Determination of 238U/235U, 236U/238U and uranium concentration in urine using SF-ICP-MS and MC-ICP-MS:: An interlaboratory comparison

Accidental exposure to depleted or enriched uranium may occur in a variety of circumstances. There is a need to quantify such exposure, with the possibility that the testing may post-date exposure by months or years. Therefore, it is important to develop a very sensitive test to measure precisely the isotopic composition of uranium in urine at low levels of concentration. The results of an interlaboratory comparison using sector field (SIF)-inductively coupled plasma-mass spectrometry (ICP-MS) and multiple collector (MC-ICP-MS for the measurement of uranium concentration and U-235/U-238 and U-236/U-231 isotopic ratios of human urine samples are presented. Three urine samples were verified to contain uranium at 1-5 ng L-1 and shown to have natural uranium isotopic composition. Portions of these urine batches were doped with depleted uranium (DU) containing small quantities of U-236, and the solutions were split into 100 mL and 400 mL aliquots that were subsequently measured blind by three laboratories. All methods investigated were able to measure accura tely U-238/U-235 With precisions of similar to 0.5% to similar to 4%, but only selected MC-ICP-MS methods were capable of consistently analyzi ng U-236/U-238 to reasonable precision at the similar to 20 fg L-1 level of U-236 abundance. Isotope dilution using a U-233 tracer demonstrates the ability to measure concentrations to better than +/- 4% with the MC-ICP-MS method, though sample heterogeneity in urine samples was shown to be problematic in some cases. MC-ICP-MS outperformed SF-ICP-MS methods, as was expected. The MC-ICP-MS methodology described is capable of measuring to similar to 1 % precision the U-238/U-235 of any sample of human urine over the entire range of uranium abundance down to < 1 Ing L-1, and detecting very small amounts of DU contained therein.