Sector field ICP-mass spectrometry for the routine determination of uranium in urine

A method was developed for the quantification of U in urine by means of sector field ICP-mass spectrometry. To make the method suitable for epidemiological studies, reliability had to be combined with a high sample throughput. As a result, the sample pre-treatment was limited to 10-fold dilution with 0.14 M HNO3, while external standardisation was preferred over standard additions or isotope dilution for calibration. Use of a properly selected internal standard (Re) and optimisation of the carrier gas flow rate, aiming at a minimisation of the effect of the matrix on the signal ratio of the U-238(+), signal intensity to that of the internal standard Re-187(+), permitted accurate results to be obtained. The reliability of the method developed was demonstrated by the successful analysis of a certified reference material (BCR-668 Mussel Tissue) and a consequent near to 100% recovery for a 50 ng/L spike added to urine. The result for non-spiked pooled urine (U content of 1.6 ng/L) only varied within narrow and acceptable boundaries (+/- 10%). The limit of detection was established to be 0.2 ng/L, while the sensitivity amounted to 2000 counts/s per ng/L. At a level of 10 ng/L, the precision is typically 5% relative standard deviation. Per sample, the acquisition time is less than three minutes, permitting the analysis of approximately 100 samples in an 8h-working day. A pilot study showed that selection of the vessel material is not without importance, as some materials were shown to give rise to an unacceptably high blank level. Urinary U concentrations of approximately 3-4 ng/L, corresponding to 2-3 ng / g creatinine, seem to be typical for non-exposed individuals in Belgium and the Netherlands, although some values (