电感耦合等离子体质谱法测定土壤钍含量以及记忆效应的研究

目的 建立微波消解-电感耦合等离子体质谱(ICP-MS)测定土壤中钍含量的分析方法,研究了检测过程中钍的记忆效应及消除记忆效应的方法,并分析我国9种土壤中的钍含量。方法 以Pt为内标元素,补偿检测过程中的基体效应。分别采集不同浓度的钍元素溶液,研究钍元素的记忆效应,以及有效消除钍记忆效应的方法。结果 随着样品中钍含量的升高,记忆效应显著增强,增加清洗剂中的硝酸浓度,钍的记忆效应逐渐降低,采用5% HNO₃(V/V)清洗能有效消除钍元素的记忆效应。检测条件优化后,钍元素回收率为89.5%~102.9%,方法检出限为0.6 μg/L,r=0.9999。对土壤标准品进行分析,测得值与标准参考值相吻合,相对误差< 3%。采用该方法分析我国9种典型土壤中的钍含量,均值在2.48~8.02 mg/kg之间。结论 本研究建立的微波消解-电感耦合等离子体质谱法分析土壤中钍含量的方法准确度高、检测限低,回收率好。钍元素在检测过程中有明显的记忆效应,采用5%硝酸溶液作为清洗剂可有效消除钍的记忆效应。采用该方法分析我国9种土壤中的钍含量均在正常水平。

Determination of Thorium in Soil by Inductively Coupled Plasma Mass Spectrometry and Study of Thorium Memory Effect in Analysis

Objective A method involving microwave digestion and inductively coupled plasma-mass spectrometric (ICP-MS) analysis was established for the determination of thorium in soil. Thorium memory effect in analysis and the method to eliminate the memory effect were studied. Methods Pt was confirmed as the internal standard to compensate matrix influence. Three kinds of solutions containing different concentration of Th were analyzed respectively, to study the thorium memory effect, and to find the rinse solutions to eliminate the thorium memory effect. Results The higher content of thorium in solution, the better obvious memory effect became. Addition of nitric acid to rinse solution eliminated the Th memory effect, and blank level counts were achieved after 1.5min wash-outs with 5% (V/V) HNO₃. Detection limit for thorium was 0.6 μg/L, and the recovery ranged from 89.5% to 102.9%. The cps ratio of Th and Pt is linear with the thorium concentration (r=0.9999). The accuracy of this method is corrected using standard soils, and the analytical results are in good agreement with certified values by RSD < 3%. The thorium contents in nine kinds of soils in China had been determined with the developed method, and the contents ranged from 2.48 mg/kg to 8.02 mg/kg. Conclusion The analysis method to determine the thorium concentration in the soil turns out to be accurate, sensitive and efficient. During determination of thorium concentration the memory effect could be found, and 5% nitric acid would be useful for eliminating it. The thorium concentration in nine kinds of soils in China detected using the method was all in normal range.