Capabilities of laser ablation – ICP-TOF-MS coupling for isotopic analysis of individual uranium micrometric particles

Capabilities of laser ablation coupled to a time of flight ICP-MS (‘icpTOF’, Tofwerk) for direct isotopic analysis of U micrometric reference particles deposited on carbon disks were demonstrated. Thanks to the very high temporal resolution which allows quasi simultaneous measurement of all nuclides, the icpTOF is well-suited for the acquisition of the very short transient signals produced by laser ablation of μm-sized particles. With appropriate corrections of the background due to high peak tailing of the 238U isotope and selection of signals within the detector's linear range, excellent internal and external precisions (0.2–0.4%) for measurement of the 235U/238U ratios were obtained in the most favorable cases (same abundances for the two isotopes). These precisions are better than the values reported until now in the literature, even with laser ablation coupled with multi-collector ICP-MS (MC-ICP-MS). For particles from other reference materials with low abundances of 235U, equal or close to the one of natural U, precisions for 235U/238U ratio measurements (4–5%) were not as good as the ones reported for MC-ICP-MS, but better than the ones obtained with single collector ICP-MS. Minor isotope ratios (234U/238U and 236U/238U) were also successfully measured, although with limited precision and accuracy when the abundances of the minor isotopes are very low, in the 10−5 range. This work shows that laser ablation coupled to ICP-TOF-MS has a great potential for ultra-precise isotope ratio measurements provided that the ablated area contains enough analyte and that abundances between isotopes are of the same order of magnitude.