Ion pairing and ion exchange chromatography coupled to ICP-MS to determine selenium species in human urine

Abstract

In this work three analytical methods were developed and applied to determine a broad spectrum of selenium species in human urine. The methods are based on different liquid chromatographic separation techniques (ion pairing, anion exchange and cation exchange chromatography) coupled to an inductively coupled plasma-mass spectrometer (ICP-MS) for selenium specific detection. They were adjusted for the determination of nine species named selenate (Se(VI)), selenite (Se(IV)), trimethylselenium ion (TMSe), methylselenoglutathione (SeMeG), methyl-2-acetamido-2-deoxy-1-seleno-β-D-galactopyranoside (SeSug1), methyl-2-amino-2-deoxy-1-seleno-β-D-galactopyranoside (SeSug3), selenomethionine (SeMet), selenoethionine (SeEt), methylselenocysteine (SeMCys) and provide detection limits between 0.10 and 0.19 μg Se per L. The procedures were applied to 45 urine samples of individuals of the general population. SeSug1 was detected in 100% (median: 1.79 μg g⁻¹ creatinine; range: 0.47–8.97 μg g⁻¹ creatinine) and SeSug3 (0.80; 0.07–3.53 μg Se per g creatinine) in 80% of the study population. SeSug1 and SeSug3 were strongly correlated; however a shift of their relation was observed in dependence of the exposure level. In 20% of the samples compounds were detected, which could be related to Se(VI) (0.12; 0.03–1.12 μg Se per g creatinine) and SeMCys (0.13; 0.03–0.41 μg Se per g creatinine). TMSe was detected in 18% of the samples. But whenever TMSe was detected, it was found in considerable concentrations (2.91; 2.72–4.42 μg Se per g creatinine). The species SeMet, SeEt, SeMeG and Se(IV) were not detected in any of the samples. The results of the study are consistent with the literature in which SeSug1 is well-established as major selenium species in human urine since years. Moreover, the results show that the composition of urinary eliminated Se-species might change depending on the Se exposure level. Finally, the results indicate a polymorphic selenium metabolism related to the formation of TMSe.