离子交换分离过程中铅同位素分馏评估及针对MC-ICPMS铅同位素测定的分离纯化方法的修正

Pb isotopic fractionation during the ion exchange process and the modification of purification methods for isotope determination by MC-ICPMS

本文对分离纯化样品过程中铅同位素的分馏进行了评估,并描述了适于MC-ICPMS同位素测定的分离纯化方法。利用AG1-X8阴离子交换树脂分离纯化样品中铅的过程确实导致了铅同位素的质量分馏。尽管分离纯化过程导致的铅同位素分馏程度较小(0.43‰amu-1),但明显超出了仪器的测试误差(0.23‰amu-1),如果样品中铅的回收率太低,会导致铅同位素测试值明显偏离真值。利用AG1-X8阴离子交换树脂,以0.2mL 1mol/L HBr溶液为上样介质,以5mL 1mol/L HBr和0.5mL 2mol/L HCl溶液为淋洗液,1.5mL 6mol/L HCl溶液为洗脱液,利用该分离流程可以保证获得样品中铅同位素的准确值。在本实验研究条件下,相对于过柱前样品,前期淋洗液富集铅的轻同位素(δ208Pb<0),后期淋洗液富集铅的重同位素(δ208 Pb>0),表明在该实验条件下,铅的重同位素组分比轻同位素更容易和树脂结合,AG1-X8阴离子交换树脂吸附铅的配分系数208 D/204 D大于1。解吸被树脂吸附铅的过程中,铅在不同络合形式间的交换反应可能导致了铅同位素的分馏效应,意味着无机络合物或者有机大分子参与反应的过程可能会导致铅同位素的分馏。

In this paper, the fractionation of Pb isotope during the purification procedure is assessed, and the pu- rification methods for isotope determination by MC-ICPMS are described. Purification procedure indeed leads to the mass fractionation of Pb isotope through AG1-X8 anion exchange resin. Though the fractionation is very small （0.43%0 amu-1）, it is beyond the instrument error apparently （0.23%o amu-1）. The very low recovery of Pb during the purification procedure would cause Pb isotope value to deviate from the real value. With AG1- X8 as exchange resin, 0.2 mL 1 mol/L HBr solution as loading solution, 5 mL 1 mol/L HBr and 0.5 mL 2 mol/ L HC1 solution as eluent for cleaning up the impurities, and 1.5 mL 6 mol/L HCl solution as eluent for desorption of the Pb adsorbed by the resin, the value determined after the purification of sample by using the separation procedure would be close to the true value within error. Under such a condition, the early fractions of the eluate are systematically enriched in the light isotopes （δ208Pb〉0）, whereas the late fractions of the eluate are systematically enriched in the heavy isotopes （δ208Pb〉0）, which indicates that the heavy Pb isotopes partition is absorbed more strongly into the resin than the lighter isotopes, and the distribution coefficient of Pb absorbed into the resin 20SD/204D〉1. Pb isotope fractionation may happen with the exchange of Pb in different types of complex compound in the desorption process, which implies that Pb isotope fractionation would occur in the reaction including inorganic compound or organic macromolecules. The results achieved by the authors not only enrich the knowledge of Pb isotope fractionationbut also provide more information for the analysis and application of Pb isotopes.