微量萤石样品消解技术及其Sm-Nd同位素高精度热离子质谱法测试

Micro-fluorite Sample Digestion Technology and High Precision Thermionic Mass Spectrometry Determination for Sm-Nd Isotopes

Sm-Nd同位素被广泛地应用于萤石样品的定年和示踪。萤石样品Sm-Nd同位素测试的化学分离中,一般采用酸溶解样品,但氢氟酸和硝酸与萤石反应不完全,由于萤石(CaF_2)特殊化学结构导致氟离子会和稀土元素离子形成难溶稀土氟化物,易导致Sm-Nd亏损,因而对于Sm、Nd含量较低的萤石样品,Sm-Nd同位素测试需要较大样品用量(100~200 mg)。本研究建立了一种利用HNO_3+HClO_4+H_3BO_3溶解萤石样品的消解方法,在萤石溶解过程中加入H_3BO_3可有效提高Sm-Nd回收率。实验表明,利用5 mL浓硝酸和0.015 mL高氯酸溶解萤石样品过程中加入1 mL 0.49 mol/L H3BO3效果最佳,结合高灵敏度热电离质谱仪(Triton)可实现微量萤石样品高精度Sm-Nd同位素测试。较先前已有的溶解方法,本方法大大降低萤石样品用量。

The Sm-Nd isotopic system is widely used in the isotopic dating and tracing of fluorite. In the process of chemical separations for the Sm-Nd isotope analysis, fluorite is dissolved by acid regularly, but it does not react with the hydrofluoric acid and nitric acid. Additionally, the special chemical structure of fluorite （CaF2） often leads to the insoluble rare earth fluoride produced by fluoride ion and rare earth ion, which results in the loss of Sm and Nd in the sample. Therefore, a large sample dosage （100-200 mg） is usually designed to meet the demands of the Sm-Nd isotope analysis in the fluoride with low content of Sm and Nd. In this study, the authors established a new experimental method to dissolve fluoride by using the HNO3＋HC104＋H3BO3 solvent system. In this system, the application of H3BO3 is effective in improving the recovery of Sm and Nd in the fluoride. Furthermore, the experiments also show that adding 1 mL 0.49 mol/L H3BO3 in the mixed system of 5 mL concentrated nitric acid and 0.015 mL percholric acid has the best effect on the dissolution of fluoride. Combined with high sensitive thermal ionization mass spectrometer （Triton）, the high accuracy Sm-Nd isotopic analysis of fluoride micro-samples could be realized. Compared with the conventional method, this method can reduce the dosage of fluoride sample obviously.