Speciation analysis of selenium in human urine by liquid chromatography and inductively coupled plasma mass spectrometry for monitoring of selenium in body fluids

Abstract

Speciation analysis of selenium metabolites in urine was performed using hyphenation of mixed ion-pair reversed-phase chromatography and inductively coupled plasma mass spectrometry. A chromatographic separation was performed with a C8 stationary phase and a mobile phase containing 2.5 mmol L−1 sodium butane-1-sulfonate, 8 mmol L−1 tetramethylammonium hydroxide, 4 mmol L−1 malonic acid, and 0.05% methanol, pH 3.0. Under this condition, the selenium species selenite, selenate, selenomethionine, selenoethionine, selenourea, trimethylselenonium, and Se-methylselenocysteine were successfully separated. Selenium determination was carried out by monitoring 80Se. The internal standard Ge was added into the mobile phase. The calibration was linear at least up to 100 μg L−1 Se for all species. The limit of detection was 0.4 μg L−1 Se. When higher (1400 W) ICP power was applied, the calibration based solely on selenate provided accurate results for all species. Stability tests revealed extremely short stability of selenite. After collection, the urine samples should be acidified to pH 3.0, stored below –5 °C, and analyzed before 12 h after collection. The method was used for the short-time (single capsule, one day observation, 5 persons) monitoring of the excretion of selenium after ingestion of Se-containing dietary supplements. When a formulation containing selenate was applied, almost 50% of Se was excreted during 24 h (mostly in the unchanged form of selenate) and the plasma Se remained unaltered. In the case of organically bound Se, only 8% of Se was lost by urination during 24 h as selenite, Se-methylselenocysteine, selenomethionine, and unknown species. Subsequently, a statistically significant increase of plasma Se was observed.