An optimal method for magnesium purification and magnesium isotopic composition obtained by MC-ICP-MS

Abstract

We present a method to obtain high quality Mg isotopic data for rocks with diverse Mg concentrations by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). The separation efficiency of Mg is greatly improved by optimizing the acid molarity and column size and introducing HF in the eluting acid. The chromatographic separation uses a single column without additional procedures and efficiently achieves the purification of Mg from matrix elements including Na, K, Ca, Al, Fe, Ti, and K. The recovery of the purification method is 100.5% ± 1.4%. The effect of concentration mismatch and acid mismatch as well as the matrix effect were systematically tested by using a Nu Plasma 3 MC-ICP-MS in wet plasma mode. The average δ²⁶Mg of three synthetic standard solutions, prepared by doping mono-elemental Mg standard solutions Alfa-Mg, GSB-Mg, and IRMM-009 with matrix elements, agrees with the recommended values within error. The robustness and reproducibility of the established method were further examined by replicated measurements of reference materials including rock standards, seawater, and standard solutions. Biological reference materials GSB-14 and GSB-19 have for the first time been characterized for Mg isotopic composition. The long-term precision based on repeated measurement of standards is better than ±0.06‰ for δ²⁶Mg. Such precision and accuracy of Mg isotope measurement can be more widely used to obtain accurate Mg isotopic compositions of different samples, and to trace geochemical processes in future studies.