A Novel Alkali Precipitation Method for Tungsten Separation and High‐Precision Isotopic Measurement in Geological Samples

Abstract

Tungsten (W) isotopes are useful tools in geological and cosmochemical research, but the chemical separation of W is cumbersome for high‐precision measurement. Here, a novel alkali (sodium hydroxide, NaOH) precipitation method for separation and purification of W in geological samples is described, which simplifies the chemical procedure. The amphoteric character of W is exploited to separate it from most matrix elements in alkaline conditions. Subsequently, TEVA resin was applied to further purify W for measurements using a multi‐collector inductively coupled plasma‐mass spectrometer. Importantly, the introduction of a certain amount of Na in the W analyte can increase the signal intensity by approximately 1.6 times, which may be caused by Coulomb fission. Such Na‐triggered signal enhancement reduces the test portion mass required for analysis. Our results show that the Alfa Aesar W standard solution and geological reference materials JB‐3, BCR‐2 and BHVO‐2 yield 182W/184W ratios consistent with previously reported values within uncertainty. Repeated measurement of the Alfa Aesar W standard solution shows that the intermediate precision of 182W/184W was better than 5 ppm (2s), which is sufficient to identify subtle 182W isotope variations in terrestrial and extra‐terrestrial samples. Above all, the alkali precipitation method in this study optimises the experimental process and mass spectrometric analysis.