Determining Picogram Quantities of U in Human Urine by Thermal Ionization Mass Spectrometry

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Abstract
The U concentration in Standard Reference Material 2670 (Toxic Metals in Freeze-Dried Urine) and the urine of two preschool-age children were determined by measuring the chemically separated U by isotope dilution thermal ionization mass spectrometry using ion counting detection. This procedure can detect about 1% of the U atoms loaded into the mass spectrometer and has a total chemical blank of about 5 pg U. The U concentration in SRM 2670 was found to be 113 ± 2 pg 238U/ml (1 s). At this concentration, a 1-ml sample is sufficient for a determination with a total uncertainty of less than 5%. The U concentrations in the two children were 3.1 ± 0.9 and 3.6 ± 0.9 pg 238U/g. These values suggest that the U concentration in urine of unexposed persons may be at this low level or lower.