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| Determination of Thorium in Soil by Inductively Coupled Plasma Mass Spectrometry and Study of Thorium Memory Effect in Analysis |
| GUO Zhi-ying, LIANG Yue-qin, CUI Xiao-lei, YU Shui |
| Biomedical Analysis Center, Academy of Military Medical Sciences, Beijing 100850 China |
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Abstract 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.
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Received: 12 August 2012
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