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

Abstract

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.