Simultaneous speciation of endogenous and exogenous elements by HPLC/ICP-MS with enriched stable isotopes

High performance liquid chromatography (HPLC)/ inductively coupled argon plasma-mass spectrometry (ICP-MS) was introduced to investigate the distributions of selenium (Se) in biological fluids. The method was to determine both the natural abundance of Se and an enriched stable isotope of Se used as a tracer. The distributions of Se in plasma and in urine specimens were determined in Wistar rats on various Se diets with and without an intravenous injection of 82Se-selenite. Although the distribution of natural abundance Se (endogenous Se) in the plasma was affected little by the nutritional status of Se, that in the urine gave a Se peak depending on the nutritional status of Se, and the peak was identified as methylselenol. When 82Se-selenite was injected in excess into rats given three different Se diets (Se-deficient, Se-adequate, Se-excessive), three Se peaks occurred in the HPLC chromatogram of the urine samples, corresponding to selenite, methylselenol and trimethylselenonium ion in the order of elution, and the intensities of the tracer peaks reflected the nutritional status. These results indicate that the HPLC/ICP-MS method is a powerful analytical tool for specifying Se-containing biological constituents, both natural abundance and enriched stable isotopes. Methylselenol in urine is proposed to be a sensitive and Se-specific biological indicator for diagnosing the nutritional status of Se. Furthermore, it was shown that an enriched stable isotope such as 82Se-selenite was shown to be used for the same purpose, and that 82Se-methylselenol and 82Se-trimethylselenonium ion in urine were more sensitive indicators of the Se status of the rats.