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

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.