锌同位素比值和含量的双稀释质谱测量法

THE MEASUREMENT OF THE ISOTOPE RATIOS AND CONCENTRATIOS OF ZINC BY THERMAL IONIZATION MASS SPECTROMETRY USING DUOBLE ISOTOPE DILUTION

用纯度９９．９９％的金属锌粉配制成一定含锌量的天然锌溶液作为测量富集（￣（５７）Ｚｎ、￣（７０）Ｚｎ）锌溶液含锌量的稀释剂，再用此富集锌作为测量待测锌的含锌量的双同位素稀释剂，使用磷酸硅胶热电离质谱技术分别测量天然锌、富集锌、待测锌、天然加富集锌和富集加待测锌五种样品的￣（６４）Ｚｎ、￣（６６）Ｚｎ、￣（６８）Ｚｎ和￣（７０）Ｚｎ对￣（６７）Ｚｎ的同位素比值。利用这些比值和混合锌溶液中稀释剂与富集或待测锌溶液的质量比，依据质量分馏效应修正和质量守恒规律建立矩阵方程，用迭代法求解稀释比Ｘｒ（稀释剂与富集或待测锌参考同位素ｒ的原子数比），稀释剂锌、富集或待测锌和混合锌同位素比值的分馏效应修正系数ｆ＿ｔ、ｆ＿ｎ和ｆ＿ａ，就能够计算出各种锌样品的同位素比值的修正值、富集锌和待测锌样品的含锌量。锌同位素比值、富集和待测锌样品含锌量测量的不确定度分别为±０．１６％、±０．２２％和±０．３１％。

The isotope ratios and concentrations of zinc are measured by silicagel-thermal ionizationmass spectrometry using the double isotope spikers. The double isotope spikers (￣(70)Zn and ￣(67)Zn-enriched isotopes) are used to correct the isotope mass fractionation for the zinc isotope ratios,andto certifv the zinc concentrations in the unknown samples. The zinc concentrations of these doubleisotope spikers are surveyed by a spiker made of pure(99. 99%)natural zinc metal powder. Thecorrecting factors (f_a、f_tandf_n)of the zinc isotope ratios in the spiked mixture,spike and un-spiked samples for the isotope mass fractionation,and the spike-to-unspiked ratios(X_r) of thezinc isotope r in the spiked mixture samples can be obtained to solve the matrix equations by nu-merical approximation.The natural zinc isotope ratios are:￣(64)Zn/￣(67)Zn=11. 8498,￣(66)Zn/￣(67)Zn=6.7977,￣(68)Zn/￣(67)Zn=4.5730 and￣(70)Zn/￣(67)Zn=0.1520. The uncertainies determined of the iso-tope ratios and concentrations of zinc are ±0. 16%and ±0.31%,respectivlely.