Determining picogram quantities of uranium in urine by isotope dilution inductively coupled plasma mass spectrometry. Comparison with α-spectrometry

Abstract

An accurate and simple method has been developed for the determination of uranium in urine using inductively coupled plasma mass spectrometry (ICP-MS). Isotope dilution analysis was applied using the long-lived uranium nuclide ²³³U as a spike in 1.3-fold diluted urine samples. To avoid matrix effects and salt depositions in the interface region of the instrument a prototype concentric-flow nebulizer with a mini cyclonic spray chamber was used at a reduced sample uptake rate of 0.3 ml min⁻¹. The method was evaluated by comparison with α-spectrometry, as well as by analysis of National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2670, Toxic Metals in Freeze Dried Urine, for which published results of isotope dilution thermal ionization mass spectrometry (TIMS) and radiochemical neutron activation analysis (RNAA) measurements are available. ICP-MS and α-spectrometry yielded consistent results (Wilcoxon, p = 0.87). The ICP-MS mean value (±95% confidence interval) of 143 ± 10 pg ml⁻¹ obtained for the SRM 2670 agreed with the reported RNAA value of 130 ± 18 pg ml⁻¹ at the 95% confidence interval; however, they exceeded the reported TIMS value of 113 ± 3 pg ml⁻¹. The proposed method provides a means for determining uranium in unexposed subjects as well as in those considered to be exposed. Potential exposure to uranium amongst employees of UNHCR in western Kosovo was assessed.