title: Precise determination of U isotopic compositions in low concentration carbonate samples by MC-ICP-MS.
abstract: We developed a fast and simple analytical procedure for precise determination of U isotopic compositions in low concentration natural samples. The main advantage of the new method is that it requires only 12ng U and can obtain all U isotopic ratios without using spike. Five carbonate reference materials (JCp-1, RKM-4, RKM-5, GBW04412 and GBW04413) and 3 international standards with different matrices (IAPSO, IRMM-3184 and CRM-U010) were analyzed for ((234)U/(238)U) and (238)U/(235)U ratios by MC-ICPMS. Using our method, the results for these standards are in close agreement with the certified values, 1.144 ± 0.004, 0.966 ± 0.004 and 0.990 ± 0.003 for ((234)U/(238)U) and 137.72 ± 0.13, 137.64 ± 0.15 and 98.63 ± 0.04 for (238)U/(235)U, in IAPSO, IRMM-3184 and CRM-U010, respectively. The long-term reproducibility of ((234)U/(238)U) and (238)U/(235)U is 0.970 ± 0.002 and 137.56 ± 0.09; 1.144 ± 0.004 and 137.72 ± 0.13, respectively, for in-house U solution and IAPSO. The new ((234)U/(238)U) results for carbonates show much better precision than previous studies and also reflect their age variability. The obtained (238)U/(235)U ratios, representing the first measurements in these carbonate specimens, are rather constant. The method described here requires only 12 ng of U for analysis and can be completed in 5.2 min. The approach provides a fast method to measure ((234)U/(238)U) and (238)U/(235)U ratios in sample matrices commonly encountered in studies of chemical weathering, oceanography and paleoclimatology.
authors.affiliation: Department of Earth Sciences, National Cheng Kung University, No.1, University Road, Tainan 701, Taiwan.
authors.forename: Ruo-Mei
authors.initials: RM
authors.lastname: Wang
authors.forename: Chen-Feng
authors.initials: CF
authors.lastname: You
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D013058:Mass Spectrometry / Q000191:economics / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013997:Time Factors; D014501:Uranium / Q000032:analysis* / Q000302:isolation & purification
chemical_list: D002254:Carbonates; D014501:Uranium