Gas chromatography (GC) is undoubtedly the analytical technique of choice for compositional analysis of petroleum-based fuels. Over the past twenty years, as comprehensive two-dimensional gas ...chromatography (GC × GC) has evolved, fuel analysis has often been highlighted in scientific reports, since the complexity of fuel analysis allows for illustration of the impressive peak capacity gains afforded by GC × GC. Indeed, several research groups in recent years have applied GC × GC and chemometric data analysis to demonstrate the potential of these analytical tools to address important compliance (tax evasion, tax credits, physical quality standards) and forensic (arson investigations, oil spills) applications involving fuels. None the less, routine use of GC × GC in forensic laboratories has been limited largely by (1) legal and regulatory guidelines, (2) lack of chemometrics training, and (3) concerns about the reproducibility of GC × GC. The goal of this review is to highlight recent advances in one-dimensional GC (1D-GC) and GC × GC analyses of fuels for compliance and forensic applications, to assist scientists in overcoming the aforementioned hindrances. An introduction to 1D-GC principles, GC × GC technology (column stationary phases and modulators) and several chemometric methods is provided. More specifically, chemometric methods will be broken down into (1) signal preprocessing, (2) peak decomposition, identification and quantification, and (3) classification and pattern recognition. Examples of compliance and forensic applications will be discussed with particular emphasis on the demonstrated success of the employed chemometric methods. This review will hopefully make 1D-GC and GC × GC coupled with chemometric data analysis tools more accessible to the larger scientific community, and aid in eventual widespread standardization.
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•Gas chromatography is a standard forensic technique for fuel analysis.•GC × GC limited to research due to legal criteria and lack of funding in crime lab.•Higher-dimensional GC data benefits from chemometrics for interpretation.•Separation conditions affect the suitability of resulting data for chemometrics.•Mass spectrometry enhances the amenability of the data for chemometric analysis.
•Iterative investigation strategy based on the informative content of GC×GC patterns.•Cross-validation of GC×GC–MS advanced fingerprinting between two laboratories.•Application of the principles of ...sensomics to reveal the chemical blueprint of EVO.•Identification of informative analytes related to sensory defects.
This study investigates the applicability of an iterative approach aimed at defining a chemical blueprint of virgin olive oil volatiles to be correlated to the product sensory quality. The investigation strategy proposed allows to fully exploit the informative content of a comprehensive multidimensional gas chromatography (GC×GC) coupled to a mass spectrometry (MS) data set. Olive oil samples (19), including 5 reference standards, obtained from the International Olive Oil Council, and commercial samples, were submitted to a sensory evaluation by a Panel test, before being analyzed in two laboratories using different instrumentation, column set, and software elaboration packages in view of a cross-validation of the entire methodology. A first classification of samples based on untargeted peak features information, was obtained on raw data from two different column combinations (apolar×polar and polar×apolar) by applying unsupervised multivariate analysis (i.e., principal component analysis—PCA). However, to improve effectiveness and specificity of this classification, peak features were reliably identified (261 compounds), on the basis of the MS spectrum and linear retention index matching, and subjected to successive pair-wise comparisons based on 2D patterns, which revealed peculiar distribution of chemicals correlated with samples sensory classification. The most informative compounds were thus identified and collected in a “blueprint” of specific defects (or combination of defects) successively adopted to discriminate Extra Virgin from defected oils (i.e., lampante oil) with the aid of a supervised approach, i.e., partial least squares-discriminant analysis (PLS-DA). In this last step, the principles of sensomics, which assigns higher information potential to analytes with lower odor threshold proved to be successful, and a much more powerful discrimination of samples was obtained in view of a sensory quality assessment.
Monitoring exhaled breath is a very attractive, noninvasive screening technique for early diagnosis of diseases, especially lung cancer. However, the technique provides insufficient accuracy because ...the exhaled air has many crucial volatile organic compounds (VOCs) at very low concentrations (ppb level). We analyzed the breath exhaled by lung cancer patients and healthy subjects (controls) using gas chromatography/mass spectrometry (GC/MS), and performed a subsequent statistical analysis to diagnose lung cancer based on the combination of multiple lung cancer-related VOCs. We detected 68 VOCs as marker species using GC/MS analysis. We reduced the number of VOCs and used support vector machine (SVM) algorithm to classify the samples. We observed that a combination of five VOCs (CHN, methanol, CH₃CN, isoprene, 1-propanol) is sufficient for 89.0% screening accuracy, and hence, it can be used for the design and development of a desktop GC-sensor analysis system for lung cancer.
Historically considered to be simple membrane components serving as structural elements and energy storing entities, fatty acids are now increasingly recognized as potent signaling molecules involved ...in many metabolic processes. Quantitative determination of fatty acids and exploration of fatty acid profiles have become common place in lipid analysis. We present here a reliable and sensitive method for comprehensive analysis of free fatty acids and fatty acid composition of complex lipids in biological material. The separation and quantitation of fatty acids are achieved by capillary gas chromatography. The analytical method uses pentafluorobenzyl bromide derivatization and negative chemical ionization gas chromatography–mass spectrometry. The chromatographic procedure provides base line separation between saturated and unsaturated fatty acids of different chain lengths as well as between most positional isomers. Fatty acids are extracted in the presence of isotope-labeled internal standards for high quantitation accuracy. Mass spectrometer conditions are optimized for broad detection capacity and sensitivity capable of measuring trace amounts of fatty acids in complex biological samples. This article is part of a Special Issue entitled Lipodomics and Imaging Mass Spectrometry.
► We review quantitative analyses of fatty acids in biological material. ► Chromatographic separation of fatty acids is achieved by capillary GC. ► Mass spectrometry using soft ionization techniques enables sensitive detection. ► Isotope dilution method facilitates accurate and precise quantitation.
Volatile compounds in Chinese Zhizhonghe Wujiapi (WJP) medicinal liquor were extracted by solvent‐assisted flavor evaporation extraction (SAFE) and stir bar sorptive extraction (SBSE), respectively, ...and identified by gas chromatography‐mass spectrometry. Results showed that a total of 123 volatile compounds (i.e., 108 by SAFE, 50 by SBSE, and 34 by both) including esters, alcohols, acids, aldehydes, ketones, heterocycles, terpenes and terpenoids, alkenes, phenols, and other compounds were identified, and 67 of them were confirmed as aroma‐active compounds by the application of the aroma extract dilution analysis coupled with gas chromatography‐olfactometry. After making a simulated reconstitute by mixing 41 characterized aroma‐active compounds (odor activity values ≥1) based on their concentrations, the aroma profile of the reconstitute showed good similarity to that of the original WJP liquor. Omission test further corroborated 34 key aroma‐active compounds in the WJP liquor. The study of WJP liquor is expected to provide some insights into the characterization of special volatile components in traditional Chinese medicine liquors for the purpose of quality improvement and aroma optimization.
The high potential of exhaled breath for disease diagnosis has been highlighted in numerous studies. However, exhaled breath analysis is suffering from a lack of standardized sampling and analysis ...procedures, impacting the robustness of inter‐laboratory results, and thus hampering proper external validation. The aim of this work was to verify compliance and validate the performance of two different comprehensive two‐dimensional gas chromatography coupled to mass spectrometry platforms in different laboratories by monitoring probe metabolites in exhaled breath following the Peppermint Initiative guidelines. An initial assessment of the exhaled breath sampling conditions was performed, selecting the most suitable sampling bag material and volume. Then, a single sampling was performed using Tedlar bags, followed by the trapping of the volatile organic compounds into thermal desorption tubes for the subsequent analysis using two different analytical platforms. The thermal desorption tubes were first analyzed by a (cryogenically modulated) comprehensive two‐dimensional gas chromatography system coupled to high‐resolution time‐of‐flight mass spectrometry. The desorption was performed in split mode and the split part was recollected in the same tube and further analyzed by a different (flow modulated) comprehensive two‐dimensional gas chromatography system with a parallel detection, specifically using a quadrupole mass spectrometer and a vacuum ultraviolet detector. Both the comprehensive two‐dimensional gas chromatography platforms enabled the longitudinal tracking of the peppermint oil metabolites in exhaled breath. The increased sensitivity of comprehensive two‐dimensional gas chromatography enabled to successfully monitor over a 6.5 h period a total of 10 target compounds, namely α‐pinene, camphene, β‐pinene, limonene, cymene, eucalyptol, menthofuran, menthone, isomenthone, and neomenthol.
Although the coupling of GC/MS with atmospheric pressure ionization (API) has been reported in 1970s, the interest in coupling GC with atmospheric pressure ion source was expanded in the last decade. ...The demand of a “soft” ion source for preserving highly diagnostic molecular ion is desirable, as compared to the “hard” ionization technique such as electron ionization (EI) in traditional GC/MS, which fragments the molecule in an extensive way. These API sources include atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), atmospheric pressure laser ionization (APLI), electrospray ionization (ESI) and low temperature plasma (LTP). This review discusses the advantages and drawbacks of this analytical platform. After an introduction in atmospheric pressure ionization the review gives an overview about the history and explains the mechanisms of various atmospheric pressure ionization techniques used in combination with GC such as APCI, APPI, APLI, ESI and LTP. Also new developments made in ion source geometry, ion source miniaturization and multipurpose ion source constructions are discussed and a comparison between GC-FID, GC-EI-MS and GC-API-MS shows the advantages and drawbacks of these techniques. The review ends with an overview of applications realized with GC-API-MS.
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•Atmospheric pressure ion sources (APCI, ESI, APPI, APLC etc) enable the coupling of LC-based high-end MS to GC.•APIs show advantages in selectivity and sensitivity compared with EI in GC-MS.•Accurate mass database in GC-APCI/MS is emerging as an alternative to GC-EI/MS database.
Multidimensional gas chromatography (MDGC) is now established as a technique which can help resolve most of the co-elution problems presenting with conventional gas chromatography for highly complex ...samples. Essential oils (EOs) are often used in the optimisation and development of novel MDGC methods and related technologies, to demonstrate and assess performance. In this review, recent trends and technical developments in the optimisation of MDGC, modulation and system configuration, pertinent and applied to EO analysis, will be critically discussed. Optimisation of MDGC will be discussed with reference to different column configurations, modulation periods and detection. Attention is given to novel modulation systems, development of multiplex MDGC systems and new approaches which combine heart-cut and comprehensive modes within one system. A section of this review will be dedicated to the preparative application of the MDGC and its application in the isolation of less abundant compounds from complex EO matrices.
•Skatole, sclareololide and sclareololide were first identified in Laoshan tea.•Co-eluted compounds (furfural, cis-linalool oxide) were separating by GC × GC-qMS.•The interactions exist among aroma ...compounds in tea samples.
To investigate the key aroma compounds in Laoshan green teas (Huangshan (S1), Changling (S2), and Fangling (S3)), gas chromatography-mass spectrometry-olfactometry (GC-MS-O), a flame photometric detector (FPD), odor activity value (OAV), and comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC-qMS) were employed. A total of 50 aroma compounds were perceived and 24 compounds were identified as important compounds related to OAV, such as dimethyl sulfide (OAV: 126–146), skatole (OAV: 27–50), furaneol (OAV: 8–27), (Z)-jasmone (OAV: 16–23), 2-methylbutanal (OAV: 15–22), and 3-methylbutanal (OAV: 68–87). Furthermore, the S-curve method was used to research the effect of aroma compounds on the threshold of aroma recombination (AR). The AR thresholds decreased from 3.8 mL to 0.45, 0.66, 0.93, 0.95, 0.75, 1.09, 3.01, and 2.57 mL after addition of eight compounds (skatole, furaneol, (Z)-jasmone, α-damascenone, sclareololide, dihydroactinidiolide, vanillin, and δ-valerolactone), indicating that those compounds (OAV >1) were contributors to the overall aroma of Laoshan teas.
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