Selenium Species in Aqueous Extracts of Alfalfa Sprouts by Two-Dimensional Liquid Chromatography Coupled to Inductively Coupled Plasma Mass Spectrometry and Electrospray Mass Spectrometry Detection

Abstract

The complementary use of two different liquid chromatographic mechanisms coupled to inductively coupled plasma mass spectrometry (ICP-MS) for selenium (Se) specific detection has permitted the screening of the most abundant Se-containing fractions in selenized alfalfa sprouts (Medicago sativa). Aqueous extracts of the sprouts were fractionated first by size exclusion chromatography (SEC) using a Superdex Peptide column and a mobile phase containing an ammonium acetate buffer (pH 7). Further purification of the individual SEC Se-containing fractions was carried out using two different chromatographic systems: a Shodex Ashaipack column, with a mixed mechanism of size exclusion and ion exchange, and a conventional reversed phase C8 using ion-pairing reagents. In both cases, the columns were coupled to an inductively coupled plasma mass spectrometer equipped with an octapole reaction system for Se specific detection. This system allowed the on-line monitoring of the most abundant Se isotopes (78Se, 80Se) by reducing the possible polytomic interferences affecting these ions by adding hydrogen (2 mL min(-1)) to the octapole reaction cell. The results obtained by both separation mechanisms were highly comparable, revealing the presence of Se-methionine and Se-methyl selenocysteine. Both compounds were then confirmed by analyzing the corresponding fractions by electrospray quadrupole-time-of-flight (ESI-Q-TOF) mass spectrometry. Finally, an additional Se-containing species showing Se isotope distribution was detected at a molecular ion m/z 239 in the ESI-Q-TOF. The collision-induced dissociation of the m/z 239 and 237 ions (corresponding to 80Se and 78Se isotopes, respectively) revealed the possible presence as well of a derivative of the Se-2-propenyl selenocysteine.

Selenium Uptake and Biotransformation and Effect of Selenium Exposure on the Essential and Trace Elements Status: Comparative Evaluation of Four Edible Plants

“…On the other hand, an important beneficial effect of Se fortification was observed, Ni levels found in biomass decreased when plants were exposed to selenium. This protective effect of selenium against the uptake and toxicity of heavy metals has been described for several plant species [9,38,39]. Based on the results of this work, exposure of alfalfa to 1.0 mg Se L -1 in form of Se(IV) seems to be a good start for elaboration of natural dietary supplement; however, plant capacity to synthesize oSe should also be considered.…”

“…As indicated in introduction, MeSeCys, SeMet, gamma-glutamyl-methylselenocysteine are the main organic species reported in selenized plants [8,38]. Specifically, for radish SeMet, MeSeCys, (SeCys)2 were reported [21,22], for alfalfa SeMet, MeSeCys [39,40] and for sunflower SeMet [41], speciation analysis for chard have not been performed. On the other part, it is widely accepted that oSe contained in natural products is a better source for selenium supplementation as compared to iSe.…”

How to use the world's scarce selenium resources efficiently to increase the selenium concentration in food

“…It was also shown that sunflower sprouts were the most resistant and had the highest uptake rates (up to 900 mg/kg), but almost 100% of the Se was extracted with water and found to be non-metabolized selenate (155). Others have found that selenized alfalfa sprouts contain both Se-met and SeMCYS, and also an additional Se-containing species, a derivative of Se-2-propenyl selenocysteine, was possibly present (156).…”

Inorganic selenium speciation in environmental samples using selective electrodeposition coupled with electrothermal atomic absorption spectrometry

“…Separation techniques for elemental speciation can be generally classified into chromatographic and non-chromatographic techniques. The chromatographic techniques include high performance liquid chromatography [9], capillary electrophoresis [10], size exclusion chromatography (SEC) [11] and ion-chromatography [12]. Non-chromatographic separation techniques include solvent extraction [13], co-precipitation [14], cloud point extraction [15] and solid phase extraction (SPE) [16][17][18][19][20][21][22][23].…”

“…Because of the disadvantages of conventional extraction techniques, solvent-free sample preparation methods or those employing fewer organic solvents are becoming increasingly important. Combinations of general separation methods with various detection techniques such as X-ray absorption spectrometry [24][25][26], neutron activation analysis (NAA) [27][28][29], inductively coupled plasma optical emission spectrometry (ICP-OES) [10,[30][31][32] and inductively coupled plasmamass spectrometry (ICP-MS) [8,33], have been applied to measure trace selenium and its species in various samples. Although a high sensitivity is reported for these methods, they are very expensive and unavailable in many academic labs.…”