Improved ion-exchange column chromatography for Cu purification from high-Na matrices and isotopic analysis by MC-ICPMS
Measurements of Cu isotopes from low concentration and high salinity matrices require high recovery and purity, prior to measurement. An automated two-stage chromatographic procedure, combining a pre-purification stage to remove the majority of matrix elements (AG® 50W-X12), with an adaptation of an existing method using anion exchange resin AG®MP-1 has been used to overcome these problems. A series of matrices were tested, from low (river water) to high salinity (synthetic seawater, human serum), using several standards and reference materials such as Trace Metals 1 (−0.21‰ ± 0.08 2SD), SLRS-5 (+0.30‰ ± 0.05 2SD), Seronorm™ (−0.25‰ ± 0.04 2SD), and NASS-7 seawater, doped with ERM®-AE633 (0.00‰ ± 0.14 2SD). Results demonstrated highly pure (>98%) Cu separations, low procedure blanks (<1% of loaded Cu), and much improved measurement reproducibility of <0.14‰ (2SD) for high salinity samples. This is an important development for δ65Cu measurement from low Cu concentrations commonly encounted in research of medical isotope metallomics, mineral exploration, and environmental geochemistry. As with other studies, combining standard-sample bracketing with Ga for internal normalisation to correct instrumental mass bias (C-SSBIN) resulted in a significant improvement in the precision of measurements (versus standard sample bracketing alone), typically improving the external reproducibility of measurements from 0.10 down to 0.03‰ (2SD).