Chloroformates in gas chromatography as general purpose derivatizing agents

Decreasing matrix effects for accurate analysis of primary aliphatic amines in skin moisturizers using magnetic adsorbent

In this study, for analysis of primary aliphatic amines present in skin moisturizer samples, a dispersive micro solid phase extraction method using a mercaptoacetic acid-modified magnetic adsorbent (MAA@Fe3O4) was developed to eliminate matrix effects (while not adsorbing the studied analytes). This approach was combined with vortex-assisted liquid-liquid microextraction for the simultaneous derivatization and extraction of primary aliphatic amines present in these samples. To confirm the successful synthesis of the adsorbent, various characterization techniques were employed, including X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, scanning electron microscopy, Fourier transform infrared spectrometry, energy-dispersive X-ray, thermogravimetric analysis, and vibrating sample magnetometry. ComplexGAPI software and analytical eco-scale index were employed to evaluate the greenness of the method. All key parameters affecting matrix cleanup, derivatization, and extraction were optimized. A gas chromatograph equipped with a flame ionization detector was used for the identification and quantification of the amine derivatives. The method demonstrated high unadsorbed percentage of the analytes (92-97%), significant enrichment factors (420-525), wide linear ranges (1.6-10,000 µg L- 1), excellent precision (1.4-2.7%), and low limits of detection (0.5-0.82 µg L- 1). This approach offered several advantages, including eco-friendliness, short extraction time, high matrix removal efficiency, simplicity, excellent precision, no need for specialized equipment, and adsorbent reusability for up to five cycles. The method also proved highly effective in the simultaneous extraction and derivatization of amines, further highlighting its potential for analytical applications.

A biomarkers study of human skin fibroblasts exposition to glyphosate-based herbicide using an untargeted and targeted metabolomics approach

Metabolomics is a valuable tool to assess glyphosate exposure and its potential impact on human health. However, few studies have used metabolomics to evaluate human exposure to glyphosate or glyphosate-based herbicides (GBHs). In this study, an untargeted and targeted metabolomics approach was applied to human skin fibroblasts exposed to the GBH Roundup (GLYP-R). Cytotoxicity, cell death, and oxidative stress assays were performed to evaluate potential damage caused by GLYP-R in fibroblasts. The herbicide showed a cytotoxic effect at concentrations above 100.0 mg L-1, with IC50 = 164.2 ± 8.7 mg L-1, inducing significant reactive oxygen species (ROS) production and necrosis. A GC×GC/Q-TOFMS method using derivatization with propyl chloroformate/propanol was developed for untargeted analysis, allowing the identification of 400 metabolites of different classes in the samples. The most significant compounds in the discrimination and classification of the samples were fatty acids and amino acids (AA). Based on the relevance of AA in untargeted analysis, a targeted analysis of 21 AA was performed using the same validated GC×GC method. Metabolomic analyses allowed the construction of two biomarker models with performance evaluated by receiver operating characteristic (ROC) curves: an untargeted model formed by four metabolites (methylcysteine, N-acetyl-l-methionine, methyl stearate, and linoleic acid) and a targeted model formed by three AA (l-glutamic acid, l-cysteine, and γ-aminobutyric acid). This study is the first to report the use of metabolomics to evaluate human skin cells exposed to GLYP-R, contributing to the toxicological research on glyphosate.

A Protocol for GC-MS Profiling of Chiral Secondary Amino Acids

A simple analytical workflow is described for gas chromatographic-mass spectrometric (GC-MS)-based chiral profiling of secondary amino acids (AAs) in biological matrices. The sample preparation is carried out directly in aqueous biological sample extracts and involves in situ heptafluorobutyl chloroformate (HFBCF) derivatization-liquid-liquid microextraction of nonpolar products into hexane phase followed by subsequent formation of the corresponding methylamides from the HFB esters by direct treatment with methylamine reagent solution. The (O, N) HFB-butoxycarbonyl-methylamide AA products (HFBOC-MA) are separated on a Chirasil-L-Val capillary column and quantitatively measured by GC-MS operated in selected ion monitoring (SIM) mode. The protocol includes 12 simple pipetting steps and covers the quantitative analysis of 8 L, D pairs of secondary amino acids, including proline, isomeric 3-, 4-hydroxyprolines, pipecolic acid, nipecotic acid, azetidine-2-carboxylic acid, and cis- and trans-5-hydroxy-L-pipecolic acid using 13C5 -L-proline as an internal standard. The individual analytical steps are commented on and explained, with emphasis on the chiral GC-MS analysis of secondary amino acids in human urine, serum, and peptide hydrolysate samples.

An easy and sensitive assay for acetohydroxyacid synthases based on the simultaneous detection of substrates and products in a single step

Acetohydroxyacid synthase (AHAS, EC 2.2.1.6) catalyzes the first step in the synthesis of the branched-chain amino acids valine, leucine, and isoleucine, pathways being present in plants and microorganisms, but not in animals. Thus, AHAS is an important target for numerous herbicides and, more recently, for the development of antimicrobial agents. The need to develop new and optimized herbicides and pharmaceuticals requires a detailed understanding of the biochemistry of AHAS. AHAS transfers an activated two-carbon moiety derived from pyruvate to either pyruvate or 2-oxobutyrate as acceptor substrates, forming 2-acetolactate or 2-acetohydroxy-2-butyrate, respectively. Various methods have been described in the literature to biochemically characterize AHAS with respect to substrate preferences, substrate specificity, or kinetic parameters. However, the simultaneous detection and quantification of substrates and unstable products of the AHAS-catalyzed reaction have always been a challenge. Using AHAS isoform II from Escherichia coli, we have developed a sensitive assay for AHAS-catalyzed reactions that uses derivatization with ethyl chloroformate to stabilize and volatilize all reactants in the aqueous solution and detect them by gas chromatography coupled to flame ionization detection or mass spectrometry. This assay allows us to characterize the product formation in reactions in single and dual substrate reactions and the substrate specificity of AHAS, and to reinterpret previous biochemical observations. This assay is not limited to the AHAS-catalyzed reactions, but should be applicable to studies of many metabolic pathways.

Comparative characterization of the infant gut microbiome and their maternal lineage by a multi-omics approach

The human gut microbiome establishes and matures during infancy, and dysregulation at this stage may lead to pathologies later in life. We conducted a multi-omics study comprising three generations of family members to investigate the early development of the gut microbiota. Fecal samples from 200 individuals, including infants (0-12 months old; 55% females, 45% males) and their respective mothers and grandmothers, were analyzed using two independent metabolomics platforms and metagenomics. For metabolomics, gas chromatography and capillary electrophoresis coupled to mass spectrometry were applied. For metagenomics, both 16S rRNA gene and shotgun sequencing were performed. Here we show that infants greatly vary from their elders in fecal microbiota populations, function, and metabolome. Infants have a less diverse microbiota than adults and present differences in several metabolite classes, such as short- and branched-chain fatty acids, which are associated with shifts in bacterial populations. These findings provide innovative biochemical insights into the shaping of the gut microbiome within the same generational line that could be beneficial in improving childhood health outcomes.

Structural elucidation of derivatives of polyfunctional metabolites after methyl chloroformate derivatization by high-resolution mass spectrometry gas chromatography. Application to microbiota metabolites

Metabolomics has become an essential discipline in the study of microbiome, emerging gas chromatography coupled to mass spectrometry as the most mature, robust, and reproducible analytical technique. Silylation is the most widely used chemical derivatization strategy, although it has some limitations. In this regard, alkylation by alkyl chloroformate offers some advantages, such as a rapid reaction, milder conditions, better reproducibility, and the generation of more stable derivatives. However, commercial spectral libraries do not include many of the alkyl derivatives, mainly for polyfunctional metabolites, which can form multiple derivatives. That introduces a huge bias in untargeted metabolomics leading to common errors such as duplicates, unknowns, misidentifications, wrong assignations, and incomplete results from which non-reliable findings and conclusions will be retrieved. For this reason, the purpose of this study is to overcome these shortcomings and to expand the knowledge of metabolites in general and especially those closely related to the gut microbiota through the thorough study of the reactivity of the different functional groups in real matrix derivatized by methyl chloroformate, a common representative alkylation reagent. To this end, a systematic workflow has been developed based on exhaustive structural elucidation, along with computational simulation, and taking advantage of the high sensitivity and high-resolution gas chromatography-mass spectrometry. Several empirical rules have been established according to chemically different entities (free fatty acids, amino acids, polyols, sugars, amines, and polyfunctional groups, etc.) to predict the number of derivatives formed from a single metabolite, as well as their elution order and structure. In this work, some methyl chloroformate derivatives not previously reported as well as the mechanisms to explain them are given. Extremely important is the interconversion of E- and Z- geometric isomers of unsaturated dicarboxylic acids (case of fumaric-maleic and case of citraconic-mesaconic acids), or the formation of cycled derivatives for amino acids, as well as common metabolites, as in the case of serine and cysteine, and many others.

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.

Evaluation of amino acid profile by targeted metabolomics in the eukaryotic model under exposure of benzo[a]pyrene as the exclusive stressor

Amino acids (AAs) are a class of important metabolites in metabolomics methodology that investigates metabolite changes in a cell, tissue, or organism for early diagnosis of diseases. Benzo[a]pyrene (BaP) is considered a priority contaminant by different environmental control agencies because it is a proven carcinogenic compound for humans. Therefore, it is important to evaluate the BaP interference in the metabolism of amino acids. In this work, a new amino acid extraction procedure (derivatized with propyl chloroformate/propanol) using functionalized magnetic carbon nanotubes was developed and optimized. A hybrid nanotube was used followed by desorption without heating, and excellent extraction of analytes was obtained. After exposure of Saccharomyces cerevisiae, the BaP concentration of 25.0 μmol L-1 caused changes in cell viability, indicating metabolic changes. A fast and efficient GC/MS method using a Phenomenex ZB-AAA column was optimized, enabling the determination of 16 AAs in yeasts exposed or not to BaP. A comparison of AA concentrations obtained in the two experimental groups showed that glycine (Gly), serine (Ser), phenylalanine (Phe), proline (Pro), asparagine (Asn), aspartic acid (Asp), glutamic acid (Glu), tyrosine (Tyr), and leucine (Leu) statistically differentiated, after subsequent application of ANOVA with Bonferroni post-hoc test, with a confidence level of 95%. This amino acid pathway analysis confirmed previous studies that revealed the potential of these AAs as toxicity biomarker candidates.

Degumming and characterization of Bombyx mori and non-mulberry silks from Saturniidae silkworms

In this study, cocoons and degummed silk samples of Bombyx mori and twenty Saturniidae species of the genera Actias, Attacus, Argema, Antheraea, Caligula, Callosamia, Cricula, Epiphora, Hyalophora, Loepa, Samia and Saturnia are studied to gain an insight into their morphology, chemical composition and physical structure. For this purpose, silk samples are characterized by optical microscopy and FTIR spectroscopy in attenuated total reflection mode (ATR-FTIR spectroscopy). Furthermore, degummed silk samples are analyzed for their amino acid (AA) composition by GC-FID. In the course of method development, various degumming methods are tested using alkalis, citric acid, enzymes and detergents. A mixture of 0.1% sodium carbonate and 2.5% ethylenediamine proves to be an effective agent for degumming Saturniidae and B. mori cocoons. After hydrolysis of the fibroin filaments with 6 N hydrochloric acid and derivatization with propyl chloroformate, fifteen AAs are identified and qualified. This method shows a satisfactory overall analytical performance with an average recovery rate of 95% at the medium concentration level. The chemical composition of the different silks was considered comparatively. Within a genus, the analyses usually show a high degree of similarity in AA composition and the resulting structural indices, whereas differences are found between genera.

A protocol based on solid phase microextraction -gas chromatography-tandem mass spectrometry for the monitoring of parabens and bisphenols in human saliva

The herein presented work aims to the development of an easy method for the quantitative determination of parabens and bisphenols in human salivabased on the use of methyl chloroformate as a derivatizing agent, followed by solid-phase microextraction (SPME) and gas chromatography-triple quadrupole mass spectrometry (GC-QqQ-MS) analysis with selected reaction monitoring (SRM). Using multivariate analysis, two derivatization strategies were compared and optimized, demonstrating that the use of methyl chloroformate led to better sensitivity than the classical derivatization by acetic anhydride. Good performance in the sorption process of the derivatized target analytes was obtained using the most recent commercialized overcoated fiber (PDMS/DVB/PDMS). The validation procedure of the final protocol led to satisfactory results in terms of linearity, limit of quantitation, accuracy, and precision. All parabens were quantified from 10 ng/L using the developed method, except for methylparaben, which was quantified from 100 ng/L along with all bisphenols. Intra- and inter-day accuracy and intra- and inter-day precision can be considered satisfactory for all analytes (values between 73% and 118%), except for the inter-day accuracy of BPF. Quite good results also in terms of matrix effect were obtained for the target compounds (range 71% to 118%, RSD% less than 13.6%), except for BPA at the middle concentration and MeP at the lowest concentration. The greenness of the method was evaluated and the results indicated that our approach is more eco-friendly than previously published methods. Based on its characteristics, the presented method can be considered a suitable approach to determine parabens and bisphenols in routine analysis for biomonitoring purposes.

Rapid and Simultaneous Determination of Free Aromatic Carboxylic Acids and Phenols in Commercial Juices by GC-MS after Ethyl Chloroformate Derivatization

Natural phenol and phenolic acids are widely distributed in the plant kingdom and the major dietary sources include fruits and beverages derived therefrom. Over the past decades, these compounds have been widely investigated for their beneficial effects on human health and, at the same time, several analytical methods have been developed for their determination in these matrices. In the present paper, 19 different aromatic carboxylic acids and phenols were characterized by GC-MS using ethyl chloroformate as the derivatizing agent. This procedure occurs quickly at room temperature and takes place in aqueous media simultaneously with the extraction step in the presence of ethanol using pyridine as a catalyst. The analytical method herein developed and validated presents excellent linearity in a wide concentration range (25–3000 ng/mL), low LOQ (in the range 25–100 ng/mL) and LOD (in the range 12.5–50 ng/mL), and good accuracy and precision. As a proof of concept, ethyl chloroformate derivatization was successfully applied to the analysis of a selection of commercial fruit juices (berries, grape, apple, pomegranate) particularly rich in phenolic compounds. Some of these juices are made up of a single fruit, whereas others are blends of several fruits. Our results show that among the juices analyzed, those containing cranberry have a total concentration of the free aromatic carboxylic acids and phenols tested up to 15 times higher than other juices.

Defining Blood Plasma and Serum Metabolome by GC-MS

Metabolomics uses advanced analytical chemistry methods to analyze metabolites in biological samples. The most intensively studied samples are blood and its liquid components: plasma and serum. Armed with advanced equipment and progressive software solutions, the scientific community has shown that small molecules’ roles in living systems are not limited to traditional “building blocks” or “just fuel” for cellular energy. As a result, the conclusions based on studying the metabolome are finding practical reflection in molecular medicine and a better understanding of fundamental biochemical processes in living systems. This review is not a detailed protocol of metabolomic analysis. However, it should support the reader with information about the achievements in the whole process of metabolic exploration of human plasma and serum using mass spectrometry combined with gas chromatography.

Mechanism of Alkyl Chloroformate-Mediated Esterification of Carboxylic Acids in Aqueous Media

The protection of carboxyl groups by esterification has been the most common method in macroscale and microscale chemistries. The esterification is usually conducted under anhydrous conditions; however, in biological chemistry and related fields, the reaction is of major concern in aqueous environments. Immediate esterification of the carboxyl in aqueous alcoholic media driven by an alkyl chloroformate and pyridine has been such a method which has found widespread use in many research and industrial laboratories. Nevertheless, the reaction mechanism has not yet been investigated, to our knowledge, and is not well understood. Herein, we describe the reaction intermediates and demonstrate that the reaction proceeds via a continual formation of the N-acylpyridinium intermediate decomposed by several reaction channels to the final ester. The understanding of the mechanism could encourage novel laboratory applications of this important esterification method.

Combined in vivo muscle mass, muscle protein synthesis and muscle protein breakdown measurement: a 'Combined Oral Stable Isotope Assessment of Muscle (COSIAM)' approach

Optimising approaches for measuring skeletal muscle mass and turnover that are widely applicable, minimally invasive and cost effective is crucial in furthering research into sarcopenia and cachexia. Traditional approaches for measurement of muscle protein turnover require infusion of expensive, sterile, isotopically labelled tracers which limits the applicability of these approaches in certain populations (e.g. clinical, frail elderly). To concurrently quantify skeletal muscle mass and muscle protein turnover i.e. muscle protein synthesis (MPS) and muscle protein breakdown (MPB), in elderly human volunteers using stable-isotope labelled tracers i.e. Methyl-[D₃]-creatine (D₃-Cr), deuterium oxide (D₂O), and Methyl-[D₃]-3-methylhistidine (D₃-3MH), to measure muscle mass, MPS and MPB, respectively. We recruited 10 older males (71 ± 4 y, BMI: 25 ± 4 kg^.m², mean ± SD) into a 4-day study, with DXA and consumption of D₂O and D₃-Cr tracers on day 1. D₃-3MH was consumed on day 3, 24 h prior to returning to the lab. From urine, saliva and blood samples, and a single muscle biopsy (vastus lateralis), we determined muscle mass, MPS and MPB. D₃-Cr derived muscle mass was positively correlated to appendicular fat-free mass (AFFM) estimated by DXA (r = 0.69, P = 0.027). Rates of cumulative myofibrillar MPS over 3 days were 0.072%/h (95% CI, 0.064 to 0.081%/h). Whole-body MPB over 6 h was 0.052 (95% CI, 0.038 to 0.067). These rates were similar to previous literature. We demonstrate the potential for D₃-Cr to be used alongside D₂O and D₃-3MH for concurrent measurement of muscle mass, MPS, and MPB using a minimally invasive design, applicable for clinical and frail populations.

Simultaneous quantification of eleven short-chain fatty acids by derivatization and solid phase microextraction - Gas chromatography tandem mass spectrometry

As metabolites of the gut microbiome, short-chain fatty acids (SCFAs) played an important role in the diagnosis of the metabolic diseases. Because of the high polarity, high volatility and complex matrix of biological samples, the highly sensitive, selective and accurate method to determine SCFAs remains a major challenge. Herein, a new method for simultaneous quantification of eleven SCFAs by derivatization combined with solid phase microextraction (SPME) and gas chromatography tandem mass spectrometry (GC-MS/MS) was developed. Isobutyl chloroformate coupled with isobutanol was used as the reaction reagent to derivatize SCFAs. The method validation data showed a satisfactory linearity with the linear regression coefficients (R) ranging from 0.9964 to 0.9996. The limit of detection (LOD) of all SCFAs ranges from 0.01 ng·mL^-1 to 0.72 ng·mL^-1 and the limit of quantification (LOQ) ranges from 0.04 ng·mL^-1 to 2.41 ng·mL^-1. The intra-day and inter-day precision (RSDs) ranged from 0.65% to 8.92% and 1.62% to 15.61%, respectively. The recovery ranged from 88.10% to 108.71%. Finally, the developed method was successfully used to determine SCFAs in mice fecal sample, and ten of the SCFAs were found in feces of mice, including formic acid.

Amino Acids, Peptides, and Proteins: Implications for Nanotechnological Applications in Biosensing and Drug/Gene Delivery

Over various scientific fields in biochemistry, amino acids have been highlighted in research works. Protein, peptide- and amino acid-based drug delivery systems have proficiently transformed nanotechnology via immense flexibility in their features for attaching various drug molecules and biodegradable polymers. In this regard, novel nanostructures including carbon nanotubes, electrospun carbon nanofibers, gold nanoislands, and metal-based nanoparticles have been introduced as nanosensors for accurate detection of these organic compounds. These nanostructures can bind the biological receptor to the sensor surface and increase the surface area of the working electrode, significantly enhancing the biosensor performance. Interestingly, protein-based nanocarriers have also emerged as useful drug and gene delivery platforms. This is important since, despite recent advancements, there are still biological barriers and other obstacles limiting gene and drug delivery efficacy. Currently available strategies for gene therapy are not cost-effective, and they do not deliver the genetic cargo effectively to target sites. With rapid advancements in nanotechnology, novel gene delivery systems are introduced as nonviral vectors such as protein, peptide, and amino acid-based nanostructures. These nano-based delivery platforms can be tailored into functional transformation using proteins and peptides ligands based nanocarriers, usually overexpressed in the specified diseases. The purpose of this review is to shed light on traditional and nanotechnology-based methods to detect amino acids, peptides, and proteins. Furthermore, new insights into the potential of amino protein-based nanoassemblies for targeted drug delivery or gene transfer are presented.

Chemical Conversion of Hardly Ionizable Rhenium Aryl Chlorocomplexes with p-Substituted Anilines

Fast and selective analytical methods help to ensure the chemical identity and desired purity of the prepared complexes before their medical application, and play an indispensable role in clinical practice. Mass spectrometry, despite some limitations, is an integral part of these methods. In the context of mass spectrometry, specific problems arise with the low ionization efficiency of particular analytes. Chemical derivatization was used as one of the most effective methods to improve the analyte's response and separation characteristics. The Schotten-Baumann reaction was successfully adapted for the derivatization of ESI hardly ionizable Re(VII) bis(catechol) oxochlorocomplex. Various alkyl and halogen p-substituted anilines as possible derivatization agents were tested. Unlike the starting complex, the reaction products were easily ionizable in electrospray, providing structurally characteristic molecular and fragment anions. DFT computer modeling, which proposed significant conformation changes of prepared complexes within their deprotonation, proved to have a close link to MS spectra. High-resolution MS and MS/MS measurements complemented with collision-induced dissociation experiments for detailed specification of prepared complexes' fragmentation pathways were used. The specified fragmentation schemes were analogous for all studied derivatives, with an exception for [Re(O)(Cat)2PIPA].

Effect of rumen-protected lysine supplementation of diets based on corn protein fed to lactating dairy cows

This trial tested whether rumen-protected Lys (RPL) supplementation would improve the nutritive value of rumen-undegradable protein (RUP) from corn protein. Thirty-two lactating Holstein cows were blocked by days in milk and parity into 8 squares of 4 cows each in replicated 4 × 4 Latin squares. Treatments provided all supplemental crude protein from: (1) soy protein (67% expeller soybean meal plus 33% solvent soybean meal); (2) a blend of soy and corn protein (33% expeller soybean meal, 17% solvent soybean meal, 25% corn gluten meal plus 25% distillers dried grains with solubles); (3) corn protein (50% corn gluten meal plus 50% distillers dried grains with solubles); or (4) corn protein plus RPL [diet 3 top-dressed with RPL (125 g/d of AjiPro-L Generation 1, supplying an estimated 20 g of absorbable Lys/d)]. Diets contained (dry matter basis) 22% alfalfa silage, 43% corn silage, 18% ground high-moisture and dry corn, 2.4% mineral-vitamin premix, 1.5 to 3.9% soy hulls, 15% crude protein, 30 to 32% neutral detergent fiber and predicted to contain equal rumen-degradable protein, RUP, and metabolizable protein. Cows within squares were randomly assigned to treatment sequences and fed diets for 4-wk periods before switching; production data and blood samples were collected during last 2 wk of each period. Data were analyzed using the mixed procedures of SAS. Intake was highest on diet 1, intermediate on diets 2 and 3, and lowest on diet 4; body weight gain was highest on diet 3, intermediate on diets 1 and 2 and lowest on diet 4. Intakes and body weight changes were reflected by differences in milk/dry matter intake, which was highest on diets 2 and 4 and lowest on diet 3. Milk yield was lower on diet 3 (44.3 kg/d) than on diets 1, 2, and 4 (average 45.8 kg/d) and protein yield was highest on diets 1 and 2 (average 1.35 kg/d), intermediate on diet 4 (1.30 kg/d), and lowest on diet 3 (1.25 kg/d). No effects of diet were detected on ruminal metabolites. Free nonessential amino acids and total protein AA were elevated in blood plasma on diet 3, reflecting reduced utilization for milk protein synthesis. These results indicated that 50% dilution of soybean meal RUP with that from corn protein did not reduce yield and that supplementing RPL to the corn protein-based diet increased yield 1.1 kg of milk/d and 50 g of true protein/d.

Ethylchloroformate Derivatization for GC-MS Analysis of Resveratrol Isomers in Red Wine

Resveratrol (3,5,4′-trihydroxystilbene) is a natural compound that can be found in high concentrations in red wine and in many typical foods found in human diet. Over the past decades, resveratrol has been widely investigated for its potential beneficial effects on human health. At the same time, numerous analytical methods have been developed for the quantitative determination of resveratrol isomers in oenological and food matrices. In the present work, we developed a very fast and sensitive GC–MS method for the determination of resveratrol in red wine based on ethylchloroformate derivatization. Since this reaction occurs directly in the water phase during the extraction process itself, it has the advantage of significantly reducing the overall processing time for the sample. This method presents low limits of quantification (LOQ) (25 ng/mL and 50 ng/mL for cis- and trans-resveratrol, respectively) and excellent accuracy and precision. Ethylchloroformate derivatization was successfully applied to the analysis of resveratrol isomers in a selection of 15 commercial Italian red wines, providing concentration values comparable to those reported in other studies. As this method can be easily extended to other classes of molecules present in red wine, it allows further development of new GC–MS methods for the molecular profiling of oenological matrices.

A rapid method for the quantification of urinary phthalate monoesters: A new strategy for the assessment of the exposure to phthalate ester by solid-phase microextraction with gas chromatography and tandem mass spectrometry

In the following work, a new method for the analysis of the phthalate monoesters in human urine was reported. Phthalate monoesters are metabolites generated as a result of phthalate exposure. In compliance with the dictates of Green Analytical Chemistry, a rapid and simple protocol was developed and optimized for the quantification of phthalate monoesters (i.e., monoethyl phthalate, monoisobutyl phthalate, mono-n-butyl phthalate, mono-(2-ethylhexyl) phthalate, mono-n-octyl phthalate, monocyclohexyl phthalate, mono-isononyl phthalate) in human urine, which entails preceding derivatization with methyl chloroformate combined with the use of commercial solid phase microextraction and the analysis by gas chromatography-triple quadrupole mass spectrometry. The affinity of the derivatized analytes toward five commercial coatings was evaluated, and in terms of analyte extraction, the best results were reached with the use of the divinylbenzene/carboxen/polydimethylsiloxane fiber. The multivariate approach of experimental design was used to seek for the best working conditions of the derivatization reaction and the solid phase microextraction, thus obtaining the optimum response values. The proposed method was validated according to the guidelines issued by the Food and Drug Administration achieving satisfactory values in terms of linearity, sensitivity, matrix effect, intra- and inter-day accuracy, and precision.

Development and Validation of a New Gas Chromatography-Tandem Mass Spectrometry Method for the Measurement of Enrichment of Glyoxylate Metabolism Analytes in Hyperoxaluria Patients Using a Stable Isotope Procedure

Primary hyperoxalurias (PH) are inborn errors of glyoxylate metabolism characterized by an increase in endogenous oxalate production. Oxalate overproduction may cause calcium-oxalate crystal formation leading to kidney stones, nephrocalcinosis, and ultimately kidney failure. Twenty-four hour urine oxalate excretion is an inaccurate measure for endogenous oxalate production in PH patients and not applicable in those with kidney failure. Treatment efficacy cannot be assessed with this measure during clinical trials. We describe the development and validation of a gas chromatography–tandem mass spectrometry method to analyze the samples obtained following a stable isotope infusion protocol of ¹³C₂-oxalate and 1-¹³C-glycolate in both healthy individuals and PH patients. Isotopic enrichments of plasma oxalate, glycolate, and glyoxylate were measured on a gas chromatography–triple quadrupole mass spectrometry system using ethylhydroxylamine and N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) for analyte derivatization. Method precision was good for oxalate and glycolate (coefficients of variation [CV] were <6.3% and <4.2% for inter- and intraday precision, respectively) and acceptable for glyoxylate (CV <18.3% and <6.7% for inter- and intraday precision, respectively). The enrichment curves were linear over the specified range. Sensitivity was sufficient to accurately analyze enrichments. This new method allowed calculation of kinetic features of these metabolites, thus enabling a detailed analysis of the various pathways involved in glyoxylate metabolism. The method will further enhance the investigation of the metabolic PH derangements, provides a tool to accurately assess the therapeutic efficacy of new promising therapeutic interventions for PH, and could serve as a clinical tool to improve personalized therapeutic strategies.

Adenine-functionalized polypropylene glycol: A novel stationary phase for gas chromatography offering good inertness for acids and bases combined with a unique selectivity

This work presents the investigation of utilizing adenine-functionalized polypropylene glycol (APPG) for capillary gas chromatographic separations. The statically coated APPG column (0.25 mm i.d.) showed moderate polarity and high column efficiencies of 4660 plates/m and 4376 plates/m determined by n-octanol and naphthalene, respectively. Remarkably, the APPG column baseline resolved all the components of the Grob test mixture and displayed good peak shapes for some stringent analytes that are prone to peak tailing or severe adsorption. Also, it achieved complete separation of dimethylaniline isomers, which are difficult to be resolved due to their high resemblance in structures and properties. The above results demonstrate the high selectivity and inertness of the APPG column and its distinct advantages over the polypropylene glycol (PPG) column and commercial polyethylene glycol (PEG) column. In addition, its separation performance has good repeatability with the RSD values on retention times below 0.05% for run-to-run, 0.11-0.12% for day-to-day and 1.7-1.9% for column-to-column, respectively. Further, the APPG column was applied to determination of isomer impurities in commercial dimethylaniline products and to determination of the additives of anilines and phenols in a hair-dye product, proving its great potential for practical GC analysis.

Pivotal role of inter-organ aspartate metabolism for treatment of mitochondrial aspartate-glutamate carrier 2 (citrin) deficiency, based on the mouse model

Previous studies using citrin/mitochondrial glycerol-3-phosphate (G3P) dehydrogenase (mGPD) double-knockout mice have demonstrated that increased dietary protein reduces the extent of carbohydrate-induced hyperammonemia observed in these mice. This study aimed to further elucidate the mechanisms of this effect. Specific amino acids were initially found to decrease hepatic G3P, or increase aspartate or citrulline levels, in mGPD-knockout mice administered ethanol. Unexpectedly, oral glycine increased ammonia in addition to lowering G3P and increasing citrulline. Subsequently, simultaneous glycine-plus-sucrose (Gly + Suc) administration led to a more severe hyperammonemic state in double-KO mice compared to sucrose alone. Oral arginine, ornithine, aspartate, alanine, glutamate and medium-chain triglycerides all lowered blood ammonia following Gly + Suc administration, with combinations of ornithine-plus-aspartate (Orn + Asp) or ornithine-plus-alanine (Orn + Ala) suppressing levels similar to wild-type. Liver perfusion and portal vein-arterial amino acid differences suggest that oral aspartate, similar to alanine, likely activated ureagenesis from ammonia and lowered the cytosolic NADH/NAD⁺ ratio through conversion to alanine in the small intestine. In conclusion, Gly + Suc administration induces a more severe hyperammonemic state in double-KO mice that Orn + Asp or Orn + Ala both effectively suppress. Aspartate-to-alanine conversion in the small intestine allows for effective oral administration of either, demonstrating a pivotal role of inter-organ aspartate metabolism for the treatment of citrin deficiency.

Amino Acid Analysis in Physiological Samples by GC-MS with Propyl Chloroformate Derivatization and iTRAQ-LC-MS/MS

Two mass spectrometry-based methods for the quantitative analysis of free amino acids are described. The first method uses propyl chloroformate/propanol derivatization and gas chromatography-quadrupole mass spectrometry (GC-qMS) analysis in a single-ion monitoring mode. Derivatization is carried out directly in the aqueous samples, thereby allowing automation of the entire procedure, including addition of reagents, extraction, and injection into the GC-MS. The method delivers the quantification of 26 amino acids. The iTRAQ method employs the labeling of amino acids with isobaric iTRAQ tags. The tags contain two different cleavable reporter ions, one for the sample and one for the standard, which are detected by fragmentation in a tandem mass spectrometer (MS/MS). Reversed-phase liquid chromatography (RP-LC) of the labeled amino acids is performed prior to mass spectrometric analysis to separate isobaric amino acids. The commercial iTRAQ kit allows for the analysis of 42 physiological amino acids with a respective isotope-labeled standard for each of these 42 amino acids.

Acid monomer analysis in waterborne polymer systems by targeted labeling of carboxylic acid functionality, followed by pyrolysis - gas chromatography

Pyrolysis - gas chromatography - (PyGC) is a common method to analyse the composition of natural and synthetic resins. The analysis of acid functionality in, for example, waterborne polyacrylates and polyurethanes polymers has proven to be difficult due to solubility issues, inter- and intramolecular interaction effects, lack of detectability in chromatographic analysis, and lack of thermal stability. Conventional analytical techniques, such as PyGC, cannot be used for the direct detection and identification of acidic monomers, due to thermal rearrangements that take place during pyrolysis. To circumvent this, the carboxylic acid groups are protected prior to thermal treatment by reaction with 2-bromoacetophenone. Reaction conditions are investigated and optimised wrt. conversion measurements. The aproach is applied to waterborne polyacryalates and the results are discussed. This approach enables identification and (semi)quantitative analysis of different acid functionalities in waterborne polymers by PyGC.

A novel fast method for aqueous derivatization of THC, OH-THC and THC-COOH in human whole blood and urine samples for routine forensic analyses

A novel aqueous in situ derivatization procedure with propyl chloroformate (PCF) for the simultaneous, quantitative analysis of Δ⁹ -tetrahydrocannabinol (THC), 11-hydroxy-Δ⁹ -tetrahydrocannabinol (OH-THC) and 11-nor-Δ⁹ -tetrahydrocannabinol-carboxylic acid (THC-COOH) in human blood and urine is proposed. Unlike current methods based on the silylating agent [N,O-bis(trimethylsilyl)trifluoroacetamide] added in an anhydrous environment, this new proposed method allows the addition of the derivatizing agent (propyl chloroformate, PCF) directly to the deproteinized blood and recovery of the derivatives by liquid-liquid extraction. This novel method can be also used for hydrolyzed urine samples. It is faster than the traditional method involving a derivatization with trimethyloxonium tetrafluoroborate. The analytes are separated, detected and quantified by gas chromatography-mass spectrometry in selected ion monitoring mode (SIM). The method was validated in terms of selectivity, capacity of identification, limits of detection (LOD) and quantification (LOQ), carryover, linearity, intra-assay precision, inter-assay precision and accuracy. The LOD and LOQ in hydrolyzed urine were 0.5 and 1.3 ng/mL for THC and 1.2 and 2.6 ng/mL for THC-COOH, respectively. In blood, the LOD and LOQ were 0.2 and 0.5 ng/mL for THC, 0.2 and 0.6 ng/mL for OH-THC, and 0.9 and 2.4 ng/mL for THC-COOH, respectively. This method was applied to 35 urine samples and 50 blood samples resulting to be equivalent to the previously used ones with the advantage of a simpler method and faster sample processing time. We believe that this method will be a more convenient option for the routine analysis of cannabinoids in toxicological and forensic laboratories.

Metabolomics: A High-Throughput Platform for Metabolite Profile Exploration

Metabolomics aims to quantitatively measure small-molecule metabolites in biological samples, such as bodily fluids (e.g., urine, blood, and saliva), tissues, and breathe exhalation, which reflects metabolic responses of a living system to pathophysiological stimuli or genetic modification. In the past decade, metabolomics has made notable progresses in providing useful systematic insights into the underlying mechanisms and offering potential biomarkers of many diseases. Metabolomics is a complementary manner of genomics and transcriptomics, and bridges the gap between genotype and phenotype, which reflects the functional output of a biological system interplaying with environmental factors. Recently, the technology of metabolomics study has been developed quickly. This review will discuss the whole pipeline of metabolomics study, including experimental design, sample collection and preparation, sample detection and data analysis, as well as mechanism interpretation, which can help understand metabolic effects and metabolite function for living organism in system level.

Comparative evaluation of three different ELISA assays and HPLC-ESI-ITMS/MS for the analysis of Nε-carboxymethyl lysine in food samples

N^ε-carboxymethyl-lysine (CML) is measured in food, but there is a controversy concerning the most convenient yet reliable method(s) for this task. This work compares three different ELISA assays and HPLC-ESI-ITMS/MS for the analysis of CML in several food items. The four methods showed the same decreasing order of CML concentration: beef, bacon>chicken > fish>dairy products>grain products>fruits/vegetables. HPLC-ESI-ITMS/MS results highly correlated with those obtained by ELISA performed with monoclonal CML-antibody (β=0.98, p<0.0001) whereas My Bio Source® kit results were not correlated with those provided by Lamider®. Small differences of CML concentrations in food items prepared by different culinary treatment were clearly distinguished by HPLC-ESI-ITMS/MS, but could not always be detected by ELISA. This work demonstrates a reasonable relationship between CM determined by ELISA and HPLC-ESI-ITMS/MS and therefore supports the implementation of ELISA in food CML/AGEs screening.

High Throughput and Quantitative Measurement of Microbial Metabolome by Gas Chromatography/Mass Spectrometry Using Automated Alkyl Chloroformate Derivatization

The ability to identify and quantify small molecule metabolites derived from gut microbial-mammalian cometabolism is essential for the understanding of the distinct metabolic functions of the microbiome. To date, analytical protocols that quantitatively measure a complete panel of microbial metabolites in biological samples have not been established but are urgently needed by the microbiome research community. Here, we report an automated high-throughput quantitative method using a gas chromatography/time-of-flight mass spectrometry (GC/TOFMS) platform to simultaneously measure over one hundred microbial metabolites in human serum, urine, feces, and Escherichia coli cell samples within 15 min per sample. A reference library was developed consisting of 145 methyl and ethyl chloroformate (MCF and ECF) derivatized compounds with their mass spectral and retention index information for metabolite identification. These compounds encompass different chemical classes including fatty acids, amino acids, carboxylic acids, hydroxylic acids, and phenolic acids as well as benzoyl and phenyl derivatives, indoles, etc., that are involved in a number of important metabolic pathways. Within an optimized range of concentrations and sample volumes, most derivatives of both reference standards and endogenous metabolites in biological samples exhibited satisfactory linearity (R2 > 0.99), good intrabatch reproducibility, and acceptable stability within 6 days (RSD < 20%). This method was further validated by examination of the analytical variability of 76 paired human serum, urine, and fecal samples as well as quality control samples. Our method involved using high-throughput sample preparation, measurement with automated derivatization, and rapid GC/TOFMS analysis. Both techniques are well suited for microbiome metabolomics studies.

Oral aversion to dietary sugar, ethanol and glycerol correlates with alterations in specific hepatic metabolites in a mouse model of human citrin deficiency

Mice carrying simultaneous homozygous mutations in the genes encoding citrin, the mitochondrial aspartate-glutamate carrier 2 (AGC2) protein, and mitochondrial glycerol-3-phosphate dehydrogenase (mGPD), are a phenotypically representative model of human citrin (a.k.a., AGC2) deficiency. In this study, we investigated the voluntary oral intake and preference for sucrose, glycerol or ethanol solutions by wild-type, citrin (Ctrn)-knockout (KO), mGPD-KO, and Ctrn/mGPD double-KO mice; all substances that are known or suspected precipitating factors in the pathogenesis of human citrin deficiency. The double-KO mice showed clear suppressed intake of sucrose, consuming less with progressively higher concentrations compared to the other mice. Similar observations were made when glycerol or ethanol were given. The preference of Ctrn-KO and mGPD-KO mice varied with the different treatments; essentially no differences were observed for sucrose, while an intermediate intake or similar to that of the double-KO mice was observed for glycerol and ethanol. We next examined the hepatic glycerol 3-phosphate, citrate, citrulline, lysine, glutamate and adenine nucleotide levels following forced enteral administration of these solutions. A strong correlation between the simultaneous increased hepatic glycerol 3-phosphate and decreased ATP or total adenine nucleotide content and observed aversion of the mice during evaluation of their voluntary preferences was found. Overall, our results suggest that the aversion observed in the double-KO mice to these solutions is initiated and/or mediated by hepatic metabolic perturbations, resulting in a behavioral response to increased hepatic cytosolic NADH and a decreased cellular adenine nucleotide pool. These findings may underlie the dietary predilections observed in human citrin deficient patients.

Metabolomics, Nutrition, and Potential Biomarkers of Food Quality, Intake, and Health Status

Diet, dietary patterns, and other environmental factors such as exposure to toxins are playing an important role in the prevention/development of many diseases, like obesity, type 2 diabetes, and consequently on the health status of individuals. A major challenge nowadays is to identify novel biomarkers to detect as early as possible metabolic dysfunction and to predict evolution of health status in order to refine nutritional advices to specific population groups. Omics technologies such as genomics, transcriptomics, proteomics, and metabolomics coupled with statistical and bioinformatics tools have already shown great potential in this research field even if so far only few biomarkers have been validated. For the past two decades, important analytical techniques have been developed to detect as many metabolites as possible in human biofluids such as urine, blood, and saliva. In the field of food science and nutrition, many studies have been carried out for food authenticity, quality, and safety, as well as for food processing. Furthermore, metabolomic investigations have been carried out to discover new early biomarkers of metabolic dysfunction and predictive biomarkers of developing pathologies (obesity, metabolic syndrome, type-2 diabetes, etc.). Great emphasis is also placed in the development of methodologies to identify and validate biomarkers of nutrients exposure.

Gabapentin, Pregabalin and Vigabatrin Quantification in Human Serum by GC-MS After Hexyl Chloroformate Derivatization

A simple, sensitive and robust method for simultaneous determination of antiepileptic drugs (gabapentin, pregabalin and vigabatrin) in human serum using GC-MS was developed and validated for clinical toxicology purposes. This method employs an emerging class of derivatization agents - alkyl chloroformates allowing the efficient and rapid derivatization of both the amino and carboxylic groups of the tested antiepileptic drugs within seconds. The derivatization protocol was optimized using the Design of Experiment statistical methodology, and the entire sample preparation requires less than 5 min. Linear calibration curves were obtained in the concentration range from 0.5 to 50.0 mg/L, with adequate accuracy (97.9-109.3%) and precision (<12.1%). The method was successfully applied to quantification of selected γ-aminobutyric acid analogs in the serum of patients in both therapeutic and toxic concentration ranges.

Fast exchange fluxes around the pyruvate node: a leaky cell model to explain the gain and loss of unlabelled and labelled metabolites in a tracer experiment

BACKGROUND

Glucose and glutamine are the two dominant metabolic substrates in cancer cells. In (13)C tracer experiments, however, it is necessary to account for all significant input substrates, as some natural (unlabelled) substrate in the medium, often derived from serum, can be metabolised by cells despite not showing signs of net consumption.

RESULTS

Using [U-(13)C6]-glucose tracers and measuring extracellular metabolite enrichments by GC-MS, we found that pancreatic cells HPDE and PANC-1 secrete lactate, pyruvate, TCA cycle metabolites and non-essential amino acids synthesised from glucose. Focusing our investigations on pyruvate exchange in HEK293 cells, we observed that the four metabolites pools, intracellular and extracellular lactate and pyruvate, had similar (13)C enrichment trajectories. This indicated that these metabolites can mix rapidly. Using a hybrid (13)C-MFA, we followed to show that the lactate exchange flux had increased when extracellular lactate concentration was increased by 10-fold. By allowing rapid exchange fluxes around the pyruvate node, (13)C-MFA revealed that PANC-1 cells cultured in [U-(13)C6]-glucose doubled the conversion of unlabelled substrates to pyruvate when treated with TNF-α.

CONCLUSIONS

The current work established the possibility that a cell's range of significant input substrates may be broader than anticipated. Metabolite exchange can affect intracellular enrichments. In particular, we showed that pyruvate was more strongly connected to lactate than to upstream glycolytic intermediates and that a fast lactate exchange may alter the outcome of flux analyses. Nevertheless, the leaky cell model may be an opportunity in disguise-the ability to continuously monitor metabolism using only the enrichments of extracellular metabolites.

Quantitative Identification of Biogenic Nonextractable Pesticide Residues in Soil by (14)C-Analysis

Quantification of nonextractable residues (NER) of pesticides in soil is feasible by use of radioactively labeled compounds, but structural information on these long-term stabilized residues is usually lacking. Microorganisms incorporate parts of the radiolabeled ((14)C-) carbon from contaminants into microbial biomass, which after cell death enters soil organic matter, thus forming biogenic nonextractable residues (bioNER). The formation of bioNER is not yet determinable in environmental fate studies due to a lack of methodology. This paper focuses on the development of a feasible analytical method to quantify proteinaceous carbon, since proteins make up the largest mass portion of bacterial cells. The test substance (14)C-bromoxynil after 56 days forms more than 70% of NER in soil. For further characterization of NER the amino acids were extracted, purified, and separated by two-dimensional thin-layer chromatography (TLC). Visualization of the (14)C-amino acids was performed by bioimaging, unambiguous identification by GC-MS and LC-MS/MS. Our analysis revealed that after 56 days of incubation about 14.5% of the (14)C-label of bromoxynil was incorporated in amino acids. Extrapolating this content based on the amount of proteins in the biomass (55%), in total about 26% of the NER is accounted for by bioNER and thus is not environmentally relevant.

PCI-GC-MS-MS approach for identification of non-amino organic acid and amino acid profiles

Alkyl chloroformate have been wildly used for the fast derivatization of metabolites with amino and/or carboxyl groups, coupling of powerful separation and detection systems, such as GC-MS, which allows the comprehensive analysis of non-amino organic acids and amino acids. The reagents involving n-alkyl chloroformate and n-alcohol are generally employed for providing symmetric labeling terminal alkyl chain with the same length. Here, we developed an asymmetric labeling strategy and positive chemical ionization gas chromatography-tandem mass spectrometry (PCI-GC-MS-MS) approach for determination of non-amino organic acids and amino acids, as well as the short chain fatty acids. Carboxylic and amino groups could be selectively labelled by propyl and ethyl groups, respectively. The specific neutral loss of C₃H₈O (60Da), C₃H₅O₂ (74Da) and C₄H₈O₂ (88Da) were useful in the selective identification for qualitative analysis of organic acids and amino acid derivatives. PCI-GC-MS-MS using multiple reaction monitoring (MRM) was applied for semi-quantification of typical non-amino organic acids and amino acids. This method exhibited a wide range of linear range, good regression coefficient (R²) and repeatability. The relative standard deviation (RSD) of targeted metabolites showed excellent intra- and inter-day precision (<5%). Our method provided a qualitative and semi-quantitative PCI-GC-MS-MS, coupled with alkyl chloroformate derivatization.