Determination of thorium and uranium in urine with inductively coupled argon plasma mass spectrometry

An accurate and simple method has been developed for the determination of thorium and uranium in urine using inductively coupled argon plasma mass spectrometry (ICP-MS). Determination of thorium and uranium was by external calibration using matrix matched standards and high-purity spiking materials. Aliquots of each urine specimen were diluted (1 + 9) with 0.2 mol l–1 nitric acid containing iridium as an internal standard. The counts at m/z 232 (thorium), 238 (uranium) and 193 (iridium) were measured, and ratios of the counts at m/z 232 or 238 to those at m/z 193 were calculated. These ratios were compared with those from urine-based calibration standards to calculate the thorium and uranium concentrations in unknown specimens. The concentrations of thorium and uranium were calculated as µg l–1 in the sample and also corrected for dilution via creatinine measurement, expressed as µg g–1 of creatinine. The method has been evaluated by determination of reference materials from the Los Alamos National Laboratory, as well as of those from the Oak Ridge National Laboratory. The proposed method provides the basis of an accurate method for determining thorium and uranium in unexposed subjects as well as in those considered to be exposed to thorium or uranium through environmental or other pathways. About 40 specimens, excluding blanks, calibration standards and quality-control materials, can be processed in an 8 h day.