Determination of five selenium compounds in urine by liquid chromatography with focused microwave assisted digestion and hydride generation–atomic absorption spectrometric detection

Abstract

A method is proposed for the determination of trimethylselenonium ion, selenomethionine, selenocystine, selenite and selenate in urine, following clean-up with C 18 cartridges. The on-line system developed consists of an anion-exchange chromatographic column for species separation, a focused microwave oven for the oxidation of organic Se species in the presence of 3% K 2S 2O 8 and 3% NaOH solution and reduction of selenate to selenite in 10 mol l −1 HCl, a hydride generation system for the conversion of selenite to selenium hydride and finally an atomic absorption spectrometer detector. Optimum chromatographic conditions were obtained in a Hamilton PRP-X100 column, using 100 mmol l −1 phosphate buffer (pH=6.8) as the mobile phase. Detection limits were between 3 and 8 μg l −1. The relative standard deviation was <7% at 100 μg l −1 Se. The short-term stability test of the studied Se species in urine shows after 5 h of storage about 30% and 60% losses of selenite and SeCys, respectively. After taking pills containing Se about 60% of the Se ingested is excreted in the first 12 h. Se(VI) ingested is partially excreted as Se(VI) and partially transformed and excreted as a species that behaves as SeCys. SeMet is metabolised and excreted as species that behave as Se(VI) and SeCys.