Comprehensive Two-dimensional Gas Chromatography-mass Spectrometry Research Articles

Comprehensive Two-Dimensional Gas Chromatography-Mass Spectrometry as a Tool for the Untargeted Study of Hop and Their Metabolites.

Since hop secondary metabolites have a direct correlation with the quality of beer and other hop-based beverages, and the volatile fraction of hop has a complex composition, requiring effective separation, here we explore the application of headspace solid-phase microextraction as a sample preparation method, coupled with comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) analysis. The methodology involved the use of a DVB/PDMS fibre with 500 mg of hop cone powder, extracted for 40 min at 50 °C, for both GC-MS and GC×GC-MS. The varieties Azacca, Cascade, Enigma, Loral, and Zappa were studied comprehensively. The results demonstrate that GC×GC-MS increases the number of peaks by over 300% compared to classical GC-MS. Overall, 137 compounds were identified or tentatively identified and categorised into 10 classes, representing between 87.6% and 96.9% of the total peak area. The composition revealed the highest concentration of sesquiterpene hydrocarbons for Enigma, whilst Zappa showed a relatively significant concentration of monoterpene hydrocarbons. Principal component analysis for all compounds and classes, along with hierarchical cluster analysis, indicated similarities between Zappa and Cascade, and Azacca and Loral. In conclusion, this method presents an optimistic advancement in hop metabolite studies with a simple and established sample preparation procedure in combination with an effective separation technique.

A novel headspace solid-phase microextraction arrow method employing comprehensive two-dimensional gas chromatography–mass spectrometry combined with chemometric tools for the investigation of wine aging

BackgroundOmics is used as an analytical tool to investigate wine authenticity issues. Aging authentication ensures that the wine has undergone the necessary maturation and developed its desired organoleptic characteristics. Considering that aged wines constitute valuable commodities, the development of advanced omics techniques that guarantee aging authenticity and prevent fraud is essential. ResultsΑ solid phase microextraction Arrow method combined with comprehensive two-dimensional gas chromatography-mass spectrometry was developed to identify volatiles in red wines and investigate how aging affects their volatile fingerprint. The method was optimized by examining the critical parameters that affect the solid phase microextraction Arrow extraction (stirring rate, extraction time) process. Under optimized conditions, extraction took place within 45 min under stirring at 1000 rpm. In all, 24 monovarietal red wine samples belonging to the Xinomavro variety from Naoussa (Imathia regional unit of Macedonia, Greece) produced during four different vintage years (1998, 2005, 2008 and 2015) were analyzed. Overall, 237 volatile compounds were tentatively identified and were treated with chemometric tools. Four major groups, one for each vintage year were revealed using the Hierarchical Clustering Analysis. The first two Principal Components of Principal Component Analysis explained 86.1% of the total variance, showing appropriate grouping of the wine samples produced in the same crop year. A two-way orthogonal partial least square – discriminant analysis model was developed and successfully classified all the samples to the proper class according to the vintage age, establishing 17 volatile markers as the most important features responsible for the classification, with an explained total variance of 88.5%. The developed prediction model was validated and the analyzed samples were classified with 100% accuracy according to the vintage age, based on their volatile fingerprint. SignificanceThe developed methodology in combination with chemometric techniques allows to trace back and confirm the vintage year, and is proposed as a novel authenticity tool which opens completely new and hitherto unexplored possibilities for wine authenticity testing and confirmation.

Chemometrics combined with comprehensive two-dimensional gas chromatography-mass spectrometry for the identification of Baijiu vintage

The identification of baijiu vintage is crucial for quality assessment and economic value determination. However, its complex composition and multifaceted influences pose significant technical challenges, necessitating research into its aging mechanisms and the development of related identification methods. This study utilized Chemometrics in conjunction with GC × GC-TOFMS for Baijiu Vintage identification. Data compression achieved a reduction of over 1000-fold without compromising key information, enabling analysis on many samples and get their changing regular in a big matrix by MCR. Subsequently, MCR-ALS facilitated the extraction of physical and chemical meaningful information related to baijiu vintage. Key MCR principal components suitable for qualitative and quantitative assessments were selected using CARS-PLS. The regression model demonstrated errors of less than one year. Furthermore, a PLS-DA model provided 30 MCR principal components as potential markers. The research results provide technical support for baijiu vintage identification and lay the groundwork for studying the changing patterns of flavor compounds in baijiu.

Identification of coronavirus disease marker compounds in sweat with comprehensive two dimensional gas chromatography using multiloop splitter-based non-cryogenic artificial trapping modulation system

This study applied comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GCMS–) for analysis of volatile compounds in headspaces of axillary swab samples of RT-PCR or antigen test kit proven COVID-19 positive and negative volunteers in Bangkok, Thailand. The separation was performed using a conventional Deans switch (DS) based heartcut system with an additional splitter system located between the first (1D) column (30 m) and the DS. The splitter consisted of deactivated fused silica (DFS) columns connected into three loops with the progressively doubled perimeters of the downstream loops. An artificial GC × GC result was obtained by applying a periodic heartcut (H/C) event within every artificial modulation period (PAM) of 1.14 min, selectively transferring the analytes onto the second (2D) column (30 m). Chemometric analysis including feature selection was used to identify significantly altered metabolites between the positive and negative groups. Fourteen significant metabolites were tentatively identified, including p-cymene, linalool, and 2,6,11-trimethyldodecane. The marker peak area thresholds were optimized by generating receiver operating characteristic (ROC) curves showing accuracy, sensitivity and selectivity within the ranges of 94–98%, 93–97% and 94–100%, respectively. Based on these results, we hypothesize that SARS-CoV-2 infection disrupts the metabolism of volatile metabolites in sweat, or impacts the microbiome, changing the volatile profile of sweat in infected patients.

Determination of volatile compounds in different parts of grass carp using GC✕GC-MS combined with chemometrics

The flavor of freshwater fish, which is a highly complex mixture of volatile molecules in varying concentrations, has a nasty and earthy odor. Many compounds of freshwater fish cannot be differentiated due to insufficient separation in traditional one-dimensional gas chromatography-mass spectrometry (GC-MS). This study employed an improved method to detect volatile compounds in different parts of grass carp, including the dorsal meat, skin, intestines, belly, fins, and gills. Comprehensive two-dimensional gas chromatography-mass spectrometry (GC✕GC-MS) with high resolution power was utilized to fully separate the volatile compounds. Additionally, an in-house written script based on Matlab and chemometrics was used to conduct large scale and untargeted studies on volatile compounds. The results demonstrated the superior capability of GC✕GC-MS in identifying a greater number of volatile compounds. The in-house written script was used to automatically compare the same compounds from different samples. Through OPLS-DA analysis, 51 key volatile compound candidates, including dihydrojasmone, cryptomeridiol, (Z,Z)-3,6-nonadienal, 3,5-octadien-2-one, and others, were identified as the most-influential variables in differentiating different parts of grass carp. PCA analysis revealed that the 51 key volatile compound candidates still retained information about the origin of different parts, despite their low concentration. Furthermore, expect that most of these compounds have been found in fish or fish-related products, some may originate from plants, insecticides, or pollution.

Complex origins of naphthenic oils in the Junggar Basin, China: Biodegradation vs. non-biodegradation

Naphthenic crude oils are scarce resources of great value. Their origins are generally considered to be related to biodegradation, which consumes paraffins and enriches naphthenes. However, other possible controls on the origins of the naphthenic oils remain insufficiently clear. To fill the knowledge gap, we conducted a case study in the Junggar Basin by using comprehensive two-dimensional gas chromatography–mass spectrometry for semi-quantitative analysis of naphthenes in combination with relevant organic geochemical data, and address its global implications by synthesizing the typical naphthenic oils discovered worldwide. It was found that the occurrence of naphthenic crude oils in the basin was not caused by biodegradation alone, while sedimentary paleoenvironments and source-rock biological inputs (i.e., indicative of organofacies) are important controlling factors. Naphthenic crude oils are mainly derived from dolomitic source rocks of the Permian Fengcheng Formation in the Mahu Sag of the northwestern basin, where the average naphthene content is 43.8 %, with an average naphthene/paraffin (N/P) ratio of 1.24. Source rocks were deposited in a reducing, hypersaline and stratified alkaline lake (0.75 < pristane/phytane (Pr/Ph) < 1.46, gammacerane/C30αβ hopane > 0.23), with source-rock biological inputs being dominated by halophilic algae (steranes/hopanes > 1, C28/C27-29-steranes > 40 %). In contrast, crude oils in the Jimusaer Sag of the southeastern basin are paraffinic–naphthenic with an average naphthene content of 24.8 % and an average N/P ratio of 0.75. Source rocks here were deposited in an anoxic–oxic lake of low salinity (1.05 < Pr/Ph < 1.59, 0.15 < gammacerane/C30αβH < 0.18), and organic matter consists of mixed bacteria, algae, and terrigenous higher plants (steranes/hopanes < 1, C28/C27-29-steranes < 40 %). Thermal maturity and biodegradation also control the composition of naphthenic oils. High thermal maturity promotes cracking of naphthenic groups, whereas moderate biodegradation (rank PM < 6) promotes naphthenic groups by preferentially catabolizing paraffins. Our results suggest that halophilic algae in strongly-reducing alkaline lakes provide important material for the generation of naphthenic oils in the Mahu Sag and the occurrence of naphthenic crude oils is not controlled solely by biodegradation; influencing factors are complex and vary between regions without universality. This may be the reason for their limited and sparse distribution worldwide.

Variation of wine preference amongst consumers is influenced by the composition of salivary proteins

The preferences of consumers for different flavours and aromas in wine are varied and may be explained by inherent factors such as cultural background, wine education and personal taste of the wine consumer. Wine flavour, as perceived in the mouth, includes aroma compounds released through the retronasal pathway, which are shaped by interactions with saliva. Saliva and wine interactions could provide an explanation as to why wine tasters express different preferences for wine. To test this hypothesis, 13 Western and 13 Chinese experienced wine tasters were recruited. Sensory evaluation was performed in formal surroundings to acquire free description-based and perceived sensory intensity data using the Pivot® Profile and continuous scale assessment, respectively. Participants’ saliva samples were collected before the sensory evaluation and spiked into a wine sample to investigate the impact on the wine’s volatile release using comprehensive two-dimensional gas chromatography–mass spectrometry (GC × GC–MS). Saliva samples were subjected to enzyme activity assays and protein composition profiling by Tandem Mass Tag (TMT) quantitative proteomics. The wine tasters showed differences in wine flavour perception, which was supported by the difference in wine volatile release resulting from the addition of saliva. The two groups of participants did not have significant differences in total salivary protein concentrations or the amounts of esterase and α-amylase. However, statistically significant variations in the concentrations of specific proteins (proline-rich proteins (PRPs) and lipocalin-1 (LCN-1); p < 0.01) were found between the two groups. Significant correlations between perceived intensities of wine attributes and concentrations of PRPs and LCN-1 were observed. These results indicate that the composition of proteins in saliva is a factor that influences wine perception and preference. Our results provide a biochemical basis for understanding preference for food based on interactions between aroma compounds and salivary proteins and could be used to suggest foods or beverages to particular cultural groups.

Error rate and similarity determination of latent fingerprint chemistry via 1D GC and GC × GC–MS

In response to the National Academy of Science’s report on Strengthening Forensic Science, many researchers have investigated ways of improving and supplementing pattern-based visual methods for latent fingerprint (LF) analysis. Gas chromatography (GC) has been used to study the initial and aged chemistry of latent fingerprints, along with attempting to statistically asses same source association with donor characteristics. Since LFs are composed of a complex mixture of oil, sweat, and other components, sections within the chromatographic profile that have poor resolution could benefit from better separation of components, thus yielding more associations to the correct source. This study investigates the potential of increased source association using comprehensive two-dimensional (GC × GC) and one-dimensional (1D) gas chromatography-mass spectrometry (GC–MS). Three LFs from a sample of thirteen volunteers were collected, derivatized with boron trifluoride–methanol (BF3-MeOH), and analyzed via 1D GC and GC × GC–MS. The statistical strength of source association was performed by evaluating the log likelihood ratios (LLRs) obtained from the intra- and inter-personal pairwise Pearson correlation comparisons (PCCs) and using the normal and kernel density comparison R functions. The 1D GC method provided stronger same-source association due to high intra-personal PCC values; however, lower inter-personal PCCs were acquired from GC × GC. Higher area under the curves (AUCs) and LLR calibration were computed for the 1D GC PCCs. Conversely, poor statistical calibration and discriminating power were obtained for both 1D GC and GC × GC methods when assessing the LLRs despite having high AUCs.

Analysis, distribution and evolution of individual carboxylic acids in crude oil during biodegradation

Carboxylic acids (CAs) are important molecular markers in the study of petroleum biodegradation. This work presents a vortex-assisted liquid–liquid microextraction (VALLME) method, followed by comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC–MS) analysis for the profiling of CAs in complex oils. The designed extractant containing CAs in VALLME can be silylated immediately and injected into GC × GC–MS without any post-treatment. More than 400 individual CAs, including alkanoic acids, cyclic aliphatic acids and aromatic acids, were putatively or positively identified. With good reproducibility and high sensitivity, VALLME combined with GC × GC–MS was applied to investigate the distribution and evolution of individual CAs in crude oil during laboratory biodegradation. It was found that acyclic acids and monocyclic aliphatic/aromatic acids could be detected at all stages of oil biodegradation, while polycyclic aliphatic/aromatic acids could only be identified in oils at a relatively higher degree of biodegradation. In addition, the contents of each type of CA changed regularly during biodegradation. Targeted analysis on the distributions of individual acyclic acids showed that the abundance ratio of short chain to long chain n-alkanoic acids kept increasing during biodegradation, which might reflect the multiple origins of short chain n-alkanoic acids. Moreover, based on the distributions of pristanic/phytanic acid and pristane/phytane in oils with different biodegradation degrees, pristanic and phytanic acid seemed to be more susceptible to degradation compared to their hydrocarbon analogues, and pristane might be more susceptible to degradation in comparison to phytane.

Solid-phase microextraction Arrow combined with comprehensive two-dimensional gas chromatography-mass spectrometry for the elucidation of the volatile composition of honey samples.

In this work, a solid-phase microextraction (SPME) Arrow method combined with comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-MS) was developed for the elucidation of the volatile composition of honey samples. The sample preparation protocol was optimized to ensure high extraction efficiency of the volatile organic compounds (VOCs) which are directly associated with the organoleptic properties of honey and its acceptance by the consumers. Following its optimization, SPME Arrow was compared to conventional SPME in terms of sensitivity, precision, and number of extracted VOCs. The utilization of SPME Arrow fibers enabled the determination of 203, 147, and 149 compounds in honeydew honey, flower honey, and pine honey, respectively, while a significantly lower number of compounds (124, 94, and 111 for honeydew honey, flower honey, and pine honey, respectively) was determined using conventional SPME. At the same time, the utilization of SPME Arrow resulted in enhanced sensitivity and precision. All things considered, SPME Arrow and GC × GC-MS can be considered as highly suitable for the elucidation of the volatile composition of complex food samples resulting in high sensitivity and separation efficiency.

Non-target screening and prioritization of organic contaminants in seawater desalination brine using comprehensive two-dimensional gas chromatography-mass spectrometry

Non-target screening and prioritization of organic contaminants in seawater desalination brine using comprehensive two-dimensional gas chromatography-mass spectrometry

Sensory and Volatile Compounds Characteristics of the Sauce in Bean Paste Fish Treated with Ultra-High-Pressure and Representative Thermal Sterilization.

This study investigated the differences between three sterilized samples to reveal the unique aroma characteristics of the sauce in bean paste fish by multiple analysis methodologies. Samples were subjected to pasteurized (PS), high-temperature sterilization (HTS), and ultra-high-pressure treatment (UHP) tests. The UHP had a higher sensory evaluation and could better maintain the original flavor of the sample. A total of 92, 83, 85, and 76 volatile compounds were detected via comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) techniques in the control (CT), PS, HTS, and UHP groups, respectively. According to the analysis of gas chromatograph-olfactometry and odor activity value, 7 compounds were considered to have an aromatic influence on the sauces, in which four compounds (1,8-Cineole, Linalool, Hexanal, and Dimethyl trisulfide) exhibited a positive contribution to the aroma of the sauces. PLS-DA results showed that the UHP group positively correlated with volatiles (Isoamylol and 1-Octen-3-ol), color, and gloss. In general, the UHP treatment could retain the original state and flavor of the sauce, showing a high similarity to the control group. The HTS significantly altered the flavor and status of the samples.

Top-Down Approach to Retention Time Prediction in Comprehensive Two-Dimensional Gas Chromatography-Mass Spectrometry.

In this contribution, we describe a novel modeling approach to predicting retention times (tr) in comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-ToF-MS) with a particular emphasis on the second-dimension (2D) retention time predictions (2tr). This approach is referred to as a "top-down" approach in that it breaks down the complete GC × GC separation into two independent one-dimensional gas chromatography separations (1D-GC). In this regard, both dimensions, that is, first dimension (1D) and second dimension (2D) are treated separately, and the cryogenic modulator is simply considered as a second consecutive injection device. Separate 1D-GC tr predictions are performed on both dimensions using the same flow rate as the one deployed in the conventional GC × GC system. The separate tr predictions are then combined to account for the two-dimensional separation. This model was applied to 24 analytes from 2 standard mixtures (Grob Test Mix and Fragrance Materials Test Mix) and assessed across 9 GC × GC chromatographic conditions. The experimental and predicted chromatographic retention space occupations were assessed by using the convex hull approach defined by the Delaunay triangulation. The predicted percentage of space occupation corresponded favorably with the experimental values. Furthermore, the top-down approach enabled an accurate prediction of the 2tr of all investigated analytes, providing an average 2tr modeling error of 0.26 ± 0.01 s.

Possibilities of Using Medicinal Plant Extracts and Salt-Containing Raw Materials from the Aral Region for Cosmetic Purposes.

The aim of this work was to study the possibility of using medicinal plants in combination with salt-containing raw materials from the Aral Sea region for cosmetic purposes. The chemical and mineralogical compositions of salts occurring in this region were studied for pharmacological and cosmetic purposes. The salt-containing raw materials were studied by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The microflora of saline-containing raw materials and flora of the Zhaksy-Klych lake were studied. Fifty-six plant species were identified, of which 25% belong to the Asteraceae family, 32% were Poaceae, 22% were Amaranthaceae, and 21% were Tamaricaceae. Using the solid-phase microextraction (SPME) method and comprehensive two-dimensional gas chromatography–mass spectrometry, the composition of volatile compounds in such plant species as Artemisia alba L., Achilleamillifolium L., Eleagus commutate Bernh. Ex Rydb., Psoraleadrupacea Bunge, Artemisia cipa O. Vegd., Thymus vulgaris L., Morus alba L., Salvia pratensis L., Glycyrhizaglabra L., Tanacetum vulgare L., Polygonumaviculare L., Alhagipseudoalhagi Gagnebin and Peganumharmala L., chosen on the basis of their herbal components for future cosmetic products, was determined. In total, 187 different volatile compounds were found in the endemic plant species Glycyrrhizaglabra L., of which the following were dominant: 1,7-octadiene-3-, 2,6-dimethyl- with a peak area of 4.71%; caryophyllenes; bicyclo[7.2.0]4,11,11-trimethyl-8-methylene-, [1R-(1R*,4E,9S*)]—3.70%; bicyclo[2.2.1] heptane-2-1,7,7-trimethyl-,(1S)—3.46%; cyclohexanone, 5-methyl-2-(1-methylethyledene)-; 2-isopropyledene-5—2.97%; menthol; cyclohexanol, 5-methyl-2-(1-methylethyl)-; p-menthane-3-ol; menthol alcohol; and 2-isopropyl-5—2.08%. The remaining compounds were detected in amounts of less than 2.0%. Tests of seven cosmetic compositions developed on the basis of plant extracts and salt-containing raw materials revealed that three samples had a moisturizing effect. Launching the production of cosmetic products in the Aral region will not only reduce social tensions but also significantly improve the environmental situation in the region.

Retention index based approach for simulation of results and application for validation of compound identification in comprehensive two-dimensional gas chromatography

In this work, first and second dimensional retention index (1I and 2I) based calculation approach is established to simulate peak retention times (1tR and 2tR) of samples for the given sets of volatile compounds in comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS). For the result without 1tR and 2tR data of alkane references (1tR(n) and 2tR(n)), the following steps were applied: (1) curve fitting based on van den Dool and Kratz relationship in order to simulate 1tR(n) using a training set of volatile compounds in a sample with their experimental 1tR data, and (2) simulation of 2tR(n) at different 1tR(n) to construct their isovolatility curves based on a nonlinear equation with p1-p5 parameters and a constant (within the ranges of -0.0052 to 0.0049, -0.6181 to -0.0230, -26.4775 to -0.2698, 0.0050 to 9.6259, -7.2976 to -3.9524 and 0.9157 to 4.0779, respectively). These parameters were obtained by performing curve fitting according to the experimental 2tR data of the same training set with the least square values ranging from 4.58×10−15 to 32.55. Simulation of 1tR and 2tR of target analytes (1tR,sim and 2tR,sim) with known 1I and 2I were performed using 1tR(n) and the simulated isovolatility curves. All the calculations and curve fittings were carried out by using Solver in Microsoft Excel. The approach was applied to simulate results for 542 compounds in several samples including analysis of saffron (Crocus sativas L.), Boswellia papyrifera, acacia honey and incense powder/smoke, perfume and cannabis either reported from literature or from the experiments in this work using different experimental approaches. These were compared with the experimental data showing correlation with the R2 ranges of 0.98–1.00 and 0.80–0.97 for 1tR and 2tR, respectively. This approach was then applied to propose 6 compounds which may be incorrectly identified based on the differences of >2 times of the standard deviations between 2tR,sim and the experimental 2tR in both residue and leave-one-out analyses.

Exploring the volatile profile of whiskey samples using solid-phase microextraction Arrow and comprehensive two-dimensional gas chromatography-mass spectrometry

We present a novel sample preparation method for the extraction and preconcentration of volatile organic compounds from whiskey samples prior to their determination by comprehensive two-dimensional gas chromatography (GC × GC) coupled to mass spectrometry (MS). Sample preparation of the volatile compounds, important for the organoleptic characteristics of different whiskeys and their acceptance and liking by the consumers, is based on the use of the solid-phase microextraction (SPME) Arrow. After optimization, the proposed method was compared with conventional SPME regarding the analysis of different types of whiskey (i.e., Irish whiskey, single malt Scotch whiskey and blended Scotch whiskey) and was shown to exhibit an up to a factor of six higher sensitivity and better repeatability by a factor of up to five, depending on the compound class. A total of 167 volatile organic compounds, including terpenes, alcohols, esters, carboxylic acids, ketones, were tentatively-identified using the SPME Arrow technique, while a significantly lower number of compounds (126) were determined by means of conventional SPME. SPME Arrow combined with GC × GC-MS was demonstrated to be a powerful analytical tool for the exploration of the volatile profile of complex samples, allowing to identify differences in important flavour compounds for the three different types of whiskey investigated.

Changes in volatile profiles of a refrigerated-reheated xylose-cysteine-lecithin reaction model analyzed by GC×GC-MS and E-nose.

The changes in the volatile profiles of a xylose-cysteine-lecithin reaction model were investigated by using comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) in combination with headspace solid-phase microextraction (SPME) and electronic nose (E-nose) to evaluate the contribution of refrigerating and reheating treatment to warmed-over flavor (WOF). The volatile compound results and E-nose revealed that the contribution of refrigerating and reheating to the WOF was not consistent. After refrigerating, the level of furfuryl mercaptan increased, while that of 1-octene-3-ol, octanal, nonanal, and 2-decanone decreased, which affected the flavors. An increase in the level of 1-octene-3-ol, 2-pentyl-thiophene, and hexanoic acid and a decrease in the levels of furfural, 2-methyl-3-furanthiol, and 2-methyl-3-pentanethiol occurred during reheating. According to the odor activity value and sensory evaluation, the sulfur-like odor became more intense after refrigerating, while the rancid-like odor grew stronger, but the sulfur-like odor alleviated after reheating. Overall, the reaction between residual substances caused the WOF during refrigeration, also lead to the fatty acid oxidation increased after reheating. The overproduction of fatty acids oxidation products and decreased of volatile product of Maillard reaction leads to the WOF during reheating. PRACTICAL APPLICATION: This study provides theoretical guidance to reduce the off-flavors of meat products.

Rapid profiling of carboxylic acids in reservoir biodegraded crude oils using gas purge microsyringe extraction coupled to comprehensive two-dimensional gas chromatography-mass spectrometry

Carboxylic acids (CAs) are important molecular markers in petroleum geochemistry, which can indicate the origin, migration and biodegradation of oils. In this work, an easy and fast method was developed for the separation and analysis of CAs in crude oils by the combination of gas purge microsyringe extraction (GP-MSE) and comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC–MS). CAs in oils were firstly reacted with a silylation reagent to improve their volatility and thermal stability. The silylated CAs were then separated from oils together with light hydrocarbons with GP-MSE treatment at a relatively low temperature (200 °C). Subsequently, direct analysis of the extract solutions by GC × GC–MS was performed. Profited from the extremely high peak capacity of GC × GC, the signals of silylated CAs could be easily distinguished from hydrocarbon signals. Under optimal conditions, the extraction time and the solvent consumption of GP-MSE were 8 min and 150 μL, respectively. In the analysis of reservoir crude oils with different biodegradation degrees, abundant CA signals were successfully detected, and the contents of CAs were found to vary regularly with the biodegradation degree.

Comprehensive Two-Dimensional Gas Chromatography-Mass Spectrometry Analysis of Exhaled Breath Compounds after Whole Grain Diets.

Exhaled breath is a potential noninvasive matrix to give new information about metabolic effects of diets. In this pilot study, non-targeted analysis of exhaled breath volatile organic compounds (VOCs) was made by comprehensive two-dimensional gas chromatography–mass spectrometry (GCxGC-MS) to explore compounds relating to whole grain (WG) diets. Nine healthy subjects participated in the dietary intervention with parallel crossover design, consisting of two high-fiber diets containing whole grain rye bread (WGR) or whole grain wheat bread (WGW) and 1-week control diets with refined wheat bread (WW) before both diet periods. Large interindividual differences were detected in the VOC composition. About 260 VOCs were detected from exhaled breath samples, in which 40 of the compounds were present in more than half of the samples. Various derivatives of benzoic acid and phenolic compounds, as well as some furanones existed in exhaled breath samples only after the WG diets, making them interesting compounds to study further.

Screening of semi-volatile compounds in plants treated with coated cerium oxide nanoparticles by comprehensive two-dimensional gas chromatography.

Literature data about semi-volatile organic compounds in plants and the effect of cerium oxide nanoparticles on them are scarce. Surface modification of nanoparticles may change nanoparticle-environment interaction, and therefore affects compounds in plants. In this research, uncoated and glucose-, levan-, and pullulan-coated cerium oxide nanoparticles were used for wheat and pea treatment during the growth. The aim was the screening of semi-volatile organic compounds from plants' shoots using comprehensive two-dimensional gas chromatography-mass spectrometry, a powerful separation technique allowing to reach unique separation resolution, and investigation of qualitative changes after the treatment with coated cerium oxide nanoparticles. The results were analyzed by the identification of individual peaks and fingerprint analysis by image processing. Wheat samples contained a higher number of semi-volatile organic compounds (108) compared to pea (77) but were less affected by the treatments with coated nanoparticles. The highest number of compounds was detected in wheat after the treatment with levan- and pullulan-coated nanoparticles, and in pea after treatment with levan-coated nanoparticles. This article reports a successful application of a semi-volatile organic compounds profile presented only as categorical variables and unique fingerprint images for the inter-cultivar recognition. This method may be useful in screening nanoparticles' effects on different plants.