Rapid unseparated rare earth element analyses by isotope dilution multicollector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS)

We present a method for analyzing rare earth elements (REEs) by isotope dilution without separation of individual elements. Utilizing a Nu Plasma 2 multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) equipped with an Aridus II desolvation nebulizer, sample introduction tuning parameters (torch position, gas flows) were investigated and used to minimize oxide formation (e.g., NdO/Nd <0.05%) and obviate the need to analyze the REEs as separated cuts. Ratios for spike isotopes relative to reference in mixed elemental standards containing varying amounts of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb were measured accurately within 1% of IUPAC values. La and Lu in the standards deviated more than 2% from expected values due to more pronounced interferences reducing the efficacy of corrections. A USGS (United States Geological Survey) BCR-2 rock standard was also processed with flux fusion, iron coprecipitation and bulk REE separation by a single column pass followed by analysis. The concentrations for Ce, Nd, Sm, Eu, Dy, Er, and Yb fell within 2% of consensus values. A USGS BIR-1A rock standard was also processed in triplicate by hydrofluoric and nitric acid digestion followed by iron coprecipitation and a single ion exchange column pass, yielding rare earth concentrations within 3% of consensus values with 0.3% relative standard deviation (n = 3). This demonstrates the ability to produce high quality REE patterns of comparable quality to traditional methods which require labor and time intensive REE separation, but with sample preparation and analytical times that are comparable to isotope dilution analyses by single-collector ICP-MS. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study presents a method for analyzing rare earth elements (REEs) by isotope dilution without the need for separating individual elements, demonstrating its reliability and accuracy. Compared to traditional methods, this approach eliminates time-consuming REE separation steps while ensuring the accuracy and stability of the analysis results.