Precise Determination of the Molybdenum Isotopic Composition of Urine by MC-ICP-MS.

Rationale: Molybdenum (Mo) is predominantly expelled from the human body in urine. Consequently, urinary variability in the concentration and isotopic composition of Mo may encode valuable clinical information. To access this information, however, it is first necessary to develop and demonstrate a rapid, accurate and precise methodology capable of concentrating Mo from urine for isotope analysis. Methods: The utility of N-benzoyl-N-phenylhydroxylamine (BPHA) to effectively separate and purify Mo from urine samples without the need for acid digestion was tested. Following this approach, applying a double-spike mass bias correction, we determined the Mo isotopic compositions of a set of urine samples by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Results: Based on replicate analyses of an in-house urine standard, this approach demonstrates an external precision on delta Mo-98/95 values of better than 0.08 parts per thousand (2SD, n = 15). Application to a sample set collected from healthy individuals in Guangzhou, China, provides the first suite of delta Mo-98/95 measurements from urine samples. Samples from the female participants show delta Mo-98/95 (parts per thousand) values (1.31 +/- 0.19 parts per thousand, Ave +/- 2SD, n = 14) that are consistently lower than those from the male participants (1.55 +/- 0.16 parts per thousand, Ave +/- 2SD, n = 17). Conclusions: The employed methodology is suitable for rapid, low-blank and high-throughput Mo isotope analysis of urine samples. Although resolvable delta Mo-98/95 variability is seen in this preliminary dataset, the mechanism driving this variability is unknown. High-precision Mo isotopic analysis might be added to the urinalysis tool-kit, with the potential to provide valuable clinical information in the future.