Dynamic headspace sampling (DHS) coupled with gas chromatography–mass spectrometry and olfactometry (GC–MS–O) analysis have been applied for the determination of the characteristic volatile profile ...of propolis with the aim to differentiate the propolis from different regions of China. Acids, esters, alcohols, terpenes, aromatics represented the most abundant compounds in propolis among the ninety-nine volatile components identified by comparing with mass spectra and retention indices (RI) or from literature. In addition, principal component analysis (PCA) based on the data of DHS–GC–MS and electronic nose was used to study and obtain the important volatile compounds contributed to the differentiation of the propolis samples from different regions. Furthermore, a total of 28 odor-active compounds were detected and characterized by the trained panel of judges in the sniffing port of GC–O by using detection frequency analysis (DFA). In conclusion, GC–MS analysis and electronic nose combining with PCA could successfully distinguish the twelve representative raw propolis samples from 4 different geographical regions of China. The samples have been assigned to four large groups in accordance with their vegetal sampling location and we also have observed the volatile compounds resulting in the odor differentiation.
► DHS/GC–MS was applied for the determination of the volatile profile of propolis. ► The identification of the geographical origin of propolis was carried out. ► The propolis samples were discriminated by GC–MS coupled with PCA method. ► The propolis samples were discriminated by electronic nose coupled with PCA. ► GC–O was used to identify aroma-active components of propolis.
According to the annual production of plastics worldwide, in 2020 about 370 million tons of plastic were produced in the world. Chemical recycling, particularly pyrolysis of plastic wastes, could be ...a valuable solution to resolve these problems and provide an alternative pathway to produce “recycled” chemical products for the petrochemical industry. Nevertheless, the pyrolysis oils need a detailed characterization before the upgrading test to re-use them to generate new recycled products. Multidimensional gas chromatography coupled with both low- and high-resolution time-of-flight mass spectrometers was employed for a detailed investigation among and within different chemical classes present in bio-plastic oil. The presence of several isomeric species as well as homologs series did not allow a reliable molecular identification, except for a few compounds that showed both MS similarity >800/1000 and retention index within ±20. Indeed, the identification of several isomeric species was assessed by high-resolution mass spectrometry equipped with photoionization interface. This soft ionization mode was an additional filter in the identification step allowing unambiguous identification of analytes not identified by the standard electron ionization mode at 70 eV. The injection method was also optimized using a central composite design to successfully introduce a wide range of carbon number compounds without discrimination of low/high boiling points.
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•GC × GC-LR and HRTOFMS was employed for a deeper bio-plastic oil investigation .•Use of soft ionization MS interface in GC × GC (PI-HRTOFMS) to characterize isobaric molecules not identified using EI at 70 eV.•Optimization of PTV injection using CCD to limit discrimination among low/high boiling points.
•GC×GC enables the characterization of mineral oils detected in foods, supporting the search for the source.•GC×GC enables distinguishing MOSH from POSH as food contaminants.•First dimension GC on a ...polar column provides high selectivity for the saturated hydrocarbons.
Many foods are contaminated by hydrocarbons of mineral oil or synthetic origin. High performance liquid chromatography on-line coupled with gas chromatography and flame ionization detection (HPLC–GC-FID) is a powerful tool for the quantitative determination, but it would often be desirable to obtain more information about the type of hydrocarbons in order to identify the source of the contamination and specify pertinent legislation. Comprehensive two-dimensional gas chromatography (GC×GC) is shown to produce plots distinguishing mineral oil saturated hydrocarbons (MOSH) from polymer oligomeric saturated hydrocarbons (POSH) and characterizing the degree of raffination of a mineral oil. The first dimension separation occurred on a phenyl methyl polysiloxane, the second on a dimethyl polysiloxane. Mass spectrometry (MS) was used for identification, FID for quantitative determination. This shows the substantial advances in chromatography to characterize complex hydrocarbon mixtures even as contaminants in food.
Keemun, Assam, Darjeeling and Ceylon black teas are honored as the world's four most famous black teas, and their excellent aroma qualities are well received by people around the world. In this ...study, aroma components in these four types of teas were analyzed by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-TOFMS) and gas chromatography-olfactometry (GC-O) technologies. A total of 42 aroma-active compounds were ultimately identified, especially benzeneacetaldehyde, geraniol, (Z)-3-hexen-1-yl hexanoate, trans-β-ionone, cis-linalool oxide (pyranoid), hotrienol, and methyl salicylate presented the strongest aroma strengths with pleasant scents in all tested teas. The quantification results indicated that 19 compounds including (Z)-3-hexenol, 1-octen-3-ol, linalool, phenylethyl alcohol, hexanal, benzeneacetaldehyde, limonene, heptanoic acid, (Z)-3-hexen-1-ol, acetate, benzyl alcohol, trans-linalool oxide (furanoid), hotrienol, 1-octen-3-one, 2-nonanone, (E)-2-octenal, nonanal, β-myrcene, 2-pentylfuran, and methylpyrazine were identified as the key compounds with odor activity values (OAVs) higher than 1.0 in the world's four most famous black teas. Notably, the comparison of GC-O and OAV calculation results showed that methyl salicylate (Ceylon), (E)-2-octenal (Assam), benzeneacetaldehyde (Keemun) and linalool and trans-linalool oxide (furanoid) (Darjeeling) might be the most definitive odorants in the corresponding tea categories.
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•Key odorants in world's four most famous black teas were identified and quantified.•Methyl salicylate, 1-octen-3-ol, linalool etc. were key odorants of Ceylon teas.•(E)-2-Octenal, benzeneacetaldehyde, linalool etc. were key odorants of Assam teas.•Benzeneacetaldehyde, hotrienol, nonanal etc. were key odorants of Keemun teas.•Linalool, trans-linalool oxide (furanoid) etc. were key odorants of Darjeeling teas.
Two dimensional GC (GC × GC)–time-of-flight mass spectrometry (TOFMS) has been used to improve accurate metabolite identification in the chemical industry, but this method has not been applied as ...readily in biomedical research. Here, we evaluated and validated the performance of high resolution GC × GC-TOFMS against that of GC-TOFMS for metabolomics analysis of two different plasma matrices, from healthy controls (CON) and diabetes mellitus (DM) patients with kidney failure (DM with KF). We found GC × GC-TOFMS outperformed traditional GC-TOFMS in terms of separation performance and metabolite coverage. Several metabolites from both the CON and DM with KF matrices, such as carbohydrates and carbohydrate-conjugate metabolites, were exclusively detected using GC × GC-TOFMS. Additionally, we applied this method to characterize significant metabolites in the DM with KF group, with focused analysis of four metabolite groups: sugars, sugar alcohols, amino acids, and free fatty acids. Our plasma metabolomics results revealed 35 significant metabolites (12 unique and 23 concentration-dependent metabolites) in the DM with KF group, as compared with those in the CON and DM groups (N = 20 for each group). Interestingly, we determined 17 of the 35 (14/17 verified with reference standards) significant metabolites identified from both the analyses were metabolites from the sugar and sugar alcohol groups, with significantly higher concentrations in the DM with KF group than in the CON and DM groups. Enrichment analysis of these 14 metabolites also revealed that alterations in galactose metabolism and the polyol pathway are related to DM with KF. Overall, our application of GC × GC-TOFMS identified key metabolites in complex plasma matrices.
A fast and mild extraction method and an accurate identification method to analyze the volatiles in non-volatile food matrices were set up. The accelerated solvent extraction followed by solvent ...assisted flavor evaporation (ASE-SAFE) was used to extract the volatiles from Dezhou braised chicken. The extract was analyzed by a comprehensive two-dimensional gas chromatography/high resolution-time of flight mass spectrometry (GC × GC/HR-TOFMS) and a GC-qMS. Ninety one compounds were identified by GC × GC/HR-TOFMS with an aid of the NIST08 library and accurate mass determination, 44 compounds were identified by GC-qMS only with the NIST08 library. The main odor-active constitutes of the Dezhou braised chicken were carbonyl compounds (33.04%). 2-Enals and 2,4-dineals were considered to be the most important odor-active constitutes in chicken. In our study, 6 very polar and unstable 2-enals or 2,4-dineals compounds, including (E)-2-hexenal, (E)-2-nonenal, (Z)-2-decenal, (E)-2-undecenal, (E,E)-2,4-heptadienal and (E,E)-2,4-nonadienal, were only identified by GC × GC/HR-TOFMS. Three very polar and unstable furanones, including 5-acetyldihydro-2(3H)-furanone (0.04%), dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone (0.32%) and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (0.32%) were also only detected by the GC × GC/HR-TOFMS. Some trace sulfur-containing and nitrogen-containing compounds, including disulfide dipropyl (0.05%), 2-acetylthiazole (0.06%), 2-pyrrolidinone (0.15%) and benzothiazole (0.07%) that might play important roles in the flavor of chicken, were also only found by the GC × GC/HR-TOFMS.
•A fast and effective extraction method (ASE-SAFE) is set up.•An accurate identification method (GC × GC/HR-TOFMS) is set up.•Some very polar and unstable odor-active and trace constitutes can be qualified.•6 Compounds of 2-enals or 2,4-dineals are only identified by GC × GC/HR-TOFMS.•The problem of overlapped peaks in TIC of GC-MS is resolved by GC × GC/HR-TOFMS.
The study investigated the volatile compounds of sesame oil and the effects of microwave processing (0–8 min with 1‐min intervals), mainly focusing on the integral flavor characteristics and ...individual aroma‐active compounds. A total of 82 characteristic odors were identified using GC×GC‐TOF/MS. Fifteen volatile compounds with the highest odor activity values (OAV > 100) were selected as the key odors contributing to the flavor profile of microwaved sesame oil, including 2‐methyl‐propanal (pungent, malt, green), 2‐methyl‐butanal (cocoa, almond), furaneol (caramel), 1‐octen‐3‐one (mushroom), 4‐methyl‐3‐penten‐2‐one (sweet), 1‐nonanol (fat, citrus, green), 2‐methyl‐phenol (phenol), 2‐methoxy‐phenol (smoke, sweet), 2‐methoxy‐4‐vinylphenol (clove, curry), 2,5‐dimethyl‐pyrazine (cocoa, roasted nut, roast beef), 2‐furfurylthiol (coffee, roast), 2‐thiophenemethanethiol (sulfur), methanethiol (gasoline, garlic), methional (cooked potato), and dimethyl trisulfide (fish, cabbage). The OAVs significantly increased with a longer microwave process. Meanwhile, PCA results based on E‐nose and cluster analysis results based on GC×GC‐TOF/MS were similar to distinguish flavor formation during the microwave process.
Practical applications
Sesame oils were prepared by a microwave process. Aroma‐active compounds with the highest OAVs in sesame oils were not clear. Identification of key aroma compounds of sesame oils could adopt a comprehensive assessment method in combination with E‐nose and individual odors detection. Microwave pretreatment as a new processing technology for sesame oil extraction could reduce the time consumption and produce a unique fragrant flavor compared to the traditional roasting process.
（1）Volatiles were identified using GC×GC‐TOF/MS in sesame oil from mivrowaved seeds.
（2）15 aroma‐active odors with highest OAV were confirmed.
（3）PCA results in E‐nose is consistent with semi‐quantitative
Incense burning is a common practice in Asian cultures, releasing hazardous particulate organics. Inhaling incense smoke can result in adverse health effects, yet the molecular compositions of ...incense-burning organics have not been well investigated due to the lack of measurement of intermediate-volatility and semi-volatile organic compounds (I/SVOCs). To elucidate the detailed emission profile of incense-burning particles, we conducted a non-target measurement of organics emitted from incense combustion. Quartz filters were utilized to trap particles, and organics were analyzed by a comprehensive two-dimensional gas chromatography-mass spectrometer (GC × GC–MS) coupled with a thermal desorption system (TDS). To deal with the complex data obtained by GC × GC–MS, homologs are identified mainly by the combination of selected ion chromatograms (SICs) and retention indexes. SICs of 58, 60, 74, 91, and 97 were utilized to identify 2-ketones, acids, fatty acid methyl esters, fatty acid phenylmethyl esters, and alcohols, respectively. Phenolic compounds contribute the most to emission factors (EFs) among all chemical classes, taking up 24.5 % ± 6.5 % of the total EF (96.1 ± 43.1 μg g−1). These compounds are largely derived from the thermal degradation of lignin. Biomarkers like sugars (mainly levoglucosan), hopanes, and sterols are extensively detected in incense combustion fumes. Incense materials play a more important role in shaping emission profiles than incense forms. Our study provides a detailed emission profile of particulate organics emitted from incense burning across the full-volatility range, which can be used in the health risk assessments. The data processing procedure in this work could also benefit those with less experience in non-target analysis, especially GC × GC–MS data processing.
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•Homologs from incense burning are identified and quantified in detail.•Selected ion chromatograms (SICs) are of vital importance in identifying organics.•Phenolic compounds contribute the most to emission factors (EFs) taking up 24.5 % ± 6.5 %.
The diversity of chemicals complicates the question of their exposure and risk to humans and biota. It is also becoming harder to detect and accurately understand complex contaminants in the ...environment and in organisms. Attention is increasingly being focused on the search for unknowns of concern, the quantification of substance groups with extremely large numbers of isomers and homologues, and the simultaneous measurement of contaminants with similar toxicities and physical properties. This paper presents two strategies for addressing these analytical problems. The first part outlines recent environmental applications of comprehensive two-dimensional gas chromatography (GC × GC) to high-definition instrumental analysis. The latter part presents examples of computational analysis, including artificial intelligence (AI), as well as various workflows and tools for dealing with the large amounts of information produced from high-definition methods based on chromatography/mass spectrometry (MS).
•Recent GC × GC comprehensive analysis of the growing number of environmental contaminants.•Application of computational science, including artificial intelligence, to suspect screening and non-target analysis of environmental contaminants.•Trends in prediction and optimization of analytical conditions from the structures of substances.•Trends in prediction of (partial) structures, physical properties, and biological activities as derived from analytical data.
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•GC × GC-ToF-MS was a better choice to discriminate the volatile profiles of M. sextelata when compared with GC–MS and GC-IMS.•Alcohols, heterocycles, and ketones were the VOCs most ...affected by the drying methods.•Freeze-drying was beneficial to maintain key flavor substances of M. sextelata, such as C8 compounds and benzaldehyde.•Hot air-drying promoted the production of heterocycles and ketones with roasted flavor.
Morchella sextelata is a precious and popular commercial edible fungus that was developed recently in China. This research aimed to characterize the volatile profiles of M. sextelata under three dehydration methods (freeze, hot air, and natural air drying). Comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC-ToF-MS) was shown to the best choice to discriminate the volatile profiles of M. sextelata Characteristic flavor substances of M. sextelata were eight-carbon-containing (C8) compounds, hexanal, 2(5 h)-furanone, and benzaldehyde. Drying methods had significant influences on the volatile flavor profiles of M. sextelata, and 104 differential compounds were screened by multivariate statistical analysis. Freeze-dried samples had the most abundant volatile compounds and maintained more alcohols, ketones, aldehydes, and esters described as mushroom, sweet, and green flavor, like 1-octen-3-ol, 1-octen-3-one, nonanal, 2,3-butanedione, and so on. Hot air-drying promoted the production of heterocycles and ketones with roasted flavor due to the thermalreaction, such as 2-cyclohexen-1-one, furan, 3-phenyl-, etc. Natural air-drying resulted in acids releasing an unpleasant flavor, e.g., acetic acid, 2-methylbutanoic acid, etc. Overall, thermal reaction combined with vacuum conditions might be suitable for maintaining and enriching the aroma flavor of dried true morels.
