Quantitative Measurement of Rare Earth Elements in Brines: Isolation from the Charged Matrix Versus Direct LA‐ICP‐MS Measurements – A Comparative Study

Abstract

The quantification of the rare earth elements (REEs) in natural rocks and fluids is important not only for the sustainable use of geological resources but also for fundamental geological research. Due to significant improvements in experimental, modelling and analytical techniques, it was discovered that the REEs could be efficiently mobilised and transported by hydrothermal fluids. Thus, determining the REEs in fluids, especially in highly saline solutions, is a prerequisite to understand their fate in hydrothermal fluids. An analytical methodology was established to determine the trace quantities of the REEs in aqueous solutions with compositions typical to seawater and brines. The developed protocol was applied for the quantification of REEs in experimental sodium‐rich carbonate‐bearing hydrothermal solutions. For this purpose, we used two analytical approaches: (a) the REEs were chromatographically isolated from the charged matrix and introduced into a single collector quadrupole ICP‐MS and (b) direct determination of the REEs by LA‐ICP‐MS in experimental solutions loaded into glass capillaries without any additional isolation procedure. Both LA‐ICP‐MS and solution nebulisation ICP‐MS analysis after isolation of the REEs provide identical data in terms of REE concentrations in brines and are consistent within analytical uncertainties. Being an express method, LA‐ICP‐MS can be recommended for REE quantification in brines. At the same time, isolation of the REEs from the charged matrix with subsequent ICP‐MS measurement provides higher accuracy and precision, giving additional information for the REEs mass fractions that are below the detection limit of the LA‐ICP‐MS that was estimated at the ~ 10 ng g−1 level.