2D GC Research Articles

Exploring the chemogeographical variation of a commercially important medicinal tree (Prunus africana (Hook.f.) Kalkman) using a metabolomics approach

The stem-bark of Prunus africana (Hook.f.) Kalkman (African cherry) is traditionally used for the treatment of stomach ache, chest pain, malaria, fever, diabetes and high blood pressure. A large number of constituents have been isolated from the stem-bark including β-sitosterol and ursolic acid, which were reported to have anti-inflammatory activity. The aim of the study was to establish chemotypic variation among Prunus africana samples collected from three African countries, Cameroon, Democratic Republic of Congo (DRC) and Zimbabwe. Ninety-five stem-bark samples were collected from a total of nineteen populations, 11 in Cameroon (n = 55), 4 in Democratic Republic of Congo (n = 20) and 4 in Zimbabwe (n = 20). The samples were extracted with ethyl acetate, dichloromethane and methanol (1 g in 10 mL, 1 g in 10 mL and 2 mg in 5 µL, respectively). Chemometric analysis of chromatographic data obtained from high-performance thin layer chromatography (HPTLC), ultra performance liquid chromatography coupled with mass spectrometry (UPLC–MS), one-dimensional gas chromatography-time-of-flight-mass spectrometry (1D GC–ToF–MS) and spectroscopic data obtained from proton nuclear magnetic resonance (1H NMR) were done using MetaboAnalyst 4.0 software to explore chemotypic variation. A sample from each country was analysed by two-dimensional gas chromatography-time-of-flight-mass spectrometry (2D GC–ToF–MS) to resolve compounds that co-eluted in the 1D GC analysis. Quantification of selected compounds (β-sitosterol and ursolic acid) were done using a validated ultra performance liquid chromatography-photodiode-array detection (UPLC–PDA) method. The chemical profiles obtained from each of the four techniques were very similar for the samples from each country. The HPTLC profiles for Zimbabwe samples were distinctly different from the other two countries with a unique band at Rf value of 0.80. Multivariate analysis of the HPTLC data (using rTLC software), UPLC–MS, 1D GC–ToF–MS and 1H–NMR data revealed three clusters that were country specific. Chemometric analysis through the construction of PCA and a PLS–DA scores plots was performed, followed by the construction of variable important in projection plots, whereby marker compounds contributing significantly to the separation of the three clusters were selected and tentatively identified. Quantitative analysis revealed that samples from Zimbabwe contained higher levels of β-sitosterol (29.2 – 119 µg/g dry weight (DW) of the extract) compared to DRC and Cameroon, while samples from Cameroon were found to contain the highest levels of ursolic acid (1.80 – 141 µg/g DW of the extract). HPTLC, UPLC–MS, 1D and 2D GC–ToF–MS and 1H–NMR are valid tools for quality control of P. africana plant materials after revealing three clusters of samples collected from the three countries. Cameroon samples had high content of ursolic acid, while Zimbabwe samples showed high levels of β-sitosterol. The number of compounds detected across the three countries by 1D GC–ToF–MS was less compared to 2D GC–ToF–MS, which enhanced separation and resolution.

Screening and identification of antibacterial components in Artemisia argyi essential oil by TLC–direct bioautography combined with comprehensive 2D GC × GC-TOFMS

One of the primary components that contribute to Artemisia argyi 's effectiveness is essential oil, which has an exceptional antibacterial effect that has been well documented. The actual cause of its antibacterial activity and associated mechanism, however, are still not completely understood. For the first time, comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (2D GC × GC-TOFMS) and thin-layer chromatography-direct bioautography (TLC-DB) were employed to investigate its antibacterial components. The antibacterial properties of A. argyi essential oil were investigated, and the antibacterial activity of six compounds was evaluated, using Staphylococcus aureus (S. aureus) and Escherichia coli (E. coil) as test microorganisms. TLC-direct bioautography was used to screen two bioactive clusters. Following 2D GC × GC-TOFMS identification of bioactive clusters, six compounds were evaluated for in vitro antibacterial activity verification. All the components tested displayed antibacterial action. Results showed that α-terpineol and eugenol had high potent antibacterial activity (MIC＜0.62 mg/mL, IC50＜2.00 mg/mL). For complex essential oils from traditional Chinese medicine, this method is efficient for quick screening and identifying antibacterial compounds.

Aralianudaside A, an unusual skeleton triterpenoid saponin with anti-airway inflammatory activity from Aralia elata

Aralianudaside A, a triterpene saponin with an unusual skeleton of pentacyclic triterpenoid, along with a new triterpene glycoside and six known compounds were obtained from the buds of Aralia elata. Their structures were determined through extensive spectral analysis, including HRESIMS, IR, 1D and 2D NMR, glycolysis and GC. All compounds were evaluated for anti-airway inflammatory activity in lipopolysaccharides (LPS)-induced airway epithelial cells (16HBE), compounds 1, 3, 5, 7 and 8 significantly decreased the expression of pro-inflammatory cytokines IL-1β and IL-4.

Validation of the liquid chromatography-comprehensive multidimensional gas chromatography-time-of-flight mass spectrometer/flame ionization detector platform for mineral oil analysis exploiting interlaboratory comparison data

Mineral oils, classified into two main fractions, namely saturated (MOSH) and aromatic hydrocarbons (MOAH), originate from petroleum. Their determination in food is challenging due to the difficulty of isolating them from the matrix and the presence of natural interferences, leading to low reproducibility of the results among different laboratories. Therefore, standardized procedures are highly required to minimize the uncertainty caused by various sources (e.g., integration, interference removal, etc.). However, at present, a few sample preparation procedures have been standardized, while the analytical determination is mainly performed using the hyphenated liquid-gas chromatographic technique coupled with a flame ionization detector (LC-GC-FID). However, LC-GC-FID is still not enough for confirmatory purposes, for which the use of comprehensive 2D GC (GC × GC) has been suggested. Recently, the use of a fully integrated platform for routine and confirmatory purposes has been proposed by Bauwens and co-workers (2022), namely LC-GC × GC-time-of-flight mass spectrometer (ToFMS)/FID.

2-Dimensional Gas Chromatography-Mass Spectroscopy: A Review

Gas Chromatography separates components in time. Mass spectroscopy provides information that aids in the identification and structural elucidation of each component. Comprehensive 2-Dimensional gas chromatography (GC×GC) is a novel technique. The revolutionary aspect of GC x GC, with respect to classical multidimensional chromatography, is that the entire sample is subjected to two distinct analytical separations. The resulting enhanced separating capacity makes this approach a prime choice when GC analysts are challenged with highly complex mixtures. The combination of a third mass spectrometric dimension to a GC x GC system generates the most powerful analytical tool today for volatile and semi-volatile analytes. The present review is focused on the instrumentation of 2D GC-MS, the difference between GC and 2d GC, application of 2d GC-MS have been discussed.

Understanding the mechanism of large-scale template elimination during calcination of Mcm-41

An in-depth study of the thermal detemplation of the MCM-41 was carried out in a designed setup running with a high catalyst loading. Mapping the temperature along the catalyst bed during detemplation provides an understanding of the heat transfer phenomena involved under (an)aerobic conditions. Comparison between the results obtained at low (TG/DTA study) and high sample loadings (fixed-bed reactor) suggest that oxygen presence modifies the detemplation mechanism and high flows increase the local temperature in the bed due to the exothermic nature of hydrocarbon oxidation. Thermal cracking products detected during calcination may be considered a benchmark to deduce the local conditions in the catalyst bed. Despite the differences in detemplation processes, both environments lead to solids with similar structural properties. The use of advanced analytical techniques, such as 2D GC, led to the proposal of a detailed reaction scheme for the detemplation step.

High-Efficiency Two-Dimensional Perfectly Vertical Grating Coupler With Ultra-Low Polarization Dependent Loss and Large Fibre Misalignment Tolerance

A two-dimensional grating coupler (2D GC) with four access waveguides is proposed and demonstrated for polarization independent and perfectly vertical coupling. Benefitting from the perfectly vertical coupling and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> power splitting/combing scheme, broadband polarization independent operation can be achieved. Through grating apodization with etched square holes, a simulated coupling efficiency (CE) of 65% (−1.87 dB) is obtained with a minimum feature size of 180nm which is compatible with the 193-nm deep UV lithography technology. To characterize the device performance, a back-to-back configuration of this 2D GC was fabricated, where phase-delay lines with similar patterns are introduced to ensure the phase equality between different waveguide arms. A CE of 49% (−3.1 dB) was experimentally measured, with a 1-dB bandwidth of 42 nm and PDL below 0.2 dB across the wavelength range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5~\mu \text{m}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6~\mu \text{m}$ </tex-math></inline-formula> . The fibre misalignment tolerance of this device was also investigated by measurement. The excess coupling loss and PDL caused by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm 2~\mu \text{m}$ </tex-math></inline-formula> fibre misalignment are lower than 1 dB and 0.8 dB respectively, and the maximum excess coupling loss and PDL caused by ±2° fibre angle error is 1 dB and 0.7 dB respectively. Finally, optical modulation using this device is preliminarily demonstrated by the embedded thermal-optic functions.

Determination of Naphthenic Acids in Oil Sand Processed Water by Two-Dimensional Gas Chromatography with Quadrupole Time-of-Flight Mass Spectrometry (2D GC-QTOFMS)

Two-dimensional gas chromatography (2D GC)–quadrupole time-of-flight mass spectrometry (QTOFMS) combined with derivatization was applied to determine naphthenic acids (NAs) in oil sand processed water (OSPW). Using the excellent resolution of 2D GC and mass resolution of QTOFMS with derivatization, 8 cyclohexane carboxylic acid isomers, 18 methylcyclohexyl carboxylic acid isomers, and 18 methylcyclohexyl acetic acid isomers were identified. Linear relationships across wide concentration ranges were established with correlation coefficients (R 2) of 0.9995, 0.9992, and 0.9990, for cyclohexanecarboxylic acid, 4-methylcyclohexanecarboxylic acid, and 4-methylcyclohexane acetic acid. The precision, expressed as the relative standard deviation (RSD, n = 5), was from 7. 7–9.5% with recoveries between 72.0% and 84.9%. This method was applied to analyze sewage and showed high concentrations of naphthenic acids in untreated samples.

A review on catalytic pyrolysis for high-quality bio-oil production from biomass

Biomass is a renewable source and potentially sustainable fossil fuel replacement due to its availability, lower processing cost, high conversion, and lower life cycle carbon emissions. Pyrolysis can be used to convert biomass into bio-oil, but the quality of bio-oil is usually poor exhibiting high viscosity, thermal instability, and corrosiveness. This review article is focused on the application of catalytic pyrolysis towards obtaining high-quality bio-oil and advanced techniques for bio-oil characterisation. Structural arrangement (i.e., mesoporous, microporous), number of acid sites (Lewis and Bronsted acid sites), and amount of metal loading play a key role on deoxygenation reactions and selective production of aromatic hydrocarbons. Hierarchical zeolites doped with noble metals favour hydrogenation of C▬O or C〓O and reduce coke deposition in the production of polycyclic aromatics. Overall reaction mechanisms, aromatic yield and selectivity, the effect of Si/Al ratio, and process challenges of metal loaded zeolites are summarized. The advantages and disadvantages of different types of advanced analytical techniques for bio-oil characterisation are also discussed. The results showed that two-dimensional gas chromatography (2D GC) technique can identify 70% of chromatograph from bio-oil analysis. However, there is need to combine analytical techniques to accurately quantify bio-oil components.

Utility of comprehensive GC×GC-TOFMS in elucidation of aromatic hydrocarbon biomarkers

Conventional one-dimensional gas chromatography-mass spectrometry (GC–MS) has been employed for the organic compound analysis since the 1960s. In traditional GC–MS analysis, co-elution can be intense in the chromatographic region occupied by triterpenoids and aromatic steroids and these can form an unresolved complex mixture (UCM) in the total ion chromatogram (TIC). The UCM in routine GC–MS analysis alters the baseline and adds a substantial noise to mass spectra. Here we demonstrate that comprehensive GC×GC-TOFMS with higher peak capacity helps in an improved characterisation of aromatic hydrocarbon biomarkers by resolving many individual peaks. The use of GC×GC-TOFMS achieved exceptional chromatographic separation of higher plant triterpenoids, triaromatic steroids and methylated 2-methyl-2-(4,8,12-trimethyltridecyl) chromans (MTTC) in a complex aromatic fraction of a Cenozoic crude oil from the Tarapur field of the Cambay Basin. Compounds (e.g., des-A-arbora-5,7,9-triene) having scarce abundance that could not be detected with 1D GC–MS analysis were identified by GC×GC-TOFMS. Thus, this approach offers a new avenue to palaeobiological studies, hydrocarbon exploration and evaluation of the distinct palaeodepositonal environments of organic matter.

Complementary chemical characterization of distillates obtained from industrial hemp hurds by thermal processing

This study focused on spectroscopic characterization of slow pyrolysis distillates from three different hemp hurd variates of industrial hemp (Cannabis sativa L). Raw distillates were collected at drying, torrefaction and pyrolysis stage of the slow pyrolysis process starting from room temperature up to the maximum operating temperature of 350 °C. Complementary chemical characterization of the hemp hurd distillate fractions was achieved using Fourier transform infrared (FTIR) spectroscopy, 1D and 2D NMR spectroscopy, comprehensive two-dimensional gas chromatography-mass spectrometry (2D GC–MS) and liquid chromatography–high resolution mass spectrometry (LC–HRMS). These analyses provided information on the concentration of main chemical constituents of distillates, detected valuable, volatile, semivolatile and nonvolatile compounds and their chemical nature as indicated by functional groups. This study reveals the possibility of optimizing the use of hemp hurds as high-value products by utilizing slow pyrolysis for biochar and further processing for distillates.

Biomarkers of photosynthetic sulfur bacteria in Lower Cretaceous crude oils, East Brazilian marginal basin

Diagenetic aromatic carotenoids and degradation products, which are derived from the carotenoids of photosynthetic sulfur bacteria, were characterized in the aromatic fraction of Brazilian Cretaceous crude oils (NE Brazil, Sergipe-Alagoas Basin) by high-temperature comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (HT-GC × GC–TOFMS). Unresolved complex mixtures (UCM), coeluting compounds, and limited mass spectrometric identification were noted by traditional one-dimensional (1D) GC–MS screening of aromatic compounds. Group-type separation on a two-dimensional chromatographic plane, first- and second-dimension retention times (1tR and 2tR, respectively), and mass spectra enabled the assignment of alkylated mono-, di-, tri-, and tetra-aryl hydrocarbons with confidence. A series of diagenetic C40 carotenoids and degraded products, which are likely indicators for green-brown sulfur bacteria, were detected. This finding corroborates previous results, and isorenieratane was relatively more abundant than 2,3,6-trimethylaryl isoprenoids. Moreover, atropisomeric biphenyls (m/z 237), which coeluted using 1D GC–MS analyses, were resolved by GC × GC and identified by mass spectrometry. The identification of minor abundances of chlorobactane, diagenetic biphenyl chlorobactane, and related compounds, for the first time in these Brazilian Cretaceous oils, may indicate a contribution of green sulfur bacteria (Chlorobiaceae) and photic zone euxinia in shallow waters.

Translation of a One-Dimensional to a Comprehensive Two-Dimensional Gas Chromatography Method with Dual-Channel Detection for Volatile Organic Compound Measurement in Forensic Applications.

After its introduction in the early 1990s, comprehensive two-dimensional gas chromatography (GC×GC) has evolved from a separation science research tool to the central component of many industries. Despite the maturity of the technique, some fields remain reluctant to its use in routine applications. In the case of forensic science, some constraints are the strict requirements enforced in forensic laboratories and the time and effort that must be invested for intralaboratory method validation. Concerns may also arise about whether information could be lost when transitioning to a new technique. This study reports on a method translation from conventional one-dimensional (1D) GC to GC×GC, ensuring the integrity of data as conversion is made. The GC was retrofitted with a reverse fill/flush (RFF) flow modulator and equipped with dual-channel detection using a quadrupole mass spectrometer (qMS) and a flame ionization detector (FID). The parallel use of two detectors, where qMS was applied for qualitative identification and FID for quantification, allowed higher flows and slightly wider peaks to be exploited for the analysis of a volatile organic compound (VOC) reference mixture relevant to forensic VOC profiling. Peak quality assessment and calibration curves using GC-qMS and GC×GC-qMS/FID document the transfer and adaptation of the original method without a loss in data quality. Furthermore, the preprocessing and the data analysis processing steps, including calibration and peak quality assessment for each of the three data sets, are explained in detail. This information provides benchmark data for routine laboratories that want to implement a GC×GC approach into routine workflows.

Salt intervention for the diversities of essential oil composition, aroma and antioxidant activities of Kushui rose (R. setate×R. rugosa)

Increasing the output of essential oil (EO) has always been a concern during production, and this challenge has gained more attention from the essential oil industry. The salt process in which petals are immersed in sodium chloride solution in the process of hydrodistillation can effectively enhance the yield of EO, but it is unknown whether the quality of the EO changes after such treatment. Therefore, this study was designed to compare the properties of fresh rose essential oil (FREO) and salt rose essential oil (SREO), including compositions and their contents, characteristic aroma compounds and aroma profiles, as well as antioxidant activities. In the first part of the investigation, the compounds in FREO and SREO were identified by gas chromatography-mass spectrometry (GC/MS) and two-dimensional gas chromatography and time-of-flight mass spectrometry (GC × GC-TOF/MS). The aroma research was evaluated using the odor activity values (OAV), and the antioxidant properties were investigated for the total antioxidant capacity and the ability to scavenge DPPH free radicals. The results identified the 191 and 190 components in FREO and SREO using one-dimensional (1D) GC and two-dimensional (2D) GC, respectively; both were characterized by a high alcohol content, represented particularly by citronellol, geraniol and farnesol. Although some common compounds existed in the two EOs, the same compounds were found in different contents. For example, the citronellol content increased by 31.90 % from 256,491.61 mg/kg to 338,314.45 mg/kg after salt treatment, while the geraniol content decreased by 16.34 % from 47,909.22 mg/kg to 40,080.63 mg/kg. The analysis of aroma showed that salt treatment did not have a strong influence on the aroma types of the EOs as seen from the similar aroma profiles between FERO and SERO, and the performance of antioxidant activities of SREO was superior to that of FREO.

Analysis of defensive secretion of a milkweed bug Lygaeus equestris by 1D GC-MS and GC\xd7GC-MS: sex differences and host-plant effect

The composition of defensive secretion produced by metathoracic scent glands was analysed in males and females of the milkweed bug Lygaeus equestris (Heteroptera) using gas chromatography with mass spectrometric detection (GC-MS). The bugs were raised either on cardenolide-containing Adonis vernalis or on control sunflower seeds in order to determine whether the possibility to sequester cardenolides from their host plants would affect the composition of defensive scent-gland secretion. Profiles of the composition of defensive secretions of males and females raised on sunflower were closely similar, with predominant presence of (E)-2-octenal, (E)-2-octen-1-ol, decanal and 3-octen-1-ol acetate. The secretion of bugs raised on A. vernalis was more sexually dimorphic, and some chemicals e.g. (E,E)-2,4-hexadienyl acetate and 2-phenylethyl acetate were dominant in males, but absent in females. Compared to bugs from sunflower, the scent-gland secretion of bugs raised on A. vernalis was characterized by lower overall intensity of the peaks obtained for detected chemicals and by absence of some chemicals that have supposedly antipredatory function ((E)-2-hexenal, (E)-4-oxo-hex-2-enal, 2,4-octadienal). The results suggest that there might be a trade-off between the sequestration of defensive chemicals from host plants and their synthesis in metathoracic scent-glands.

Cost-effective FTIR and 1H NMR spectrometry used to screen valuable molecules extracted from selected West African trees by a sustainable biochar process

This study focused on wood extractives by a slow pyrolysis thermal extraction technique and screening of potentially valuable compounds from three African trees: Lophira lanceolata Tiegh. ex Keay., Dialium guineense Willd. and Afzelia africana Sm. The primary objective of the thermal treatment was biochar production but also liquids were collected and analyzed. Raw materials were cut into sizes of about 25 cm in length and then processed with slow pyrolysis from 20 °C up to 400 °C; the slow pyrolysis process included two stages, drying and pyrolysis. Five end-point temperatures were used in the range of 250 °C–400 °C. Raw distillates were collected at three temperatures (120 °C, 60 °C and 25 °C) and their composition screened by either cost-effective FTIR or benchtop 80 MHz 1H NMR methods. HR-NMR and 2D GC–MS were used to confirm some findings. Results from the drying stage indicated that all distillates contained mostly water >90%, acetic acid, methanol and some other compounds at very low levels. The percentages of acetic acid were 3.5% for L. lanceolate, 2.8% for D. guineensis and 3.8% for A. africana (% with respect to the identified peaks). Results from the pyrolysis stage revealed the presence of bioactive compounds such as ketones, methanol, hydrocarbons, acetic acid, esters, alkenes and phenolic compounds at higher quantities than in the drying stage. The quantity of phenols in certain runs and distillate fractions using NMR was 1%–20% for L. lanceolata, 7–17% for D. guineensis and 10%–17% for A. africana (% with respect to the composition of the identified peaks). The percentage of hydrocarbons was 1%–48% for L. lanceolata, 1%–34% for D. guineensis and 2%–33% for A. africana. The percentage of ketones was 7%–19% for L. lanceolate, 4%–27% for D. guineensis and 19%–22% for A. africana. In general, the results indicated the presence of potential valuable compounds at relatively high concentrations. By optimizing the slow pyrolysis process parameters, it is possible to collect distillates with high concentrations of valuable biomolecules.

The strength in numbers: comprehensive characterization of house dust using complementary mass spectrometric techniques

Untargeted analysis of a composite house dust sample has been performed as part of a collaborative effort to evaluate the progress in the field of suspect and nontarget screening and build an extensive database of organic indoor environment contaminants. Twenty-one participants reported results that were curated by the organizers of the collaborative trial. In total, nearly 2350 compounds were identified (18%) or tentatively identified (25% at confidence level 2 and 58% at confidence level 3), making the collaborative trial a success. However, a relatively small share (37%) of all compounds were reported by more than one participant, which shows that there is plenty of room for improvement in the field of suspect and nontarget screening. An even a smaller share (5%) of the total number of compounds were detected using both liquid chromatography–mass spectrometry (LC-MS) and gas chromatography–mass spectrometry (GC-MS). Thus, the two MS techniques are highly complementary. Most of the compounds were detected using LC with electrospray ionization (ESI) MS and comprehensive 2D GC (GC×GC) with atmospheric pressure chemical ionization (APCI) and electron ionization (EI), respectively. Collectively, the three techniques accounted for more than 75% of the reported compounds. Glycols, pharmaceuticals, pesticides, and various biogenic compounds dominated among the compounds reported by LC-MS participants, while hydrocarbons, hydrocarbon derivatives, and chlorinated paraffins and chlorinated biphenyls were primarily reported by GC-MS participants. Plastics additives, flavor and fragrances, and personal care products were reported by both LC-MS and GC-MS participants. It was concluded that the use of multiple analytical techniques was required for a comprehensive characterization of house dust contaminants. Further, several recommendations are given for improved suspect and nontarget screening of house dust and other indoor environment samples, including the use of open-source data processing tools. One of the tools allowed provisional identification of almost 500 compounds that had not been reported by participants.

Investigating weathering in light diesel oils using comprehensive two-dimensional gas chromatography–High resolution mass spectrometry and pixel-based analysis: Possibilities and limitations

Petroleum-derived fuels are chronically spilled in urbanized areas, affecting the environment and the population’s health. Forensic investigations of oil spills aim to find the responsible source of the spills. Weathering processes (dissolution, evaporation, photo-oxidation and biodegradation) change the chemical composition of the spills and hamper the matching of spill-source pairs, especially for light diesel oils (i.e. n-C9 – n-C20) in which the source diesels can be very similar due to the refining process and only compounds resistant to short- or middle-term weathering are present. In this study, comprehensive two-dimensional gas chromatography – high resolution mass spectrometry (GC × GC – HRMS) and pixel-based analysis were combined for: i) improve the identification of very similar diesel oils, and ii) identify weathering-resistant compounds that can also distinguish samples from different sources. Diesel oils from two sources that have been exposed to different degrees of evaporation, photo-oxidation and biodegradation in a laboratory setup. The study revealed the tentatively identified octanoic acid methyl ester and n-nonaldehyde were more resistance to evaporation than hydrocarbons < n-C15. Furthermore, the hydrocarbons > n-C17 could be used for source-apportionment of all the diesel oils susceptible to evaporation and photo-oxidation, but only pristane and phytane were also more resistant to biodegradation. Naphthenes, bicyclic sesquiterpanes and adamantanes were more resistant to only photo-oxidation and biodegradation. GC × GC – HRMS enhanced the separation of the highly similar naphthenes in the diesel oils; however, the diagnostic power for forensic spill investigations was still similar to 1D GC – HRMS.

Detection and Quantitation of ACCUTRACE S10, a New Fiscal Marker Used in Low-Duty Fuels, Using a Novel Ultrahigh-Performance Supercritical Fluid Chromatography–Mass Spectrometry Approach

A new ultrahigh-performance supercritical fluid chromatography–mass spectrometry (UHPSFC–MS) method has been developed using electrospray ionization (ESI) to detect and quantify a new fiscal fuel marker, ACCUTRACE S10, that was introduced into fuel in the U.K. and Ireland from April 1, 2015. S10 is synthesized by the Dow Chemical Company and is used as a replacement for ultraviolet–visible (UV–vis) fuel markers, such as quinizarin, Euromarker, and Solvent Red 24. It is UV–invisible, is doped at a low level (2.5 ppm), and was designed for detection using modern gas chromatography–mass spectrometry (GC–MS) instrumentation. All currently proposed methods for the determination of the ACCUTRACE S10 fuel marker in diesel fuel (automotive diesel oil, with current specifications of EN 590 and ASTM D975) use GC–MS, and two-dimensional (2D) GC–MS is necessary to detect the marker at tank dilutions. However, the lower limit of detection (LLOD) and lower limit of quantification (LLOQ) for S10 are severely compromised...

In Vitro Gut Metabolism of [U-13 C]-Quinic Acid, The Other Hydrolysis Product of Chlorogenic Acid.

Quinic acid in its free form is broadly abundant in plants, and can accumulate in copious amounts in coffee, tea, and certain fruits. However, it has been mostly studied as chlorogenic acid, an ester of caffeic and quinic acids. When chlorogenic acid reaches the colon, it is hydrolyzed by microbial esterases releasing caffeic and quinic acids. While biotransformation of chlorogenic and caffeic acids have been elucidated by in vitro and in vivo studies, the gut metabolism of quinic acid has been so far overlooked. [U-13 C]-Quinic acid is submitted to a colonic model using human fecal microbiota for assessing its metabolic fate. The metabolite profiles formed along microbial biotransformation are monitored by a combined metabolomics approach, using both 2D GC- and ultra-HPLC-MS. Six metabolic intermediates are identified by incorporation of isotopic label. Two parallel degradation pathways could be proposed: (1) an oxidative route, leading to aromatization and accumulation of protocatechuic acid, and a (2) reductive route, including dehydroxylation to cyclohexane carboxylic acid. Elucidating the biotransformation of food bioactives by the gut microbiota is of relevance for understanding nutrition, interindividual variability and potential effects on human metabolism.