The impact of comprehensive two-dimensional gas chromatography on oil & gas analysis: Recent advances and applications in petroleum industry

Discrimination of plastic waste pyrolysis oil feedstocks using supercritical fluid chromatography

Advanced chemical recycling techniques provide new avenues for handling and recycling mixed plastic waste; pyrolysis is a prominent approach involving heating plastic waste in an oxygen-free environment to create pyrolysis oils. Pyrolysis oils must be thoroughly characterized before being refined into fuels and chemical feedstocks. Here, a method based on supercritical fluid chromatography with ultraviolet detection was developed to analyze plastic waste pyrolysis oils. Multiple stationary phases were examined, and 2-ethyl pyridine was chosen as the best stationary phase for resolving pyrolysis oil components. Different standards and different plastic waste pyrolysis oils were compared across the different stationary phases. Up to three columns were serially coupled to increase efficiency and column capacity. It was found that a general method using ethanol as a modifier and two 2-ethyl pyridine columns could effectively resolve plastic waste pyrolysis oils. The potential for differentiating polyethylene and polypropylene feedstocks was demonstrated using principal component analysis.

A minireview on covalent organic frameworks as stationary phases in chromatography

Advances in the design of novel porous materials open new avenues for the development of chromatographic solid stationary phases. Covalent organic frameworks (COFs) are promising candidates in this context due to their remarkable structural versatility and exceptional chemical and textural properties. In this minireview, we summarize the main strategies followed in recent years to apply these materials as stationary phases for chromatographic separations. We also comment on the perspectives of this new research field and potential directions to expand the applicability and implementation of COF stationary phases in analytical systems.

Classification of produced water samples using class-oriented chemometrics and comprehensive two-dimensional gas chromatography coupled to mass spectrometry

Produced water (PW) is a type of wastewater that arises during oil and gas production. Due to its potential environmental impact, PW is one of the most closely monitored forms of wastewater in the petroleum industry. The total oil and grease (TOG) content in the water is a crucial parameter for assessing the environmental impact of PW. Traditional methods for analyzing TOG in PW can be time-consuming and may not be compatible with green chemistry principles. In this study, an alternative method for classifying PW samples is proposed using a one-class classifier (OCC) model, which has proven useful for classification problems. To achieve this goal, headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography (GC×GC) were employed to obtain TOG profiles from PW. A series of simulated PW samples containing TOG were generated using a mixture design comprising four petrochemicals at concentrations ranging from 10 mg L-1 to 50 mg L-1. The polydimethylsiloxane (PDMS) fiber showed the most representative extraction of analytes. The optimization of the HS-SPME method was performed using a Doehlert design with two variables, and the final conditions were set at 80 °C and 70 min for extraction temperature and time, respectively. A pixel-based data approach was used to implement data-driven soft independent modeling by class analogy (DD-SIMCA). Although DD-SIMCA is a developing area in GC×GC studies, the proposed model produced outstanding results with a sensitivity of 94.3 %, specificity of 95.0 %, and accuracy of 94.5 %, considering the complex and broad compositional range of the modeled mixtures. These findings demonstrated the effectiveness of the OCC model approach in classifying PW samples according to environmental regulations.

Comprehensive Two-Dimensional Gas Chromatography in Petroleum Derived Samples: A Review on Advances in Source and Weathering Studies of Spilled Oil

Since its introduction comprehensive two-dimensional gas chromatography (GC × GC) has been widely applied to analyze complex samples due to its enhanced peak capacity and selectivity, thereby increasing the number of identifiable peaks and improving coelution issues. Even though it is still undergoing development, GC × GC provides many advantages in the analysis of petroleum-derived samples, whether in reservoir geochemistry applications or in environmental studies associated with spilled oils. In general, it facilitates more thorough fingerprinting and compositional evaluation. In environmental studies, it helps enhance understanding of weathering processes and the environmental behavior of hydrocarbons, as its chromatographic retention indices can robustly estimate liquid vapor pressures, aqueous solubility and other physical chemical properties. This review presents a brief history of GC × GC instrumentation, discussing recent and significant advances in petroleum applications, from data handling techniques to reservoir geochemistry and environmental forensics, as well as some specific advantages achieved and certain limitations that continue to be encountered.

Quality by design-based capillary electrophoresis method development for the quantitative analysis of four iridoid compounds in Gentiana macrophylla Radix

In this study, the capillary electrophoresis-photodiode array detector was employed for the analysis of four iridoid compounds in Gentiana macrophylla Radix (RGM), and the method was optimized based on the concept of analytical quality by design (AQbD). The peak areas relative standard deviation (n = 3) and resolution of the four analytes were selected as critical method attributes. Fractional factorial design test combined with Pareto analysis were employed to screen critical method parameters (buffer concentration, pH, sodium dodecyl sulfate [SDS] micelle concentration, temperature, and voltage). Subsequently, three main factors (buffer concentration, buffer pH, and SDS concentration) were selected by central composite design test for constructing the design space. The optimal separation conditions as follows: capillary column (50.2 cm ×m50 µm, detection length 40 cm). Working background electrolyte consisted of 51 mmol/L borax solution (pH = 9.47) and 40 mmol/L SDS. The samples were injected by pressure (5 s at 0.5 psi) and the detection was performed at 254 nm. Applied voltage was 20 kV and column temperature was 23°C. The developed method is rapid and reliable for the quantitative analysis of four iridoid compounds in RGM, providing a reference for the application of AQbD concept in the analysis of natural products.

The Use of Polydialkylsiloxanes/Triflic Acid as Derivatization Agents in the Analysis of Sulfur-Containing Aromatics by "Soft"-Ionization Mass Spectrometry

Polycyclic aromatic sulfur-containing compounds are widely distributed in oil, especially in its low-volatile and heavy fractions (resins, asphaltenes), and this dictates the need for their determination when reliable methods for sulfur removing, cleaning and processing oil are developed. In these cases, "soft" ionization mass spectrometry methods, based on electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), are particularly effective. However, aromatic sulfur-containing compounds have low polarity and cannot be readily ionized by these methods. To overcome the problem, their preliminary conversion into sulfonium salts by the action of alkyl iodides and a silver-containing agent is widely used. In the process of developing more economical derivatization methods, we found a rather unexpected possibility of implementing S-alkylation of organic sulfides with commercial polydialkylsiloxanes (alkyl = CH₃ or C₂H₅) in the presence of triflic acid (CF₃SO₃H) as a superacid co-alkylating agent. For homologous dibenzothiophenes as a typical model representative of petroleum sulfur-containing aromatic compounds, ESI and MALDI mass spectra exhibited the signals of corresponding S-alkylsulfonium salts with a high signal-to-noise ratio. A rational mechanism for the described chemical transformation is proposed, including the indispensable activation by triflic acid and the cleavage of the Si-C bond. Specific collision-induced dissociation of corresponding S-alkylated sulfonium cations is considered. The applicability of the derivatization approach to the analysis of petroleum products by high-resolution mass spectrometry is demonstrated.

Simulating comprehensive two-dimensional gas chromatography mass spectrometry data with realistic run-to-run shifting to evaluate the robustness of tile-based Fisher ratio analysis

Untargeted analysis of comprehensive two-dimensional (2D) gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) data has the potential to be hindered by run-to-run retention time shifting. To address this challenge, tile-based Fisher ratio (F-ratio) analysis (FRA) has been developed, which utilizes a supervised, untargeted approach involving a chromatographic segmentation routine termed "tiling" combined with the ANOVA F-ratio statistic to discover class-distinguishing analytes while minimizing false positives arising from shifting. The tiling algorithm is designed to account for retention shifting in both separation dimensions. Although applications of FRA have been reported, there remains a need to thoroughly evaluate the robustness of FRA for different levels of run-to-run retention shifting in order to broaden the scope of its application. To this end, a novel method of simulating GC×GC-TOFMS chromatograms with realistic run-to-run shifting is presented by random generation of low-frequency "shift functions". The dimensionless retention-time precision, <δ_r>, which is four times the standard deviation in retention time normalized to the peak width-at-base is used as a key modeling variable along with the 2D chromatographic saturation, α_e,2D, and within-class relative standard deviation in peak area, RSD_wc. We demonstrate that all three of these variables operate together to impact true positive discovery. To quantify the "success" of true positive discovery, GC×GC-TOFMS datasets for various combinations of <δ_r>, α_e,2D, and RSD_wc were simulated and then analyzed by FRA using a wide range of relative tile areas (RTA), which is a dimensionless measure of tile size. Since each hit in the FRA hit list was known a priori as either a true or false positive based on the simulation inputs, receiver operating characteristic (ROC) curves were readily constructed. Then, the area under the ROC curve (AUROC) was used as a metric for discovery "success" for various combinations of the modeling variables. Based on the results of this study, recommendations for tile size selection and experimental design are provided, and further supported by comparison to previous tile-based FRA applications. For instance, values for <δ_r>, α_e,2D, and RSD_wc obtained from a GC×GC-TOFMS dataset of yeast metabolites suggested an optimum RTA of 6.25, corresponding closely to the RTA of 4.00 employed in the study, implying the simulation results obtained here can be generalized to real datasets.

Profiling Olefins in Gasoline by Bromination Using GC×GC-TOFMS Followed by Discovery-Based Comparative Analysis

An analytical workflow for the analysis of olefins in gasoline that combines selective bromination and comprehensive two-dimensional (2D) gas chromatography time-of-flight mass spectrometry (GC×GC-TOFMS) with discovery-based analysis is reported. First, a standard mix containing n-alkanes, 1-alkenes, and aromatic species was brominated and quantified using % reacted as a metric for each compound class, defined as the difference in the total peak area between the brominated and original samples normalized to the original sample. The average % reacted (1 s.d.) values were -1.45% (2.8%) for the alkanes, 99.5% (0.4%) for the alkenes, and 6.7% (11.6%) for the aromatics, demonstrating excellent selectivity toward the alkenes with only minor aromatic bromination. The bromination chemistry was then applied to gasoline, followed by GC×GC-TOFMS analysis of the original and brominated gasoline. This GC×GC-TOFMS data set was then submitted to the supervised discovery tool tile-based F-ratio analysis (FRA), which reduced the large data set to only the chromatographic regions which distinguish between the original and brominated gasoline samples. FRA discovered 314 hits, 56 of which were determined statistically significant using combinatorial null distribution analysis (CNDA), a permutation-based significance test. Since the brominated olefins elute in an uncrowded region of the 2D chromatogram and have no signal in the original sample, their discoverability was greatly increased relative to the original olefins. By combining the information gained from brominated olefin standards and the structured patterns of the GC×GC separations, the top hits were identified as the dibromoalkane products of mono-olefins, with five C5 mono-olefins identified on a species level. The analytical workflow has broad implications for using selective reaction chemistries to facilitate supervised discovery by targeting desired compound classes.

Advanced tuning of the ion management parameters in GC × GC-HRMS using a Fourier transform Orbitrap mass analyzer for pixel-based data handling and multivariate analysis

GC × GC investigations are well known to generate a substantial amount of information-rich and structurally complex data, requiring advanced data processing strategies like chemometrics. Many workflows are available for data handling and processing, such as the peak-table and pixel-based approaches. The goal of this work is to present a solution based on method development to solve the missing pixel problem that may be encountered in experiments performed with GC and GC × GC coupled to the Fourier transform orbital ion trap (FT-Orbitrap) mass analyzer. Data input is vital for pixel-based chemometric analyses, as some post-processing solutions may lead to significant loss of chemical information in the data set. Hence, a key requisite is that the chemical information is consistently indexed in the data arrays for proper pixel-based data handling and analysis. In this study, we carefully evaluated the ion management parameters to preserve the intrinsic structure and information of the data arrays of the GC × GC-FT-Orbitrap for future pixel-oriented chemometric analysis. The most acceptable conditions yielded acquisition rates up to 42.6 spectra per s, while a routine setting of 24.7 Hz was successfully employed in analyses of different petroleum fractions, producing both consistent tensor sizes and acceptable peak reconstructions. A data acquisition rate of 24.7 spectra per s and a mass resolving power of 15 000 allowed the resolution of a mass split of only 0.004 Da - which is an interesting configuration for challenging applications in petroleomics. Using such advanced settings, the missing pixel problem was reduced from up to 30% to much less than 0.04% of the data array dimension. Thus, the proposed configuration can be employed in studies that require pixel-oriented multivariate data analysis.

Advances in Chemical Analysis of Oil Spills Since the Deepwater Horizon Disaster

Analytical techniques for chemical analysis of oil, oil photochemical and biological transformation products, and dispersants and their biodegradation products benefited significantly from research following the 2010 Deepwater Horizon (DWH) disaster. Crude oil and weathered-oil matrix reference materials were developed based on the Macondo well oil and characterized for polycyclic aromatic hydrocarbons, hopanes, and steranes for use to assure and improve the quality of analytical measurements in oil spill research. Advanced gas chromatography (GC) techniques such as comprehensive two-dimensional GC (GC × GC), pyrolysis GC with mass spectrometry (MS), and GC with tandem MS (GC-MS/MS) provide a greater understanding at the molecular level of composition and complexity of oil and weathering changes. The capabilities of high-resolution MS (HRMS) were utilized to extend the analytical characterization window beyond conventional GC-based methods to include polar and high molecular mass components (>400 Da) and to provide new opportunities for discovery, characterization, and investigation of photooxidation and biotransformation products. Novel separation approaches to reduce the complexity of the oil and weathered oil prior to high-resolution MS and advanced fluorescence spectrometry have increased the information available on spilled oil and transformation products. HRMS methods were developed to achieve the required precision and sensitivity for detection of dispersants and to provide molecular-level characterization of the complex surfactants. Overall, research funding following the DWH oil spill significantly advanced and expanded the use of analytical techniques for chemical analysis to support petroleum and dispersant characterization and investigations of fate and effects of not only the DWH oil spill but future spills.

Unraveling the Complex Composition of Produced Water by Specialized Extraction Methodologies

Produced water (PW), a waste byproduct of oil and gas extraction, is a complex mixture containing numerous organic solubles and elemental species; these constituents range from polycyclic aromatic hydrocarbons to naturally occurring radioactive materials. Identification of these compounds is critical in developing reuse and disposal protocols to minimize environmental contamination and health risks. In this study, versatile extraction methodologies were investigated for the untargeted analysis of PW. Thin-film solid-phase microextraction with hydrophilic-lipophilic balance particles was utilized for the extraction of organic solubles from eight PW samples from the Permian Basin and Eagle Ford formation in Texas. Gas chromatography-mass spectrometry analysis found a total of 266 different organic constituents including 1,4-dioxane, atrazine, pyridine, and PAHs. The elemental composition of PW was evaluated using dispersive solid-phase extraction followed by inductively coupled plasma-mass spectrometry, utilizing a new coordinating sorbent, poly(pyrrole-1-carboxylic acid). This confirmed the presence of 29 elements including rare earth elements, as well as hazardous metals such as Cr, Cd, Pb, and U. Utilizing chemometric analysis, both approaches facilitated the discrimination of each PW sample based on their geochemical origin with a prediction accuracy above 90% using partial least-squares-discriminant analysis, paving the way for PW origin tracing in the environment.

Sulfolane as a novel stationary phase for analytical separations by gas chromatography

Sulfolane is explored as a novel stationary phase for use in analytical separations by capillary column gas chromatography with flame ionization detection (GC-FID). Stainless steel capillaries were found to provide a good substrate for coating and retaining a sulfolane phase, whereas fused silica tubing did not perform well for this. In general, the phase was found to be stable for several hours of use when using elevated carrier gas pressures (90 psi) and a small restriction (25 μm I.D. tubing) at the outlet. This normally provided good performance at temperatures up to about 200 °C with very little background interference in the FID. Given its separation properties, a short 2 m × 100 μm I.D. column was found to be preferable for most separations in this study. Measurements indicated the coating procedure yielded a sulfolane film near 4 μm thick on this column, which produced 4400 plates for benzene with a sample capacity near 30 μg. The sulfolane phase yielded good retention and peak shape for many analytes including alkanes, aromatics, alcohols, bases, sulfides, phosphites, thiols, and others. Compared to longer conventional GC columns, the relatively short sulfolane column was found to offer improved selectivity in the separation of unsaturated, aromatic, and alkane test analytes. As such the method was successfully applied to the analysis of aromatics in gasoline headspace. Results suggest that sulfolane could be a potentially useful stationary phase to further explore in GC separations.

Determination of vacuum ultraviolet detector response factors by hyphenation with two-dimensional comprehensive gas chromatography with flame ionization detection

Two-dimensional comprehensive gas chromatography is an established technique, employed for the characterization of complex samples. Broadband vacuum ultraviolet absorption spectroscopy detection has recently attracted a lot of attention as it is a universal detection technique characterized by good selectivity but also ease of use and amenability to coupling with two-dimensional comprehensive gas chromatography. Vacuum ultraviolet spectroscopy is particularly interesting due to the possibility of performing spectral decomposition for species that coelute in gas chromatography analysis. This detector has quantitative capabilities, however not all species absorb vacuum ultraviolet radiation the same. Unfortunately, vacuum ultraviolet relative response factors for compounds are not always available. Methods to rapidly measure vacuum ultraviolet relative response factors and generate a large database that would allow calibration free quantitative analysis of complex mixtures are therefore of great interest. In this work, a universal methodology that permits rapid measurement of vacuum ultraviolet relative response factors is reported. It involves flow modulated two-dimensional comprehensive gas chromatography with dual vacuum ultraviolet and flame ionization detection. In this set-up, flame ionization detection is employed as a quantitative reference allowing to scale vacuum ultraviolet responses of investigated compounds. This approach was validated by flow measurements and by comparing relative response factors obtained for model compounds with literature data.

High-Sensitivity Raman Gas Probe for In Situ Multi-Component Gas Detection

Multiple reflection has been proven to be an effective method to enhance the gas detection sensitivity of Raman spectroscopy, while Raman gas probes based on the multiple reflection principle have been rarely reported on. In this paper, a multi-reflection, cavity enhanced Raman spectroscopy (CERS) probe was developed and used for in situ multi-component gas detection. Owing to signal transmission through optical fibers and the miniaturization of multi-reflection cavity, the CERS probe exhibited the advantages of in situ detection and higher detection sensitivity. Compared with the conventional, backscattering Raman layout, the CERS probe showed a better performance for the detection of weak signals with a relatively lower background. According to the 3σ criteria, the detection limits of this CERS probe for methane, hydrogen, carbon dioxide and water vapor are calculated to be 44.5 ppm, 192.9 ppm, 317.5 ppm and 0.67%, respectively. The results presented the development of this CERS probe as having great potential to provide a new method for industrial, multi-component online gas detection.

Comprehensive Screening of Polycyclic Aromatic Hydrocarbons and Similar Compounds Using GC-APLI-TIMS-TOFMS/GC-EI-MS

In the present work, a novel workflow based on complementary gas-phase separations for the identification of isomeric PAHs from complex mixtures is described. This is the first report on the coupling of gas chromatography (GC), atmospheric pressure laser ionization (APLI), and trapped ion mobility spectrometry-mass spectrometry (TIMS-MS) for the characterization of polycyclic aromatic hydrocarbons. Over a hundred known unknowns are uniquely identified based on the molecular ion retention indices I (5%), mobility (RSD < 0.6% and R = 50-90 with S_r = 0.18 V/ms), mobility-based theoretical candidate assignment (<3%), accurate mass chemical formula assignment (<2 ppm), and electron impact fragmentation pattern and database search. The advantages of theoretical modeling of PAHs and similar compounds were evaluated using candidate structures ranked by retention indices and fragmentation pattern from GC-EI-MS data sets. Over 20 PAH isomeric and deuterated standards were utilized for the GC-APLI-TIMS-TOF MS workflow validation. Noteworthy is the analytical capability for untargeted screening of isomeric and isobaric compounds with additional characterization metrics not available in traditional GC-EI-MSⁿ workflows.

A unique data analysis framework and open source benchmark data set for the analysis of comprehensive two-dimensional gas chromatography software

Comprehensive two-dimensional gas chromatography (GC × GC) is amongst the most powerful separation technologies currently existing. Since its advent in early 1990, it has become an established method which is readily available. However, one of its most challenging aspects, especially in hyphenation with mass spectrometry is the high amount of chemical information it provides for each measurement. The GC × GC community agrees that there, the highest demand for action is found. In response, the number of software packages allowing for in-depth data processing of GC × GC data has risen over the last couple of years. These packages provide sophisticated tools and algorithms allowing for more streamlined data evaluation. However, these tools/algorithms and their respective specific functionalities differ drastically within the available software packages and might result in various levels of findings if not appropriately implemented by the end users. This study focuses on two main objectives. First, to propose a data analysis framework and second to propose an open-source dataset for benchmarking software options and their specificities. Thus, allowing for an unanimous and comprehensive evaluation of GC × GC software. Thereby, the benchmark data includes a set of standard compound measurements and a set of chocolate aroma profiles. On this foundation, eight readily available GC × GC software packages were anonymously investigated for fundamental and advanced functionalities such as retention and detection device derived parameters, revealing differences in the determination of e.g. retention times and mass spectra.

Automating and Extending Comprehensive Two-Dimensional Gas Chromatography Data Processing by Interfacing Open-Source and Commercial Software

Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful analytical tool for both nontargeted and targeted analyses. However, there is a need for more integrated workflows for processing and managing the resultant high-complexity datasets. End-to-end workflows for processing GC×GC data are challenging and often require multiple tools or software to process a single dataset. We describe a new approach, which uses an existing underutilized interface within commercial software to integrate free and open-source/external scripts and tools, tailoring the workflow to the needs of the individual researcher within a single software environment. To demonstrate the concept, the interface was successfully used to complete a first-pass alignment on a large-scale GC×GC metabolomics dataset. The analysis was performed by interfacing bespoke and published external algorithms within a commercial software environment to automatically correct the variation in retention times captured by a routine reference standard. Variation in ¹t_R and ²t_R was reduced on average from 8 and 16% CV prealignment to less than 1 and 2% post alignment, respectively. The interface enables automation and creation of new functions and increases the interconnectivity between chemometric tools, providing a window for integrating data-processing software with larger informatics-based data management platforms.

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.

Simultaneous Quantification of Multiple Polycyclic Aromatic Hydrocarbons in Aqueous Media using Micelle Assisted White Light Excitation Fluorescence

Qualitative and quantitative display of multiple fluorescent analytes is made simple and reliable in this micelle assisted methodology. The adopted method involves micelle assisted evincing of ppb level of PAHs in water; measurement of total fluorescence (white light excitation fluorescence, WLEF) and data deciphering using multivariate analysis. This protocol yields sensitive and accurate quantification of the cancerous pollutants (PAHs) in aqueous media with Limit of Quantification of the order 1-10 μg/L and accuracy of >98%. The use of WLEF enables the simultaneous acquisition of fluorescence signatures of all the PAHs. It has the additional advantage of being portable, layman-friendly and cost-effective. The optimized amount of surfactants for the simultaneous extraction of PAHs from real samples was estimated as 27.8 mg (19.3 mM) of SDS and 9.1 mg (5 mM) of CTAB. Also, the analytical fidelity of the quantification such as percentage recovery (98 ± 2%), linear dynamic range (2-250 μg/L), RMSEP (<0.5), etc. explains the veracity of methodology.

Gas chromatography vacuum ultraviolet spectroscopy: A review

Accelerated technological progress and increased complexity of interrogated matrices imposes a demand for fast, powerful, and resolutive analysis techniques. Gas chromatography has been for a long time a 'go-to' technique for the analysis of mixtures of volatile and semi-volatile compounds. Coupling of the several dimensions of gas chromatography separation has allowed to access a realm of improved separations in the terms of increased separation power and detection sensitivity. Especially comprehensive separations offer an insight into detailed sample composition for complex samples. Combining these advanced separation techniques with an informative detection system such as vacuum ultraviolet spectroscopy is therefore of great interest. Almost all molecules absorb the vacuum ultraviolet radiation and have distinct spectral features with compound classes exhibiting spectral signature similarities. Spectral information can be 'filtered' to extract the response in the most informative spectral ranges. Developed algorithms allow spectral mixture estimation of coeluting species. Vacuum ultraviolet detector follows Beer-Lambert law, with the possibility of calibrationless quantitation. The purpose of this article is to provide an overview of the features and specificities of gas chromatography-vacuum ultraviolet spectroscopy coupling which has gained interest since the recent introduction of a commercial vacuum ultraviolet detector. Potentials and limitations, relevant theoretical considerations, recent advances and applications are explored.

Compositional Analysis of Heavy Petroleum Distillates by Comprehensive Two-dimensional Gas Chromatography, Field Ionization and High-resolution Mass Spectrometry

We report recent progresses of combining comprehensive two-dimensional gas chromatography (2DGC or GC × GC) separation, field ionization (FI), and time-of-flight mass spectrometry (TOF MS) for the detailed analysis of vacuum gas oil distillation (VGO) cuts. 2DGC separates petroleum molecules by the combination of boiling point and polarity. FI generates molecule ions-only mass spectra. TOF MS allows accurate mass analysis of hydrocarbon molecules. A new data analysis strategy is implemented for compositional analysis. First, all masses were separated into nominal mass classes. Since petroleum homologues have unique Kendrick mass defects (KMD), KMD plots were generated for easy recognition of homologues series within each nominal mass class. Finally, KMD windows were imposed for complete resolution of petroleum molecules. Using this approach, a total of 16 hydrocarbon types, 14 sulfur types, and their carbon number distributions were determined in the three VGO distillation cuts. Two series of geological biomarkers were also revealed by the analysis.

Less than one minute low-pressure gas chromatography - mass spectrometry

Conventional gas chromatography - mass spectrometry (GC-MS) takes 20-40 min per sample, which is undesirably slow in any application if speed can be increased while still meeting analytical needs. In this study, we achieved reasonably good separations with full analysis cycle times of less than 1 min by combining for the first time low-pressure (LP) GC-MS with low thermal mass (LTM) resistive-heating for rapid temperature ramping and cooling of the capillary column. The analytical column is threaded into the LTM thin-walled metal tubing in an instrumental device known as "LTM Fast GC" that is mounted at the top of the gas chromatograph in a detector port. The column inlet and outlet are connected to the GC injector and MS transfer line as usual. For LPGC-MS, a 40 cm, 0.1 mm. i.d. uncoated flow restrictor capillary connected at the injector is coupled with a 2.6 m, 0.25 mm i.d., 0.25 µm film thickness analytical column leading to the MS. Thus, the inlet operates at normal GC pressures, but the analytical column is under vacuum, which increases the optimal helium carrier gas flow velocity thereby increasing speed of full range separations while maintaining acceptable quality of chromatography. This column configuration in LTM-LPGC-MS trades a 64-fold gain in speed of analysis vs. standard GC-MS for a 4-fold loss in chromatographic peak capacity, thereby converting analysis time from minutes into seconds in common applications. For example, jet fuel containing fatty acid methyl esters (akin to biofuel) was separated in 25 s with <1 min full analysis cycle time. An EPA Method 8270 mixture of 76 analytes was also analyzed in <1 min full cycle time by LTM-LPGC-MS. Other examples include very fast analysis of heroin in a street drug powder and elucidation of a new organic synthetic compound. In this report, we describe and discuss the several advantageous and practical features of LTM-LPGC-MS, as well as its trade-offs.

Star-poly(ε-caprolactone) as the stationary phase for capillary gas chromatographic separation

This work presents the separation performance of star-poly(ε-caprolactone) (star-PCL) as the stationary phase for capillary gas chromatography (GC). The statically coated star-PCL column showed a column efficiency of 3345 plates per m and moderate polarity. Importantly, the star-PCL column exhibited high selectivity and resolving capability for more than a dozen mixtures covering a wide-ranging variety of analytes and isomers. Among them, the star-PCL column displayed advantageous resolving capability over the commercial DB-1701 column for aromatic amine isomers such as toluidine, chloroaniline and bromoaniline. Moreover, it was applied for the determination of isomer impurities in real samples, showing good potential in GC applications.

"-Omics" workflow for paleolimnological and geological archives: A review

"-Omics" is a powerful screening method with applications in molecular biology, toxicology, wildlife biology, natural product discovery, and many other fields. Genomics, proteomics, metabolomics, and lipidomics are common examples included under the "-omics" umbrella. This screening method uses combinations of untargeted, semi-targeted, and targeted analyses paired with data mining to facilitate researchers' understanding of the genome, proteins, and small organic molecules in biological systems. Recently, however, the use of "-omics" has expanded into the fields of geology, specifically petrology, and paleolimnology. Specifically, untargeted analyses stand to transform these fields as petroleomics, and sediment-"omics" become more prevalent. "-Omics" facilitates the visualization of small molecule profiles from environmental matrices (i.e. oil and sediment). Small molecule profiles can provide improved understanding of small molecules distributions throughout the environment, and how those compositions can change depending on conditions (i.e. climate change, weathering, etc.). "-Omics" also facilities discovery of next-generation biomarkers that can be used for oil source identification and as proxies for reconstructing past environmental changes. Untargeted analyses paired with data mining and multivariate statistical analyses represents a powerful suite of tools for hypothesis generation, and new method development for environmental reconstructions. Here we present an introduction to "-omics" methodology, technical terms, and examples of applications to paleolimnology and petrology. The purpose of this review is to highlight the important considerations at each step in the "-omics" workflow to produce high quality and statistically powerful data for petrological and paleolimnological applications.

p-Nitro-tetradecyloxy-calix[4]arene as a highly selective stationary phase for gas chromatographic separations

Here, we report the first example of the utilization of p-nitro-tetradecyloxy-calix[4]arene (C4A-NO₂) as a stationary phase for capillary gas chromatographic (GC) separations.