Determination of the isotopic composition of micrometric uranium particles by UV femtosecond laser ablation coupled with sector-field single-collector ICP-MS

Abstract

In this article, performance of the coupling of a UV-fs-LA system with a high sensitivity ICP-MS for isotope analysis of individual micrometric uranium particles, including minor isotopes 234U and 236U, is discussed.

Determination of the isotopic composition of single sub‐micrometer‐sized uranium particles by laser ablation coupled with multi‐collector inductively coupled plasma mass spectrometry

“…For all the isotopic ratios ( 234 U/ 238 U, 235 U/ 238 U and 236 U/ 238 U), the average relative biases were lower than 1%. Such values were better than those previously obtained with single‐collector ICPMS (1.1% and 1% for the 235 U/ 238 U ratio, 3% and 4% for the 234 U/ 238 U and 236 U/ 238 U ratios, respectively) and were close to what could be expected when the LA device is coupled with multi‐collector ICPMS (0.5% and −0.9% for the 235 U/ 238 U ratio). The relative biases are lower by a factor 2 to 4 in the cases of the 234 U/ 238 U and 236 U/ 238 U isotopic ratios than the relative external precision and the relative combined standard uncertainties.…”

“…Assuming that the particles were spherical, devoid of porosities and made of UO 2 , we calculate that 235 U and 234 U isotopes could be detected in 30 and 110 nm diameter particles, respectively. These diameters are roughly five times smaller than those reported by Donard et al [15] Such differences in the limit of detection are probably due to a higher sensitivity of the LA‐ICPMS instrumentation, both because of the higher intrinsic measurement yield of the LA‐MC‐ICPMS instrument used in this study than the single‐collector sector field ICPMS instrument used by Donard et al, but also because of the implementation of a “wet” plasma interface which provides a higher sensitivity than the “dry” plasma used by Donard et al Indeed, the sensitivity obtained for uranium by Donard et al in dry plasma conditions for a point ablation of the NIST 610 glass with fs‐UV‐LA‐ICP‐SF‐MS is ~39,000 cps/ppm while the sensitivity obtained in this study for a point ablation of the NIST 614 glass with ns‐UV‐LA‐MC‐ICPMS is ~3,950,000 cps/ppm, i.e. ~ 100 times higher.…”

“…It should be noted that Donard et al used another formula based on a Poisson distribution . We cannot apply the same formula since in this study the background does not follow the Poisson distribution.…”

“…Even with a pre‐localization step, the analysis of single uranium particles is still a challenge, mostly because of the small quantity of material available for the analysis. In most publications, the particle sizes were at least of 1 μm, whereas only three publications focused on the analysis of sub‐micrometer particles, which are by far the most abundant in environmental samples. Pointurier et al analyzed sub‐micrometer uranium particles with a nanosecond laser ablation (ns‐LA) device coupled to a quadrupole‐based ICP mass spectrometer.…”

“…Moreover, the trueness and precision were limited due to sequential measurements of the two isotopes with a single ion counter. Donard et al succeeded in measuring the major ( 235 U/ 238 U) and minor ( 234 U/ 238 U and 236 U/ 238 U) isotopic ratios in particles ranging from 0.5 to 1.6 μm and only the 235 U/ 238 U ratio in particles ranging from 0.3 to 0.5 μm by using a more sensitive method (single‐collector double‐focusing sector field ICPMS or ICPSFMS). However, the major issue was the biases caused by the use of single‐collector ICPMS which limited the trueness of the method.…”