Separation of magnesium from meteorites and terrestrial silicate rocks for high-precision isotopic analysis using multiple collector-inductively coupled plasma-mass spectrometry

Abstract

We report a modified procedure for separating Mg and Al from meteorites and terrestrial igneous rocks for high-precision analysis of Mg isotopes with multiple collector-inductively coupled plasma-mass spectrometry. The separating procedure was carried out in a single ion-exchange column filled with AG50W-X12 resin, and Mg was eluted with 1 M HNO₃, followed by Al eluted with 4M HNO₃. The modified procedure efficiently eliminates most matrix elements (except for Ni, Co, and Cu) with a recovery yield of Mg > 99%. Measurements of Ni-, Co-, and Cu-bearing simulation solutions revealed no detectable matrix effects. However, test runs demonstrated significant mass-dependent fractionation during the chromatographic process; consequently, a high recovery yield of Mg (>99%) is required to limit the deviation to less than 0.05‰. Furthermore, analysis of Mg standard solution with a wide range of concentrations demonstrated negligible deviation for samples with concentrations of 0.3–2.5 μg ml⁻¹Mg relative to Mg standard solution concentrations of 1 μg ml⁻¹Mg. The total procedure bank is less than 2 ng. The long-term reproducibility of instrumental measurements of Mg isotopes is ±0.05‰ for δ²⁵Mg, ±0.10‰ for δ²⁶Mg, and ±0.06‰ for δ²⁶Mg* (2 SD, n = 211), based on analyzing five pure Mg standard solutions. Analysis of three chondrites and seven igneous rock standards showed ranges of δ²⁶Mg_(DSM3) from 0.02‰ to 0.30‰ for the former and from 0.03‰ to 0.30‰ for the latter. This method is simple and actionable.