Short-Pulse LA-MC-ICP-MS Measurement of Sr Isotopes: Application to the Quasi “Non-Destructive” Differentiation between Saltwater and Freshwater Pearls

Abstract

A rapid, minimally destructive method for in situ determination of Sr isotope ratios (⁸⁷Sr/⁸⁶Sr) using short-pulse laser ablation multi-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) coupled with linear regression calibration is presented. The ablation lasts only one second, causing minimal surface damage (~ 7 μm depth, 60 μm diameter). A carbonate matrix reference material for Sr isotope measurement (GIC-P, containing approximately 470 μg g⁻¹ Sr), fabricated from pressed pearl nanopowder, has been developed for data quality control and validation. Analysis of GIC-P using the proposed short-pulse LA-MC-ICP-MS method yielded results consistent with thermal ionisation mass spectrometry values. This method is ideal for analysis of valuable jewellery samples, as it ensures minimal destruction, high throughput, and cost efficiency while maintaining accuracy and precision, with intermediate precision quantified at better than 0.0004 (2s). When applied to market samples originating from China, Japan, French Polynesia and the South Pacific, the method confirms that saltwater pearls exhibit ⁸⁷Sr/⁸⁶Sr ratios consistent with modern seawater (~ 0.7092), whereas freshwater pearls show higher and more variable ratios (0.7102–0.7135 in this study), reflecting their growth environments in the freshwater of the middle and downstream regions of the Yangtze River, China. This distinct isotopic difference provides a reliable geochemical tool for differentiating between saltwater and freshwater pearls.