Quantification of methionine and selenomethionine in biological samples using multiple reaction monitoring high performance liquid chromatography tandem mass spectrometry (MRM-HPLC-MS/MS)

Determination of methionine and selenomethionine in food matrices by gas chromatography mass spectrometry after aqueous derivatization with triethyloxonium salts

A novel analytical method for the simultaneous gas chromatography-mass spectrometry (GC-MS) determination of methionine and selenomethionine in food samples is described. Samples were digested with methanesulfonic acid in a closed vessel without the need for reflux. A single step derivatization using triethyloxonium tetrafluoroborate was optimized for the conversion of the analytes into their ethyl derivatives, followed by their extraction with hexane and GC-MS analysis.. This derivatization approach was simpler and/or safer with respect to current methods based on alkyl chloroformate or silylating reagents and it yielded very clean chromatography. A design of experiment approach, based on an open source chemometric software, was used to optimize the experimental conditions. When analysis of a 1 mL volume of aqueous standard was performed, detection limits of 1 ng/g methionine and 10 ng/g for selenomethionine were obtained. The method was validated by analysis of a selenized yeast Certified Reference Material NRC SELM-1.

Derivatization-targeted analysis of amino compounds in plant extracts in neutral loss acquisition mode by liquid chromatography-tandem mass spectrometry

Amino compounds, such as amino acids and biogenic amines, are important metabolites that can be found in diverse natural matrices. The most common method for amino compound analysis nowadays is reversed-phase liquid chromatography tandem mass spectrometry (RPLC-MS/MS). However, due to the polar and the basic nature of amines, their RPLC retention is often insufficient or peaks are tailing. Derivatization is a way to overcome the issue and in the present work amino compounds are derivatized with diethyl ethoxymethylenemalonate (DEEMM) and analyzed by a RPLC triple quadrupole MS system in neutral loss scan (NLS) mode (loss of 46). This allows to target all compounds in the sample that undergo derivatization with DEEMM, so that the amino compound profile of the sample is obtained. To the best of our knowledge, the NLS acquisition mode has never been employed to target amino compounds after DEEMM derivatization. In the first part of the study, eight amino acids (arginine, aspartic acid, threonine, proline, tyrosine, tryptophan, phenylalanine and isoleucine) were employed as model compounds for method optimization, with good results in terms of DEEMM derivatives detection and repeatability. The developed method was successfully applied to a complex extract from the plant species Carduus nutans subsp. macrocephalus (Desf.) Nyman, with 18 amino acids and 3 other amines being identified. The proposed approach could be employed for straightforward identification of known and unknown amino compounds in different types of matrices.

Tissue Distribution Study of Poloxamer188 in Rats by Ultra-High-Performance Liquid Chromatography Quadrupole Time of Flight/Mass Spectrometry with MSALL-Based Approach

Poloxamer188 (PL188), as one of the most commonly used pharmaceutical excipients, has unique physicochemical properties and good biocompatibility, and so is playing an increasingly extensive role in the field of medicine. Currently, there are few studies on the tissue distribution of PL188 in vivo. In this study, the LC-MS method based on MS^ALL technique of quadrupole time of flight mass spectrometry for absolute quantitative analysis of poloxamer 188 in biological substrates was established for the first time. The tissue distribution of poloxamer188 in SD rats were studied using the established quantitative analysis method. To explore the distribution of PL188 in organs and tissues, PL188 was administered via rat tail vein at a dose of 5 mg/kg. Eight kinds of tissues including heart, liver, spleen, lung, kidney, stomach, muscle and brain of rats were collected at 0.25 h, 1 h and 4 h after administration. Tissue distributions showed the highest level was observed in kidney, then in stomach, which indicated PL188 mainly bioaccumulated in the kidney. This study can provide references for the further study of PL188.

Raman Microspectroscopic Analysis of Selenium Bioaccumulation by Green Alga Chlorella vulgaris

Selenium (Se) is an element with many commercial applications as well as an essential micronutrient. Dietary Se has antioxidant properties and it is known to play a role in cancer prevention. However, the general population often suffers from Se deficiency. Green algae, such as Chlorella vulgaris, cultivated in Se-enriched environment may be used as a food supplement to provide adequate levels of Se. We used Raman microspectroscopy (RS) for fast, reliable, and non-destructive measurement of Se concentration in living algal cells. We employed inductively coupled plasma-mass spectrometry as a reference method to RS and we found a substantial correlation between the Raman signal intensity at 252 cm⁻¹ and total Se concentration in the studied cells. We used RS to assess the uptake of Se by living and inactivated algae and demonstrated the necessity of active cellular transport for Se accumulation. Additionally, we observed the intracellular Se being transformed into an insoluble elemental form, which we further supported by the energy-dispersive X-ray spectroscopy imaging.

A Research Strategy to Analyze the Major Chemical Constituents in Kudiezi Injection based on Mass Spectrometry and Chromatographic Techniques

Kudiezi injection was a commonly used drug in clinical practice, contained many components and was complex in structure. In order to effectively control the quality of traditional Chinese medicine, the study established a systematic research strategy for the first time. Through the UPLC-Q-TOF/MS technology analysis, 35 chemical components in Kudiezi injection were obtained, including four major categories. Moreover, the the quantitative methods of flavonoids by HPLC and organic acids by UPLC-MS/MS were established. A variety of chromatographic techniques, with good precision, sensitivity, repeatability and solution stability were applied to the analysis of 10 batches of Kudiezi injection. Therefore, the quality control of Kudiezi injection was a reliable and effective method, which can provide ideas for the qualitative and quantitative study of chemical constituents in other complex Chinese medicines.

Selenium Incorporation to Amino Acids in Chlorella Cultures Grown in Phototrophic and Heterotrophic Regimes

Microalgae accumulate bioavailable selenium-containing amino acids (Se-AAs), and these are useful as a food supplement. While this accumulation has been studied in phototrophic algal cultures, little data exists for heterotrophic cultures. We have determined the Se-AAs content, selenium/sulfur (Se/S) substitution rates, and overall Se accumulation balance in photo- and heterotrophic Chlorella cultures. Laboratory trials revealed that heterotrophic cultures tolerate Se doses ∼8-fold higher compared to phototrophic cultures, resulting in a ∼2-3-fold higher Se-AAs content. In large-scale experiments, both cultivation regimes provided comparable Se-AAs content. Outdoor phototrophic cultures accumulated up to 400 μg g^-1 of total Se-AAs and exhibited a high level of Se/S substitution (5-10%) with 30-60% organic/total Se embedded in the biomass. A slightly higher content of Se-AAs and ratio of Se/S substitution was obtained for a heterotrophic culture in pilot-scale fermentors. The data presented here shows that heterotrophic Chlorella cultures provide an alternative for Se-enriched biomass production and provides information on Se-AAs content and speciation in different cultivation regimes.

In vitro bioaccessibility of selenoamino acids from selenium (Se)-enriched Chlorella vulgaris biomass in comparison to selenized yeast; a Se-enriched food supplement; and Se-rich foods

Selenium (Se) is an indispensable microelement in our diet and health issues resulting from deficiencies are well documented. Se-containing food supplements are available on the market including Se-enriched Chlorella vulgaris (Se-Chlorella) which accumulates Se in the form of Se-amino acids (Se-AAs). Despite its popular uses, data about the bioaccessibility of Se-AAs from Se-Chlorella are completely missing. In the present study, gastrointestinal digestion times were optimized and the in vitro bioaccessibility of Se-AAs in Se-Chlorella, Se-yeast, a commercially available Se-enriched food supplement (Se-supplement) and Se rich foods (Se-foods) were compared. Higher bioaccessibility was found in Se-Chlorella (∼49%) as compared to Se-yeast (∼21%), Se-supplement (∼32%) and Se-foods. The methods used in production of Se-Chlorella biomass were also investigated. We found that disintegration increased bioaccessibility whereas the drying process had no effect. Similarly, temperature treatment by microwave oven also increased bioaccessibility whereas boiling water did not.