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),, methylselenocysteine (SeMCys) and provide detection limits between 0.10 and 0.19 mg 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 mg g À1 creatinine; range: 0.47-8.97 mg g À1 creatinine) and SeSug3 (0.80; 0.07-3.53 mg 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 mg Se per g creatinine) and SeMCys (0.13; 0.03-0.41 mg 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 mg 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.D-glucosamine (SeSug2) and methyl-2-amino-2-deoxy-1-seleno-b-D-galactopyranoside (SeSug3), are major urinary eliminated selenium metabolites. 11-15 Furthermore, Klein et al.

Selenium metabolism to the trimethylselenonium ion (TMSe) varies markedly because of polymorphisms in the indolethylamine N-methyltransferase gene

“…One of the methylated selenium metabolites is the trimethylselenonium ion (TMSe), 8 which has been identified in some selected human urine samples by using HPLC coupled to inductively coupled plasma mass spectrometry [HPLC/ICPMS (8)(9)(10)(11)(12)]. The further-developed HPLC/vapor generation (VG)/ ICPMS method allows the selective determination of TMSe at concentrations w1 order of magnitude below that of conventional HPLC/ICPMS (13).…”

Human metabolism and renal excretion of selenium compounds after oral ingestion of sodium selenate dependent on trimethylselenium ion (TMSe) status

“…Concentrations above the calibration range were diluted with water and were analyzed again. Validation of the methods had been carried out for all analytes (see Jäger et al 2013 for full validation data). The limit of detection (LOD) was determined to be 0.10 μg Se/L for SeVI, SeSug3, SeMet, SeMCys, 0.11 μg Se/L for SeEt, 0.16 μg Se/L for TMSe and 0.18 μg Se/L for SeMG.…”

“…Urine samples were digested with HNO 3 , HCl and H 2 O 2 in a Microwave 3000 digestion system (Anton Paar, Graz, Austria). Selenium concentration in the digests was determined with an Agilent 7500cx ICP-MS (Agilent Technologies, Santa Clara, CA, USA) equipped with a Micromist nebulizer, a Scott spray chamber and nickel cones analyzing 78 Se under reaction cell gas mode using 4.5 ml/min H 2 (Jäger et al 2013). Accuracy of total selenium determination was proved by the analysis (n = 3) of standard reference material (SRM) 2670a (freeze-dried urine, National Institute of Standard and Technology, Gaithersburg, USA) with the following results: low level 91 ± 6 % (reference value: 8 ± 3 μg/L) and high level 86 ± 6 % (reference value: 229.5 ± 8.3 μg/L).…”

“…All other commercial reagents were used at analytical reagent grade. Speciation analysis was performed by HPLC-ICP-MS according to the procedures of Jäger et al (2013) using three different separation techniques. In brief, ion pairing chromatography was used for the quantification of SeSug1, SeSug3, SeMet, SeMG and SeEt using a reverse phase column (Phenomenex Luna C18(2); 150 × 4.6, 3 μm) and sodium-1-butanesulfonate as ion pairing reagent.…”

“…Kuehnelt et al (2006) described for the first time that considerable amounts of TMSe were detected in human urine occasionally. Finally, Jäger et al (2013) reported a dichotomous distribution of humans regarding the ability to generate TMSe. In 20 % of urine samples of the German population, a distinct concentration of TMSe was detected, whereas the majority does not excrete TMSe in detectable levels.…”