Determination of Depleted Uranium in Urine via Isotope Ratio Measurements Using Large-Bore Direct Injection High Efficiency Nebulizer—Inductively Coupled Plasma Mass Spectrometry

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS), coupled with a large-bore direct injection high efficiency nebulizer (LB-DIHEN), was utilized to determine the concentration and isotopic ratio of uranium in 11 samples of synthetic urine spiked with varying concentrations and ratios of uranium isotopes. Total U concentrations and 235U/238U isotopic ratios ranged from 0.1 to 10 μg/L and 0.0011 and 0.00725, respectively. The results are compared with data from other laboratories that used either α-spectrometry or quadrupole-based ICP-MS with a conventional nebulizer–spray chamber arrangement. Severe matrix effects due to the high total dissolved solid content of the samples resulted in a 60 to 80% loss of signal intensity, but were compensated for by using ²³³U as an internal standard. Accurate results were obtained with LB-DIHEN– ICP-MS, allowing for the positive identification of depleted uranium based on the ²³⁵U/²³⁸U ratio. Precision for the ²³⁵U/²³⁸U ratio is typically better than 5% and 15% for ICP-MS and α-spectrometry, respectively, determined over the concentrations and ratios investigated in this study, with the LB-DIHEN–ICP-MS system providing the most accurate results. Short-term precision (6 min) for the individual ²³⁵U and ²³⁸U isotopes in synthetic urine is better than 2% (N = 7), compared to ∼5% for conventional nebulizer–spray chamber arrangements and >10% for α-spectrometry. The significance of these measurements is discussed for uranium exposure assessment of Persian Gulf War veterans affected by depleted uranium ammunitions.