利用MC-ICPMS高精度测定地质样品的钛同位素组成的方法研究

High-precision Ti isotope measurement of geological reference materials using MC-ICPMS

由于高场强元素(HFSEs:Ti, Nb, Ta, Zr, Hf和W等)与HF有良好的亲和性,因此采用AG1-X8强阴离子树脂及HF淋洗可以实现地质样品中Ti、Nb、Ta、Zr、Hf和W等高场强元素与Ca、Cr、Mo和V等基体元素的分离;再利用Ln特效树脂可以分离Ti与其他的HFSEs,最后通过AG1-X8强阴离子树脂及HF淋洗可进一步对Ti与残留的Ca、Mg等进行分离,从而实现地质样品中Ti与基体元素的最大程度分离,并且可以获得近100%的Ti回收率。分离好的Ti溶液在多接收电感耦合等离子质谱(MC-ICPMS)上采用标准-样品-标准(SSB)的方法测量Ti同位素比值。利用样品相对于前后测量标准(NIST 3162a Ti solution)的万分偏差,获得地质标准样品相对于NIST 3162a的钛同位素组成(ε49Ti)。玄武岩标准物质BHVO-2的ε49Ti的外部精度可达到0.5ε,此结果与双稀释获得的精度相当。利用上述方法我们对一些地质标准物质的钛同位素组成进行了高精度的测试,结果显示地幔玄武岩具有较为均一的钛同位素组成,而较为演化的花岗岩钛同位素组成偏高,不同表生成因的锰结核与沉积物样品的钛同位素组成也有差异,但均介于地幔玄武岩与花岗岩之间。由此可见,不同地质过程会产生明显的钛同位素的分馏,这为我们利用钛同位素组成示踪不同地质过程的作用提供了可能。

Here,we present a new three-stage Ti separation procedure using AG1-X8and Ln resins.Ti isotopes of a number of geological reference materials were measured using MC-ICPMS calibrated by the standard-samplestandard bracketing method.Through the AG1-X8resin,Ti and other high-field-strength elements(HFSEs),such as Nb,Ta,Zr,Hf,and W,could be effectively separated from matrix elements,such as Ca,V,Mo,Cr,and other major elements.Ti could be separated from other HFSEs by Ln resin.The Ti recovery rate was close to100%,which was satisfactory to measure Ti isotopes using MC-ICPMS.The extra precision ofε49Ti for BHVO-2(basalt reference materials)was0.5εfor the past12months,which is close to that of the double-spike method.Ti isotopes of a number of geological reference materials were measured based on the above method.Basalts showed uniform Ti isotopes,whereas more evolved granites had higher Ti isotopes.The Ti isotopes of Fe-Mn nodules were between those of basalts and granites.The significant variation in Ti isotopes in different geological backgrounds provided a good proxy to trace the different geological processes.