利用多接收器电感耦合等离子体质谱法精确测定天然岩石样品中的铼含量

Precise Measurement Re Concentration of Natural Rock Sample by MC-ICPMS Using Iridium to Correct for Mass Fractionation

利用多接收器电感耦合等离子体质谱(MC-ICPMS)精确测定了天然岩石样品的铼含量。在膜除溶雾化进样条件下,铼测试样品中加入铱标准溶液,通过在线监控铱同位素的质量分馏行为来校正铼同位素的质量分馏。实验发现,铼和铱的质量分馏系数(fRe和fIr)是不相等的,如果认为fRe=fIr,将会导致187Re/185Re同位素比值偏低,但是fRe/fIr比值固定不变,这样可以通过已知的fIr计算出fRe,从而得到准确的187Re/185Re同位素比值。本工作利用这种经验的质量分馏校正方法,精确的测定出天然铼标准样品的187Re/185Re同位素比值为1.674 3±0.000 1(2,σn=25),该结果与国际纯粹与应用化学委员会(IUPAC)推荐值(1.674 0±0.001 1)以及与N-TIMS测定值(1.675±0.001 4)在误差范围内一致。而且,采用该经验的质量分馏校正方法测得的天然铼标准样品的187Re/185Re同位素比值与采用fRe=fIr校正结果相比,准确度和外部重现性都明显提高。最后采用该方法准确测定出了天然岩石中Re含量,该结果与N-TIMS测定结果吻合。

This study reported a measurement method of high-precision rhenium isotope ratio, ^187 Re/^185 Re, and Re concentration of natural rock samples were measured by multi-collector inductively coupled plasma mass spectrometry （MC-ICPMS） through measuring the amount of fractionation on admixed Iridium. It recognizes that the mass fractionation of MC-ICPMS appears to follow the exponential law, and the fractionation coefficients of Re and Ir are not identical, but the ratio of fRe/fIr is constant during an analytical session. Thus, this constant ratio can be used to calculate the value of fRe according to known value fIr. Replicate analyses of both Re natural standard and ^185Re-enriched spike determined by MCICPMS are consistent with those measured by negative thermal ionization mass spectrometry （N-TIMS）. ^187Re/^185Re ratios of the Re natural standard is 1. 674 3±0. 000 1（2σ, n=25）. The value is indistinguishable within analytical uncertainty from the value adopted by IUPAC （1. 674 0±0. 001 1）, and is also in agreement with those measured by N-TIMS （1. 675 5±0.001 4） . In addition, the precise and accurate are improved by usirig this empirical correction technique. The Re concentration of the natural rock samples are reasonable agree with those measured by N-TIMS.