Uranium analysis in urine by inductively coupled plasma dynamic reaction cell mass spectrometry

Urine uranium concentrations are the best biological indicator for identifying exposure to depleted uranium (DU). Internal exposure to DU causes an increased amount of urine uranium and a decreased ratio of U-235/U-238 in urine samples, resulting in measurements that vary between 0.00725 and 0.002 (i.e., natural and depleted uranium's U-235/U-238 ratios, respectively). A method based on inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was utilized to identify DU in urine by measuring the quantity of total U and the U-235/U-238 ratio. The quantitative analysis was achieved using U-233 as an internal standard. The analysis was performed both with and without the reaction gas oxygen. The reaction gas converted ionized U-235(+) and U-238(+) into (UO2+)-U-235 (m/z = 267) and (UO2+)-U-238 (m/z= 270). This conversion was determined to be over 90% efficient. A polyatomic interference at m/z 234.8 was successfully removed from the U-235 signal under either DRC operating conditions (with or without oxygen as a reaction gas). The method was validated with 15 urine samples of known uranium compositions. The method detection limit for quantification was determined to be 0.1 pg U mL(-1) urine and an average coefficient of variation (CV) of 1-2% within the sample measurements. The method detection limit for determining U-235/U-238 ratio was 3.0 pg U mL(-1) urine. An additional 21 patient samples were analyzed with no information about medical history. The measured U-235/U-238 ratio within the urine samples correctly identified the presence or absence of internal DU exposure in all 21 patients.