High-Precision Determination of the 238U/235U Isotope Ratio in Rocks by Multicollector Inductively Coupled Plasma Mass Spectrometry
- 47 Downloads
The paper describes the high-precision U-isotope analysis of rocks. The analysis is based on multicollector inductively coupled plasma mass spectrometry (MC−ICP−MS) and includes, as an essential part, the three-step ion-exchange chromatography separation of uranium from chemically complex solutions. In the analysis, the 235U and 238U mass-bias of the MC−ICP−MS is corrected against the reference ratio of 233U and 236U in a double-spike added. The doublespiking precedes sample chemical digestion. This approach is useful as it corrects isotope data for a possible U-isotope fractionation that could have occurred in the chemical preparation of samples. The double-spike 236U/233U is 1.03183 ± 0.00005. The extraction procedure ensures uranium yield of more than 80%. The accuracy of the analysis was estimated by the study of 238U/235U in an international standard sample IRMM-3184 as well as in monitor samples. The uncertainty was estimated at ±0.008% (2SD), which is comparable with the accuracy of the results previously published by foreign researches. The analysis was elaborated for studying natural 238U/235U ratio variations. It was used by the authors for the high-precision determination of the U-isotope composition in rocks (granites, shales, volcanic rocks) and U-bearing minerals.
Keywords:inductively coupled plasma mass spectrometry MC−ICP−MS isotopes 238U and 235U rocks
This work was supported by the Russian Science Foundation, project no. 16-17-10221.
We are grateful to M.V. Muravyev and N.I. Serdyuk for technical provision of the work of mass spectrometers.
- 1.Proceedings of an International Symposium on the Oklo Phenomenon, Libreville, Gabon, West Africa, 1975.Google Scholar
- 9.Golubev, V.N., Chernyshev, I.V., Chugaev, A.V., Eremina, A.V., Baranova, A.N., and Krupskaya, V.V., Geol. Rudn. Mestorozhd., 2013, no. 6, p. 1.Google Scholar
- 13.Pupyshev, A.A. and Sermyagin, B.A., Diskriminatsiya ionov po masse pri izotopnom analize metodom mass-spek trometrii s induktivno svyazannoi plazmoi (Discrimination of Ions by Mass in Isotopic Analysis by Inductively Coupled Plasma–Mass Spectrometry), Yekaterinburg, 2006.Google Scholar
- 20.Nemerov, V.K., Stanevich, A.M., Razvozzhaeva, E.A., et al., Geol. Geofiz., 2010, vol. 51, no. 5, p. 729.Google Scholar