Separation and determination of seleno amino acids using gas chromatography hyphenated with inductively coupled plasma mass spectrometry after hollow fiber liquid phase microextraction

Compilation of selenium metabolite data in selenized yeasts

Selenium-enriched yeast has long been recognized as an important nutritional source of selenium and studies have suggested that supplementation with this material provides chemo-preventative benefits beyond those observed for selenomethionine supplementation, despite the fact that selenomethionine accounts for 60-84% of the total selenium in selenized yeasts. There is much ongoing research into the characterization of the species comprising the remaining 16-40% of the selenium, with nearly 100 unique selenium-containing metabolites identified in aqueous extracts of selenized yeasts (Saccharomyces cerevisiae). Herein, we discuss the analytical approaches involved in the identification and quantification of these metabolites, and present a recently created online database (DOI: 10.4224/40001921) of reported selenium species along with chemical structures and unique mass spectral features.

Evaluation of different strategies for determination of selenomethionine (SeMet) in selenized yeast by asymmetrical flow field flow fractionation coupled to inductively coupled plasma mass spectrometry (AF4-ICP-MS)

This manuscript exemplifies the prospective use of asymmetrical flow field flow fractionation (AF4) coupled to inductively coupled plasma mass spectrometry (ICP-MS) as a simple tool for chemical speciation of selenomethionine (SeMet) in selenized yeast. Several popular sample preparation methods were evaluated for their suitability to determine selenomethionine (SeMet) in selenized yeast by AF4-ICP-MS. These included water, methanesulfonic acid (MSA), formic acid (FA) and alkaline extractions. Alkaline extraction (using sodium dodecyl sulfate buffer) provided the best recovery/determination conditions for SeMet based on analysis of NRC certified reference material (CRM) SELM-1 since it minimized hydrolysis of the protein peptide bonds optimally required for the AF4 separation. The analytical performance of three different AF4 membranes (5, 10 and 500 kDa regenerated cellulose) was also evaluated. No significant difference in the recovery of SeMet was observed when using 5 and 10 kDa RC membranes, whereas the 500 kDa membrane resulted in a significant loss. The proposed method presents appropriate instrument and intra-assay precisions of 4.4-9.2% and 3.8% RSD, respectively, a detection limit of 0.49 μg L-1 SeMet as Se and good linearity with correlation coefficients (R) between 0.996 - 0.999. This is the first report of use of AF4-ICP-MS for species specific quantitation of SeMet in selenized yeast demonstrating its efficient use as an alternative method to other traditional chromatographic techniques.

Simultaneous determination of five essential amino acids in plasma of Hyperlipidemic subjects by UPLC-MS/MS

BACKGROUND

Millions of adults have been reported with hyperlipemia in the world. It is still unclear whether the plasma level of essential amino acids (AAs) will be influenced by the hyperlipemia. This study was aimed to investigate the AAs levels and the underlying metabolic relationship in hyperlipidemic subjects.

METHODS

An ultra-high performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method was developed for the determination of phenylalanine (Phe), valine (Val), histidine (His), tryptophan (Trp), and methionine (Met). Plasma samples (100 μL) were precipitated by acetonitrile (300 μL) and analyzed on a BEH C18 (2.1 mm × 100 mm, 1.7 μm) column at 40 °C by gradient elution. The mobile phase composed of 0.1% formic acid and acetonitrile was used with flow rate at 0.2-0.4 ml/0-3 min. Five AAs were determined at positive electrospray ionization (ESI+) at m/z 118.1/72.1 (Val), 150.12/104.02(Met), 156.06/110.05(His), 166.1/120.1(Phe), and 205.2/188.02 (Trp). A total of 75 healthy subjects and 83 hyperlipidemic subjects, who had blood routine test and plasma lipid test were determined by developed UPLC-MS/MS.

RESULTS

It was shown that there was good linearity for Val, Met, His, Phe, and Trp within 1-100 μg/mL. The relative standard deviations of precision and accuracy were all within 15%. The level of Val, Phe, Trp, His, and Met were 35.34 ± 15.64, 22.72 ± 9.13, 17.23 ± 4.94, 16.78 ± 13.64, and 6.24 ± 1.97 μg/mL in healthy subjects, while they were 38.04 ± 16.70, 22.41 ± 8.45, 15.62 ± 5.77, 18.35 ± 14.49, and 6.21 ± 1.97 μg/mL in hyperlipidemic subjects respectively. The Spearman's correlations analysis showed that there were high correlations between Val, Phe, Trp, His, Met and triglyceride in healthy subjects. While, those correlations decreased in hyperlipemia cases.

CONCLUSION

A convenient and sensitive method for simultaneous determination of Val, Phe, Trp, His, and Met in human plasma was developed. There was a high correlation between Val, Phe, Trp, His, Met and triglyceride. Hyperlipemia influences the metabolic balance of His, Phe, Trp, Met and Val.

Recent Microextraction Techniques for Determination and Chemical Speciation of Selenium

Research designed to improve extraction has led to the development of microextraction techniques (ME), which involve simple, low cost, and effective preconcentrationof analytes in various matrices. This review is concerned with the principles and theoretical background of ME, as well as the development of applications for selenium analysis during the period from 2008 to 2016. Among all ME, dispersive liquid-liquid microextraction was found to be most favorable for selenium. On the other hand, atomic absorption spectrometry was the most frequently used instrumentation. Selenium ME have rarely been coupled to spectrophotometry and X-ray spectrophotometry methods, and there is no published application of ME with electrochemical techniques. We strongly support the idea of using a double preconcentration process, which consists of microextraction prior to preconcentration, followed by selenium determination using cathodic stripping voltammetry (ME-CSV). More attention should focus on the development of accurate, precise, and green methods for selenium analysis.

Analysis of amino acids in tobacco by derivatization and dispersive liquid-liquid microextraction based on solidification of floating organic droplet method

A new one-step derivatization and microextraction technique was developed for determination of amino acids in tobacco samples. In the proposed method, amino acids were derivatized with isobutyl chloroformate (IBCF) in aqueous solution. The derivatives were extracted by dispersive liquid-liquid microextraction based on solidification of floating organic droplet (DLLME-SFO). Parameters affecting the extraction efficiency were investigated in detail. The optimum conditions were as follows: a mixture of 500μL acetone, containing 40μL 2-dodecanol, was rapidly injected by syringe into the 2mL water sample. After centrifugation, the 2-dodecanol droplets were floated at the top of the tube. Then, the tube was cooled in an ice bath. After 5min the solvent had solidified and was then transferred into a conical vial; it melted quickly at room temperature and it was injected into a gas chromatograph for analysis. Under the optimum conditions, the limits of detection were of the order of 0.12-2.82μg/mL. The calibration curves showed good linearity over the investigated concentration range between 0.5 and 200μg/mL with a coefficient of estimation (R(2))>0.9887 for GC-MS (SIM). The proposed method is an alternative approach to the quantification of amino acids in tobacco samples.

A reliable solid phase microextraction-gas chromatography-triple quadrupole mass spectrometry method for the assay of selenomethionine and selenomethylselenocysteine in aqueous extracts: difference between selenized and not-enriched selenium potatoes

A new analytical approach is exploited in the assay of selenium speciation in selenized and not selenium enriched potatoes based on the widely available solid-phase microextraction (SPME) coupled to-GC-triple quadrupole mass spectrometry (SPME-GC-QqQ MS) method. The assay of selenomethionine (SeMet) and selenomethylselenocysteine (SeMeSeCys) in potatoes here reported provides clues to the effectiveness of SPME technique combined with gas chromatography-tandem mass spectrometry, which could be of general use. For the exploitation of the GC method, the selected analytes were converted into their N(O,S)-alkoxycarbonyl alkyl esters derivatives by direct treatment with alkyl chloroformate in aqueous extracts. The performance of five SPME fibers and three chloroformates were tested in univariate mode and the best results were obtained using the divinylbenzene/carboxen/polydimethylsiloxane fiber and propylchloroformate. The variables affecting the efficiency of SPME analysis were optimized by the multivariate approach of design of experiment (DoE) and, in particular, a central composite design (CCD) was applied. Tandem mass spectrometry in selected reaction monitoring (SRM) has allowed the elimination of matrix interferences, providing reconstructed chromatograms with well-resolved peaks and the achievement of very satisfactory detection and quantification limits. Both precision and recovery of the proposed protocol tested at concentration of 8 and 40 μg kg(-1) (dry matter), offered values ranging from 82.3 to 116.3% and from 8.5 to 13.1% for recovery and precision, respectively. The application of the method to commercial samples of selenized and not selenium enriched potatoes proved that the Se fertilization increases significantly the concentration of these bioavailable selenoamino acids.

Surveying selenium speciation from soil to cell--forms and transformations

The aim of this review is to present and evaluate the present knowledge of which selenium species are available to the general population in the form of food and common supplements and how these species are metabolized in mammals. The overview of the selenium sources takes a horizontal approach, which encompasses identification of new metabolites in yeast and food of plant and animal origin, whereas the survey of the mammalian metabolism takes a horizontal as well as a vertical approach. The vertical approach encompasses studies on dynamic conversions of selenium compounds within cells, tissues or whole organisms. New and improved sample preparation, separation and detection methods are evaluated from an analytical chemical perspective to cover the progress in horizontal speciation, whereas the analytical methods for the vertical speciation and the interpretations of the results are evaluated from a biological angle as well.