海水U、Th长寿命核素的高精密度MC-ICP-MS测定方法  

Long-lived U and Th high precision measurement method of MC-ICP-MS in seawater

作　　者：刘燕娜[1] 蔡毅华[2] 邢娜[2] 

机构地区：[1]厦门大学环境与生态学院,福建厦门361102 [2]厦门大学海洋与地球学院,福建厦门361102

出　　处：《应用海洋学学报》2015年第2期291-300,共10页Journal of Applied Oceanography

基　　金：国家自然科学基金资助项目(41276063);中国大洋协会国际海域资源调查与开发"十二五"资助项目(DY125-13-R-06)

摘　　要：建立了适合海水U、Th同位素高精密度测量要求的MC-ICP-MS方法.确定了采用Mg(OH)2共沉淀法富集海水U、Th同位素时的最佳NH3·H2O浓度为0.14 mol/dm3.采用CRM-145 U标准溶液,经质量分馏、电子倍增器增益、丰度灵敏度、仪器及试剂本底和记忆效应等校正后,历时3个月得235U/238U和234U/238U的准确度分别优于0.05%和0.08%,精密度分别优于0.12%和0.10%.将该方法应用于台湾海峡B9站位3份平行水样中U、Th同位素含量及比值的测定,得238U平均含量为3.05±0.05μg/kg,234U/238U平均值为(6.28±0.11)×10-5,U含量及其同位素比值的标准偏差均小于3%;232Th的平均含量为(1.66±0.04)×103pg/kg,232Th/230Th平均值为(1.95±0.01)×105,Th含量及其同位素比值的标准偏差均小于2%.测定结果与海区的水文学条件及物质来源相吻合,证明了方法的可靠性.A high precision method has been developed for analyzing uranium and thorium in seawater by MC-ICP-MS in this study.The optimal ratio of NH3＆#183;H2 O with acidified seawater of pH =2 （0.14 mol /dm3 ）is quantified for Mg（OH）2 coprecipitation protocol.The instrument and solvent background,abundance sensitivity,memory effects,mass fractionation and IC gains are properly corrected using CRM-145 U standard.Overall,the accuracy of 235U /238U and 234U /238U are better than 0.05% and 0.08% with precisions better than 0.12% and 0.10%,respec-tively,in about 3 month measurements of CRM-145 U standard.This method has been successfully applied to ana-lyze triplicate surface seawater samples from the Taiwan Strait.The average concentrations of 238U and 232Th are 3.05 ±0.05μg/kg and （1.66 ±0.04）×103 pg/kg,respectively,while the average ratios of 234U /238 U and 232Th /230Th are （6.28 ±0.11 ）×10 -5 and （1.95 ±0.01 ）×105 ,respectively.The standard deviations are less than 3% for U isotopes and 2% for Th isotopes.The results are consistent with hydrological characteristics and iso-topic provenance in the study area,which support the reliability of the method.

关 键 词：海洋化学 海水 铀 钍 

分 类 号：P734[天文地球—海洋化学]