Determination of isotope fractionation of Cr(iii) during oxidation by LC/low-resolution MC-ICPMS

Abstract

A robust and sensitive method for the precise isotopic analysis of ⁵³Cr/⁵⁰Cr during Cr(III) oxidation by coupling ion pair reversed-phase chromatography and Multicollector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) is presented. The effective separation of Cr(III) and Cr(VI) species from a sample matrix by HPLC enables on-line isotopic determination of the ⁵³Cr/⁵⁰Cr ratio in transient signals by MC-ICPMS, without the laborious off-line and time consuming sample preparation step associated with a high probability of speciation changes. Mass discrimination and instrument drift were corrected by the sample-standard bracketing method using the ⁵³Cr/⁵⁰Cr isotope ratio of SRM 979 as the standard. The obtained results show good precision but are still approximately two-three times worse than the high precision results achieved by TIMS and MC-ICPMS with off-line Cr separation. Robustness, acceptable precision and accuracy, as well as a minimum possibility of sample contamination, of the developed analytical method have been demonstrated in complex natural samples of natural water (IAPSO standard water) and a standard spiked with several metal ions.