Strontium isotope ratio (87Sr/86Sr) is widely used in the fields of earth science, astrochemistry, environmental chemistry, food origin traceability, archaeology and so on. Thermoionization mass spectrometers (TIMS) have been regarded as the benchmark technique for 87Sr/86Sr ratio analysis since the 1960s. This method not only has excellent accuracy, but also has extremely high sensitivity. Excellent sensitivity is the prerequisite for high precision 87Sr/86Sr ratio analysis of ultramicro samples. The key to improve the sensitivity lies in the selection of an appropriate launcher to improve the ion yield of Sr+ on the surface of the metal ribbon. Traditional methods mainly use tantalum fluoride as an initiator, but tantalum cannot meet the analytical requirements of ultra-fine samples (≤200pg). Although the high resistance energy of the new 1013 partially makes up for the lack of sensitivity, However, its narrow dynamic signal detection range, long attenuation time, complex correction technology and high price restrict the wide assembly and application of 1013 high resistance. This technical bottleneck restricts the development of related disciplines.
Recently, Li Haofeng, a senior professor in the Solid Isotope Laboratory of the Institute of Geology and Geophysics, Chinese Academy of Sciences, and his collaborators found that using silicotungstate acid as the transmitter and Re filament as the sample carrier, the ultrafine Sr samples (30-200pg) can be analyzed with high precision at 87Sr/86Sr. Silicotungstic acid has three significant advantages: the sensitivity of silicotungstic acid is increased by 3 times, the Sr ion yield can reach ~16%, while the Sr ion yield of tantalum is only ~5%. It is easy to prepare and purify. Silicotungstic acid is a water-soluble solid powder, which can be purified by cationic resin after being dissolved in highly pure water. Silicotungstic acid is environmentally friendly and non-corrosive, while tantalum fluoride is corrosive to a certain extent and can only exist stably in hydrofluoric acid medium.
Related research results have been published in Analytical Chemistry.