植物样品中低水平铀同位素分析

摘要

An analytical method was developed for determination of low-level uranium isotopes in vegetation samples. Dry ashing method was employed to decompose organic matters of vegetation. The sample ash was further digested using multiple acids. Uranium in the prepared sample solution was separated and purified by an extraction chromatography using UTEVA resin. The chemical recovery of uranium in the separation procedure was more than 94% , and more than 99% of Na, K, Ca and other matrix elements and interfering elements were removed. Three natural uranium isotopes were finally measured with high sensitivity ICP-MS/MS. The detection limits of the method for 238U, 235U, 234U were 3. 05, 0. 34 and 0. 04 pg/g, respectively. The detection limits for 238U and 235U were 10 times better than the reported values. Analysis result of U in GBW-10046 standard reference material was in good agreement with reference value, indicating that this method was reliable. The method was successfully applied to determination of uranium isotopes in the vegetation samples collected in Xi′an region, and it was found that the uranium concentrations and isotopic ratios in these vegetation samples fall well into natural level, and there was no significant artificial uranium contamination. This was the first survey of the three natural uranium isotopes in vegetation samples in this region.%建立了一种植物样品中痕量铀同位素( 238U、235U和234U)的分析方法.通过高温灰化去除植物样品中有机质,采用混合酸消解样品灰分,应用UTEVA萃取色谱分离和纯化铀.化学分离过程中铀的回收率达94% ,对Na、K、Ca等基体和干扰元素的去除率超过99% .用高灵敏度ICP-MS/MS同时测定了3种天然铀同位素含量,对238U、235U、234U的检出限分别为3. 05、0. 34和0. 04 pg/g,其中对238U和235U的检出限比文献报道值低1个数量级.对小麦粉标准参考物质中238U的分析结果与参考值吻合,表明本分析方法可靠.将本方法应用于中国西安地区植物样品中铀同位素的分析,结果表明,该地区植物中铀含量和铀同位素比值处于天然水平,未发现人为铀污染.这是中国植物样品中3种天然铀同位素水平的首次调查.