Demonstration of isotope pattern screening for selective detection of selenium-containing compounds by LC-Q-Orbitrap-MS

Selenium (Se) is an essential trace metal in animals and a beneficial trace metal in plants. Many unknown Se-containing compounds exist in nature, and they have beneficial functions, including antioxidant properties. However, liquid chromatography-inductively coupled plasma mass spectrometry, the primary tool for Se speciation analysis, cannot identify unknown Se-containing compounds, and new technologies of qualitative analysis are needed. In this study, we demonstrate an isotope pattern screening (IPS) technique for the selective detection of Se-containing compounds such as seleno-l-methionine, selenohomolanthionine, methylselenocysteine (MeSeCys), 1β-methylseleno-N-acetyl-d-galactosamine, and trimethylselenonium by liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS). IPS was able to detect Se-containing compounds in biological matrices, such as water, blood, urine, plant extract, and culture medium. Furthermore, utilizing LC-ESI-MS, we identified a novel Se-containing metabolite, N-(1-carboxyethyl)-S-(methylselanyl)cysteine, in the culture medium of gut bacteria exposed to MeSeCys. IPS is applicable to other elements, such as tellurium and zinc, which have characteristic isotope patterns. The new technique of qualitative analysis, IPS with LC-ESI-MS, is expected to contribute to research in bio-inorganic chemistry and metal biology because IPS is applicable to other elements with multiple isotopes.