA complex were optimized and neither oxidation of Cr(III) to Cr(VI) nor reduction of Cr(VI) to Cr(III) were observed. Using 50 mmol L⁻¹ NH₄NO₃ (pH 8) as the chromatographic eluent, potential interferents, such as chloride, carbonate and sulfate, were separated from both the Cr(EDTA)⁻ complex and from Cr(VI), and no salt deposition was observed over long periods of time. The tolerance of the method to the presence of major matrix anions (NO₃⁻, Cl⁻, CO₃²⁻ and SO₄²⁻) was extensively studied. With a 1 mL injection volume, the detection limits were 5 and 12 ng L⁻¹ using ⁵²Cr, and 7 and 16 ng L⁻¹ using ⁵³Cr for Cr(III) and Cr(VI), respectively. The RSD of 5 injections was less than 5% at the 50 ng L⁻¹ level. The method was validated using reference materials SRM 1643d and SLEW-3.