Comprehensive Two-dimensional Gas Research Articles

Characterization of volatile sulfur compounds in soy sauce aroma type Baijiu and changes during fermentation by GC × GC-TOFMS, organoleptic impact evaluation, and multivariate data analysis

An analytical method based on headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) was developed to characterize volatile sulfur compounds (VSCs) in soy sauce aroma type Baijiu (SSAB) and soy sauce aroma type rounds Baijiu (SSARB). Using this method, 19 VSCs were identified and quantified. The aroma contribution of VSCs was evaluated by odor activity values (OAVs) and perceptive interactions. Seven VSCs had concentrations higher than their corresponding odor thresholds. In particular, the presence of methyl furfuryl disulfide (OAV: 7–11) and 2-methyl-3-(methyldisulfanyl)furan (OAV: 9–18) with relatively high OAVs in Baijiu was reported for the first time, and they could be the important aroma contributors to SSAB. Moreover, sensory analysis revealed that dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide enhanced the perception of fruity aromas in the matrices studied. Partial least-squares discriminant analysis (PLS-DA) analysis indicated that the VSCs could be used to distinguish SSARB.

Untargeted and targeted metabolomics strategy for the classification of strong aroma-type baijiu (liquor) according to geographical origin using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

A metabolomics strategy was developed to differentiate strong aroma-type baijiu (SAB) (distilled liquor) from the Sichuan basin (SCB) and Yangtze-Huaihe River Basin (YHRB) through liquid–liquid extraction coupled with GC×GC-TOFMS. PCA effectively separated the samples from these two regions. The PLS-DA training model was excellent, with explained variation and predictive capability values of 0.988 and 0.982, respectively. As a result, the model demonstrated its ability to perfectly differentiate all the unknown SAB samples. Twenty-nine potential markers were located by variable importance in projection values, and twenty-four of them were identified and quantitated. Discrimination ability is closely correlated to the characteristic flavor compounds, such as acid, esters, furans, alcohols, sulfides and pyrazine. Most of the marker compounds were less abundant in the SCB samples than in the YHRB samples. The quantitated markers were further processed using hierarchical cluster analysis for targeted analysis, indicating that the markers had great discrimination power to differentiate the SAB samples.

Untargeted/Targeted 2D Gas Chromatography/Mass Spectrometry Detection of the Total Volatile Tea Metabolome.

Identifying all analytes in a natural product is a daunting challenge, even if fractionated by volatility. In this study, comprehensive two-dimensional gas chromatography/mass spectrometry (GC×GC-MS) was used to investigate relative distribution of volatiles in green, pu-erh tea from leaves collected at two different elevations (1162 m and 1651 m). A total of 317 high and 280 low elevation compounds were detected, many of them known to have sensory and health beneficial properties. The samples were evaluated by two different software. The first, GC Image, used feature-based detection algorithms to identify spectral patterns and peak-regions, leading to tentative identification of 107 compounds. The software produced a composite map illustrating differences in the samples. The second, Ion Analytics, employed spectral deconvolution algorithms to detect target compounds, then subtracted their spectra from the total ion current chromatogram to reveal untargeted compounds. Compound identities were more easily assigned, since chromatogram complexities were reduced. Of the 317 compounds, for example, 34% were positively identified and 42% were tentatively identified, leaving 24% as unknowns. This study demonstrated the targeted/untargeted approach taken simplifies the analysis time for large data sets, leading to a better understanding of the chemistry behind biological phenomena.

Detection and removal of biologically active organic micropollutants from hospital wastewater

The presence of contaminants of emerging concern (CECs), such as antibiotics, antimicrobial disinfectants, nonprescription drugs, personal care products, pharmaceuticals, and steroids, in water resources can impact aquatic and human health. A large portion of the CECs entering regional wastewater treatment plants originate from hospitals. The purposes of this study were to conduct exploratory analytical work to characterize two hospital wastewaters and to evaluate treatment of CECs at hospitals before dilution with domestic wastewater. A 24-h batch reaction with biogenic manganese oxides coated onto coir fiber was used to treat the wastewaters. Organic contaminants in the wastewaters were concentrated by both liquid-liquid extraction (LLE) and solid-phase extraction (SPE). LLE extracts were analyzed by Comprehensive Two-Dimensional Gas Chromatography/Time-of-Flight Mass Spectrometry (GC × GC-TOFMS) while SPE extracts were analyzedby UltraHigh Performance Liquid Chromatography/Time-of-Flight Mass Spectrometry (UHPLC-TOFMS). Fifty-two organic micropollutants were detected (26 by GC × GC-TOFMS, 25 by UHPLC-TOFMS, 1 by both) in the wastewaters, while 29 were removed by >90% and six were degraded by <50% after treatment. Control experiments revealed that sorption to coir fiber and oxidation by manganese oxides were the primary contaminant removal mechanisms. Both the LLE and SPE extracts were used to evaluate potential human toxicity of the hospital wastewaters before and after treatment. Twenty-eight human cell-based bioreceptor assays were used to screen the wastewaters, and secondary tests were run to quantify toxicity equivalents to activated receptors. The wastewaters initially contained organic micropollutants that strongly activated the Androgen Receptor, Estrogen Receptor β, and the Mineralocorticoid Receptor but no bioactive compounds were detected after treatment. Point-of-entry treatment of hospital wastewater should reduce bioactive compounds from entering the environment.

Complementary Untargeted and Targeted Metabolomics for Differentiation of Extra Virgin Olive Oils of Different Origin of Purchase Based on Volatile and Phenolic Composition and Sensory Quality.

In order to differentiate the extra virgin olive oils (EVOO) of different origin of purchase, such as monovarietal Italian EVOO with protected denomination of origin (PDO) and commercial-blended EVOO purchased in supermarkets, a number of samples was subjected to the analysis of volatile aroma compounds by both targeted gas chromatography/mass spectrometry (GC-MS) and untargeted profiling by comprehensive two-dimensional gas chromatography/mass spectrometry (GC×GC-TOF-MS), analysis of phenols by targeted high-performance liquid chromatography/mass spectrometry (HPLC-DAD-ESI/MS), and quantitative descriptive sensory analysis. Monovarietal PDO EVOOs were characterized by notably higher amounts of positive LOX-derived C6 and C5 volatile compounds, which corresponded to the higher intensities of all the assessed positive fruity and green odor sensory attributes. Commercial-blended EVOOs had larger quantities of generally undesirable esters, alcohols, acids, and aldehydes, which coincided with the occurrence of sensory defects in many samples. Many minor volatile compounds that were identified by GC×GC-TOF-MS were found to differentiate each of the two investigated groups. The differences between the groups with respect to phenols and taste characteristics were evident, but less pronounced. The results that were obtained in this study have undoubtedly confirmed the existence of the large heterogeneity of oils that are sold declared as EVOO. It was shown that GC-MS, GC×GC-TOF-MS, and HPLC-DAD-ESI/MS analyses have complementary outputs, and that their use in combination has advantages in supporting the results of sensory analysis and objectively differentiating these groups of EVOO.

Characterization of the volatile and sensory profile of instant Pu-erh tea using GC × GC-TOFMS and descriptive sensory analysis

Volatile compounds and sensory characteristics of instant Pu-erh teas (IPET) produced through the spray-drying process were evaluated by using headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) and descriptive sensory analysis (DSA), and compared with Pu-erh tea (PET). A total of 208 and 204 volatiles were identified in IPET and PET, respectively. Through independent samples t-test, 98 and 55 compounds showed highly significant differences (P ≤ 0.01) and significant differences (0.01 < P ≤ 0.05) between IPET and PET, respectively. Meanwhile, 158 compounds were defined to interpret the differences between IPET and PET using variable importance in the projection (VIP) value. Moreover，seven aroma attributes were identified through DSA. The results showed that IPET had the higher intensity of floral, fruity, sweet, and caramel-like descriptor, while PET demonstrated higher intensity of stale/musty and woody attributes.

Geochemical Significance of Biomarkers in the Methane Hydrate-Bearing Sediments from the Shenhu Area, the South China Sea

Biomarkers from methane hydrate-bearing sediments can provide vital evidence for microbial activities associated with methanogenesis and their relation to the formation of methane hydrates. However, the former mainly focus on intact polar lipids from these microorganisms, and rarely investigate molecular hydrocarbons such as acyclic isoprenoids and hopanes so far. In this work, the composition of biomarkers in the methane hydrate-bearing sediments in cores SH2B and SH7B from the Shenhu area, the South China Sea (SCS) were identified by gas chromatography-mass spectrometry (GC-MS) and comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC×GC-TOFMS). The occurrence of unresolved complex mixtures (UCMs) and 25-norhopane indicate that the organic matters in methane hydrate-bearing sediments underwent a high degree of biodegradation. Although specific biomarkers for methanogens were not identified, the UCMs, 25-norhopane, pristane, phytane, and hopanes can still indicate the microbial activities associated with methanogenesis. These molecular signals suggest that diverse microorganisms, particularly methanogens, were quite vigorous in the methane hydrate-bearing sediments. Further, the biomarkers identified in this study can also be steadily detected from deep oil/gas reservoirs. Considering numerous adjacent oil/gas reservoir systems, fault systems, and mud diapers occurred in the SCS, it can be inferred that microbial activities and deep oil/gas reservoirs may have jointly contributed to the formation of methane hydrate deposits in the SCS.

Characterization of key aroma compounds in Chinese Guojing sesame-flavor Baijiu by means of molecular sensory science

Key odorants of Guojing sesame-flavor Baijiu were identified using the concept of molecular sensory science, including aroma extract dilution analysis (AEDA) based on gas chromatography–olfactometry (GC–O) combined with gas chromatography-mass spectrometry (GC–MS). A total of 509 volatile compounds were detected by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC × GC–TOF–MS). Sixty-one aroma-active compounds were identified via AEDA. Among them, two compounds with strong roasted aroma showed the highest flavor dilution (FD) factors of 19,683 and 6561. By using pure standards, aroma tests, and GC–MS, the compound with FD = 19683 was identified as benzenemethanethiol, which is reported for the first time in Baijiu. Sixty compounds were quantified by means of internal standard curve method, and 39 of them had odor activity values (OAVs) ≥ 1. Ethyl hexanoate, ethyl octanoate, and dimethyl trisulfide showed the highest OAVs, indicating that they contribute significantly to the aroma of Guojing sesame-flavor Baijiu.

Research Advances on Quality Evaluation Methods of Tea Color, Aroma and Taste

With the progress of the time, the limitations of traditional tea quality evaluation methods have become increasingly prominent. Although the tea quality characteristics can be quickly identified by sensory evaluation, it is also easily affected by some subjective and objective factors. By contrast, determination of chemical components is relatively objective and accurate. However, it is complex to operate and can't reflect the overall quality of the tea. If combined with modern instruments and technologies on the basis of sensory evaluation and physico-chemical analysis, tea quality evaluation can realize advantage complementation and be more comprehensive. In this paper, some new technologies used in tea quality evaluation studies in recent years were summarized in terms of tea color, aroma and taste. Technologies included computer vison and image processing technology, colorimetric sensor array technology, electronic nose technology, comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry technology (GC×GC-TOFMS), gas chromatography and olfactometry technology (GC-O), electronic tongue technology and near infrared spectroscopy technology (NIRS). The development trend of new technology in tea quality evaluation was also discussed.

Volatile composition of Fu-brick tea and Pu-erh tea analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

Dark tea is a special type of tea that requires microbial fermentation during the post-fermentation process, and its volatile composition is quite different from other tea kinds. The present study aimed at charactering the volatile composition of two typical Chinese dark teas (Fu-brick tea and Pu-erh tea). Volatile compounds from both teas were extracted and analyzed using simultaneous distillation extraction (SDE) combined with two-dimensional gas chromatography-time-of-flight-mass spectrometry (GC × GC-TOFMS). A total of 373 and 408 major aromatic components were tentatively identified in Fu-brick tea and Pu-erh tea, respectively. The relative quantification results showed that ketenes (24.87%), ketones (16.86%), aldehydes (14.36%) and olefine aldehydes (9.11%) were more abundant in Fu-brick teas, while in Pu-erh teas, ketenes accounted for 17.95%, followed by aldehydes (14.51%), ally esters and ketones (11.94% and 10.78%). Multivariate analysis indicated that obvious differences existed in the levels of some aromatic compounds between the two dark teas. Benzaldehyde and benzeneacetaldehyde in Fu-brick teas were considerably lower and accounted for approximately 55% of those in Pu-erh teas; whilst, nonanal and 2-hexenal in Fu-brick tea were twice as high as in Pu-erh tea. The application of pre-enrichment extraction with GC × GC-TOFMS analysis gives a thorough view of the aromatic constituents of dark teas.

Identification of key odorants responsible for chestnut-like aroma quality of green teas

A chestnut-like aroma is widely considered an important indicator of an excellent-quality green tea; however, the key odorants responsible for chestnut-like aroma have never been systematically studied and remain unknown. In this study, the aroma components of green teas and Chinese chestnuts were analyzed using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS), and 58 compounds were identified as common aroma components among green teas, boiled Chinese chestnuts, roasted Chinese chestnuts and raw Chinese chestnuts. Subsequently, 17 volatiles, including 3-methylbutanal, (E)-3-penten-2-one, ethylbenzene, heptanal, benzaldehyde, 2-pentylfuran, octanal, benzeneacetaldehyde, (E)-2-octenal, (E,E)-3,5-octadien-2-one, linalool, nonanal, (E)-2-nonenal, decanal, (Z)-hex-3-en-1-yl hexanoate, trans-β-ionone and (E)-nerolidol, were identified as the key odorants responsible for chestnut-like aroma based on the odor activity value (OAV) calculation method. Besides, the comparison of OAVs of key odorants between fresh tea leaves and finished teas indicated that all key odorants were present in fresh tea leaves and that their contents increased or decreased during tea processing. Moreover, the comparison between results of OAV and gas chromatography-olfactometry (GC-O) methods showed that ethylbenzene, heptanal, benzaldehyde, 2-pentylfuran, (E,E)-3,5-octadien-2-one, linalool, (Z)-hex-3-en-1-yl hexanoate and trans-β-ionone were the common identified compounds between the two methods. The identification of chestnut-like aroma in green teas will provide a theoretical basis for further research on the directional adjustment and control of tea aroma quality.

Metabolomic analysis of short-term sulfamethazine exposure on marine medaka (Oryzias melastigma) by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

Toxicological effects of sulfamethazine (SM2) have garnered increasing concern due to its wide applications in aquaculture and persistence in the aquatic environment. Most studies have main focused on freshwater fish (i.e. zebrafish), while information regarding effects of SM2 on marine species is still scarce. Here, the hepatotoxicities in marine medaka (Oryzias melastigma) with an increasing SM2 concentration exposures (0.01 mg/L, 0.1 mg/L and 1 mg/L) were assessed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOF/MS) based metabolomics. Significant metabolites belonging to different metabolites classes were identified by multivariate statistical analysis. The increases levels of amino acids including alanine, asparagine, ornithine, proline, threonine, glutamic acid, lysine, tyrosine and phenylalanine were found in at least two exposure levels. Pathway analysis revealed that amino acids played important biological roles during SM2 exposure: up-regulation of high energy-related amino acids for energy alteration; immune function disorder, oxidative stress and corresponding toxicities defenses. The down regulations of sugar and fatty acid metabolism were observed with an increasing level of SM2 exposure, suggesting that extra energy for cellular defense and detoxification was demanded in terms of different stress request. This study provided an innovative perspective to explore possible SM2 induced hepatic damages at three exposure levels on a nontarget aquatic specie.

Pesticide analysis by pulsed flow modulation GCxGC-MS with Cold EI-an alternative to GC-MS-MS.

We explored the use of pulsed flow modulation (PFM) two-dimensional comprehensive gas chromatography (GCxGC) mass spectrometry with supersonic molecular beams (SMB) (also named Cold electron ionization (EI)) for achieving universal pesticide analysis in agricultural products. The use of GCxGC serves as an alternative to MS-MS in the needed reduction of matrix interference while enabling full-scan MS operation for universal pesticide analysis with reduced number of false negatives. Matrix interference is further reduced with Cold EI in view of the enhancement of the molecular ions. Pulsed flow modulation is a simple GCxGC modulator that does not consume cryogenic gases while providing tuneable second GCxGC column injection time for enabling the use of quadrupole-based mass spectrometry regardless its limited scanning speed. PFM-GCxGC-MS with Cold EI combines improved separation of GCxGC with Cold EI benefits of tailing-free ultra-fast ion source response time and enhanced molecular ions for the provision of increased sample identification information and reduced matrix interference. Consequently, PFM GCxGC-MS with Cold EI also improved NIST library identification probabilities of the spiked pesticides. PFM GCxGC is further characterized by largely increased second column sample and matrix capacity that as a result performs much better than thermal modulation GCxGC-MS with standard EI in the suppression of matrix interference. In a comparison with standard GC-MS, we measured with PFM GCxGC-MS with Cold EI an average total ion count matrix interference reduction factor of 32 for 12 pesticides in two matrices of baby leaves mixture and lettuce. In addition, Cold EI further increases the range of pesticides amenable for GC-MS analysis and its response is relatively uniform hence with it the need for pesticides specific calibration is reduced. Graphical abstract Pulsed flow modulation GCxGC-MS with Cold EI significantly reduces matrix interference and improves sample identification.

A minimally-invasive method for profiling volatile organic compounds within postmortem internal gas reservoirs.

In forensic casework, non-invasive and minimally-invasive methods for postmortem examinations are extremely valuable. Whole body postmortem computed tomography (PMCT) is often used to provide visualization of the internal characteristics of a body prior to more invasive procedures and has also been used to locate gas reservoirs inside the body to assist in determining cause of death. Preliminary studies have demonstrated that exploiting the volatile organic compounds (VOCs) located in these gas reservoirs by comprehensive two-dimensional gas chromatography-high-resolution time-of-flight mass spectrometry (GC×GC-HRTOF-MS) may assist in providing information regarding the postmortem interval. The aim of the current study was to further develop the procedures related to solid-phase microextraction (SPME) and GC×GC-HRTOF-MS analysis of gas reservoirs collected from deceased individuals. SPME fiber extraction parameters, internal standard approach, and sample stability were investigated. Altering the SPME parameters increased the selectivity and sensitivity for the VOC profile, and the use of a mixed deuterated internal standard contributed to data quality. Samples were found to be stable up to 6weeks but were recommended to be analyzed within 4weeks due to higher variation observed beyond this point. In addition, 29 VOC markers of interest were identified, and heart and/or abdominal cavity samples were suggested as a possible standardized sampling location for future studies. The data presented in this study will contribute to the long-term goal of producing a routine, accredited method for minimally-invasive VOC analysis in postmortem examinations.

Analysis of Components of Rocket Kerosene by Comprehensive Two-Dimensional Gas Chromatography/Time-of-Flight Mass Spectrometry

The components of rocket kerosene were determined by comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GCЧGC/TOFMS) under pre-defined analytical conditions. Qualitative analysis was performed by identification of the various groups of the compound on a structured chromatogram. Quantitative analysis was performed by estimating the areas of the respective characteristic peaks. It was found that the kerosene contained paraffins, monocyclic, bicyclic, and tricyclic alkanes, alkenes, and aromatic and oxygen-containing compounds. It was demonstrated that GCЧGC/TOFMS has obvious advantages over traditional methods for determining the components of rocket kerosene.

Study of sewage sludge pyrolysis liquids using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry

The pyrolysis of a Shanghai municipal sewage sludge sample was conducted using a slowly heating and gas sweeping fixed-bed reactor. The pyrolysis liquids produced at three predetermined temperatures (400, 500 and 700°C) were fully examined using GC×GC-TOFMS. The pyrolysis mechanism of the sewage sludge was analyzed online using in situ FTIR from ambient temperature to 600°C. The primary objectives of this study are to (i) determine the chemical composition of the pyrolysis liquids, and (ii) to assess the effect of temperature on the composition of the liquid products. Whereas studies that use GC–MS have normally found hundreds of compounds, analysis of the pyrolysis liquids by GC×GC-TOFMS detected thousands of compounds. Moreover, this method detected some isomers as well. Pyrolysis in this pyrolyzer was observed to produce abundant cyclosiloxanes, which were rarely reported in previous studies, and this may be related to the use of a comprehensive analytical method (GC×GC-TOFMS). The temperature dramatically affected the liquid composition. The proportions of monoaromatics and polyaromatic ketones increased with increasing temperature, and theoretically, the high temperature could promote the production of phenyl rings. The generation of long-chain aliphatic amides and nitriles occurred mainly below 400°C, whereas nitrogen-containing alicyclic hydrocarbons were generated mainly at 500°C. The cyclosiloxanes were part of the original composition of the sewage sludge and were predominantly released below 400°C. The variation in the functional group of the sewage sludge was consistent with that of the pyrolysis gas and liquid compositions.

The influence of ageing and surface type on the odour profile of blood-detection dog training aids

Cadaver-detection dogs are a preferred search tool utilised by law enforcement agencies for the purposes of locating victim remains due to their efficiency and minimal disturbance to the crime scene. In Australia, a specific group of these canines are blood-detection dogs, which are trained to detect and locate blood evidence and search potential crime scenes in cases where a cadaver may not be present. Their role sometimes requires searches to be carried out after considerable time has passed since the crime occurred, and this is important for developing effective training protocols. This study aimed to investigate the volatile organic compounds (VOCs) produced from fresh and aged human blood on various surfaces. Solid phase microextraction (SPME) was used to extract VOCs from the headspace of dried blood samples aged and sampled periodically over 12 months from a non-porous (i.e. aluminium) and porous (i.e. cotton) surface. Samples were analysed using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS). Fresh blood produced distinctively different VOC patterns compared to blood aged longer than 1week with the overall profile differing between the two surface types, and a large subset of the VOC profile found to be responsible for these differences. When analysing the various functional groups present in the samples, a common pattern between ages and surface types was observed with no specific chemical class dominating the overall profile. The results highlight the importance of evaluating training aids for scent-detection canines to ensure the greatest efficacy during training and subsequently at crime scene searches.

Nontargeted evaluation of the fate of steroids during wastewater treatment by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry.

Emerging organic contaminants in wastewater are usually analyzed by targeted approaches, and especially estrogens have been the focus of environmental research due to their high hormonal activity. The selection of specific target compounds means, however, that most of the sample components, including transformation products and potential new contaminants, are neglected. In this study, the fate of steroidal compounds in wastewater treatment processes was evaluated by a nontargeted approach based on comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. The potential of the nontargeted approach to generate comprehensive information about sample constituents was demonstrated with use of statistical tools. Transformation pathways of the tentatively identified compounds with steroidal four-ring structure were proposed. The purification efficiency of the wastewater treatment plants was studied, and the distribution of the compounds of interest in the suspended solids, effluent water, and sludge was measured. The results showed that, owing to strong adsorption of hydrophobic compounds onto the solid matter, the steroids were mostly bound to the suspended solids of the effluent water and the sewage sludge at the end of the treatment process. The most abundant steroid class was androstanes in the aqueous phase and cholestanes in the solid phase. 17β-estradiol was the most abundant estrogen in the aqueous phase, but it was only detected in the influent samples indicating efficient removal during the treatment process. In the sludge samples, however, high concentrations of an oxidation product of 17β-estradiol, estrone, were measured.

A New Approach for the Characterization of Organic Residues from Stone Tools Using GC×GC-TOFMS

Headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) have traditionally been used, in combination with other analyses, for the chemical characterization of organic residues recovered from archaeological specimens. Recently in many life science fields, comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) has provided numerous benefits over GC-MS. This study represents the first use of HS-SPME-GC×GC-TOFMS to characterize specimens from an experimental modern reference collection. Solvent extractions and direct analyses were performed on materials such as ivory, bone, antlers, animal tissue, human tissue, sediment, and resin. Thicker film column sets were preferred due to reduced column overloading. The samples analyzed by HS-SPME directly on a specimen appeared to give unique signatures and generally produced a higher response than for the solvent-extracted residues. A non-destructive screening approach of specimens may, therefore, be possible. Resin and beeswax mixtures prepared by heating for different lengths of time appeared to provide distinctly different volatile signatures, suggesting that GC×GC-TOFMS may be capable of differentiating alterations to resin in future studies. Further development of GC×GC-TOFMS methods for archaeological applications will provide a valuable tool to uncover significant information on prehistoric technological changes and cultural behavior.

Separation of aroma components in Xihu Longjing tea using simultaneous distillation extraction with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

Abstract Aroma is one of the most important determinants of tea quality; thus, the precise characterization of the chemical composition of tea aroma is of significant value. In this study, aroma components of the most famous Chinese green tea, Xihu Longjing tea, were first systematically analyzed using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) combined with simultaneous distillation extraction (SDE). 478 volatile compounds were identified as common constituents of fifty-five Xihu Longjing tea samples based on standard mass spectra in available databases, retention times, retention indices, structured chromatograms and standards. Subsequently, the aroma qualities of Xihu Longjing tea samples were discriminated by sensory evaluation combined with multivariate analysis. The study results indicated that 37 compounds were positively correlated with aroma quality, and 65 compounds were negatively correlated with aroma quality. The above compounds with various odor characteristics were considered as the key components to affect the aroma quality of Xihu Longjing tea.