Comprehensive Gas Chromatography-mass Spectrometry Research Articles

Analysis of pyrolysis liquids from scrap tires using comprehensive gas chromatography–mass spectrometry and unsupervised learning

During the pyrolysis of scrap tires a complex mixtures of organic compounds is liberated and can be condensed as liquid product. In this study comprehensive gas chromatography–mass spectrometry (GC×GC–MS) and headspace gas chromatography (HS-GC) are used to unravel the complex nature of pyrolysis liquids from scrap tires produced by means of an inductively heated batch reactor. Two strategies were employed. On the one hand a set of reference compounds was used for quantification, on the other hand unsupervised learning (c-means clustering) was used to deduce compound classes and assignment of compound class structural features from MS data. The clustering finally allowed the evaluation of the influence of time and heating rate on observable peak areas. It could be shown, that peak area of saturated and partially unsaturated (hydroaromatic) compounds decreased during the time course of experiments and with increasing heating rate, whereas aromatic compounds increased during the course and were favorably liberated at high heating rates.

Diaromatic sulphur-containing ‘naphthenic’ acids in process waters

Polar organic compounds found in industrial process waters, particularly those originating from biodegraded petroleum residues, include ‘naphthenic acids’ (NA). Some NA have been shown to have acute toxicity to fish and also to produce sub-lethal effects. Whilst some of these toxic effects are produced by identifiable carboxylic acids, acids such as sulphur-containing acids, which have been detected, but not yet identified, may produce others. Therefore, in the present study, the sulphur-containing acids in oil sands process water were studied.A fraction (ca 12% by weight of the total NA containing ca 1.5% weight sulphur) was obtained by elution of methylated NA through an argentation solid phase extraction column with diethyl ether. This was examined by multidimensional comprehensive gas chromatography-mass spectrometry (GCxGC-MS) in both nominal and high resolution mass accuracy modes and by GCxGC-sulphur chemiluminescence detection (GCxGC-SCD).Interpretation of the mass spectra and retention behaviour of methyl esters of several synthesised sulphur acids and the unknowns allowed delimitation of the structures, but not complete identification. Diaromatic sulphur-containing alkanoic acids were suggested.Computer modelling of the toxicities of some of the possible acids suggested they would have similar toxicities to one another and to dehydroabietic acid. However, the sulphur-rich fraction was not toxic or estrogenic to trout hepatocytes, suggesting the concentrations of sulphur acids in this sample were too low to produce any such effects in vitro. Further samples should probably be examined for these compounds.

High concentration capacity sample preparation techniques to improve the informative potential of two-dimensional comprehensive gas chromatography–mass spectrometry: Application to sensomics

This study reports and critically discusses the results of a systematic investigation on the effectiveness of different and complementary sampling approaches, based on either sorption and adsorption, treated as a further dimension of a two-dimensional comprehensive gas chromatography–mass spectrometry analytical platform for sensomics. The focus is on the potentials of a group of high concentration capacity (HCC) sample preparation (Solid Phase Microextraction, SPME, Stir Bar Sorptive Extraction, SBSE and Headspace Sorptive Extraction, HSSE) and Dynamic Headspace (D-HS) techniques investigated to provide information useful for fingerprinting and profiling studies of food aroma. Volatiles and semi-volatiles contributing to define whole and nonfat dry milk aroma have been successfully characterized thanks to the combination of effective and selective sampling by HCC and D-HS techniques, high separation and detection power of GC×GC–MS and suitable data elaboration (i.e., Comprehensive Template Matching Fingerprinting – CTMF). Out of the sample preparation techniques investigated, HSSE and SBSE have shown to be really effective for sensomics studies because of their high concentration factors, providing highly representative profiles as well as analyte recovery suitable for GC-Olfactometry even with high odor threshold (OT) markers or potent odorants in sub-trace amounts.

Quantitative fingerprinting by headspace—Two-dimensional comprehensive gas chromatography–mass spectrometry of solid matrices: Some challenging aspects of the exhaustive assessment of food volatiles

The study proposes an investigation strategy that simultaneously provides detailed profiling and quantitative fingerprinting of food volatiles, through a “comprehensive” analytical platform that includes sample preparation by Headspace Solid Phase Microextraction (HS-SPME), separation by two-dimensional comprehensive gas chromatography coupled with mass spectrometry detection (GC×GC–MS) and data processing using advanced fingerprinting approaches.Experiments were carried out on roasted hazelnuts and on Gianduja pastes (sugar, vegetable oil, hazelnuts, cocoa, nonfat dried milk, vanilla flavorings) and demonstrated that the information potential of each analysis can better be exploited if suitable quantitation methods are applied. Quantitation approaches through Multiple Headspace Extraction and Standard Addition were compared in terms of performance parameters (linearity, precision, accuracy, Limit of Detection and Limit of Quantitation) under headspace linearity conditions. The results on 19 key analytes, potent odorants, and technological markers, and more than 300 fingerprint components, were used for further processing to obtain information concerning the effect of the matrix on volatile release, and to produce an informative chemical blueprint for use in sensomics and flavoromics. The importance of quantitation approaches in headspace analysis of solid matrices of complex composition, and the advantages of MHE, are also critically discussed.

Different headspace solid phase microextraction – Gas chromatography/mass spectrometry approaches to haloanisoles analysis in wine

Three approaches in determination of six haloanisoles (2,4,6-trichloroanisole, 2,3,4-trichloroanisole, 2,3,6-trichloroanisole, tetrachloroanisole, pentachloroanisole and 2,4,6-tribromoanisole) in wine were compared. Comprehensive gas chromatography – time of flight mass spectrometry (GC×GC–ToF-MS) was described for the first time for this application and compared to gas chromatography–tandem mass spectrometry (GC–MS/MS) using triple quadrupole instrument. These techniques were compared with “standard” analytical approach using GC–MS(SIM). SPME method was developed and used for all separation methods (DVB/PDMS fiber, 70°C, 30%NaCl, 20min extraction). Extraction dependence on matrix was discussed using model wines with different ethanol contents (8%, 12%, and 18%) as well as water and different wines (dry white, dry red and sweet liqueur), with the lowest sensitivities obtained for highest ethanol contents in model wine and for liqueur wine. Limits of detection for GC×GC–ToF-MS method were 0.09–2.92ng/L depending on the examined compound and matrix (compared to 0.1–13.3ng/L obtained using GC/MS(SIM)). For GC–MS/MS method lower detection limits were achieved than for the GC×GC method (0.01–0.1ng/L), however comprehensive gas chromatography-mass spectrometry provides full spectral information on analyzed compounds. Both methods had limits of detection far below odor thresholds of haloanisoles in wine, good linearity up to 2000ng/L tested and good precision, what makes them suitable for analysis of these compounds in low ppt levels.

Classification of chemical compound classes in slow pyrolysis liquids from brown coal using comprehensive gas-chromatography mass-spectrometry

The depletion of fossil fuels like crude oil or natural gas in foreseeable future urges the search for alternative fuels. Alternative resources for the production of fuels are biomass or coal, which have already been the feedstock for the chemical industry decades ago. One way for the production of fuels from theses feedstocks is pyrolysis and current research focuses on the influence of process parameters on composition of liquids from pyrolysis and the optimization of the properties necessary for the proposed utilization. To unravel the chemical composition of these oils, high performance instrumental analytical methods like comprehensive gas-chromatography mass-spectrometry (GC×GC–MS) are highly beneficial. Unfortunately obtained data sets are very complex and dedicated interpretation methods are needed. In this study, the classification of about thousand compounds in a GC×GC–MS chromatogram of a brown coal pyrolysis oil is demonstrated by means of linear discriminant analysis. Based on a reference compound training set, the compound classes alkanes, alkenes, thiophenes, and benzothiophenes could be assigned with low classification error. This will help in the understanding of the influence of process parameters and feedstocks on the composition of pyrolysis oils.

Determination of compounds responsible for tempeh aroma

Tempeh is a fermented food, popular mainly in south-east Asia, but also among vegetarians worldwide. It is produced by fermenting soybean or other beans with Rhizopus strains and usually eaten deep-fried, steamed or roasted. The flavour of tempeh depends upon the fermentation time, beans used and the (eventual) frying process. Our goal was to identify compounds responsible for the unique aroma of fermented and fried soy tempeh. Gas chromatography–olfactometry (GC–O) with the aroma extract dilution analysis (AEDA) approach, was used to determine key odorants after 1 and 5days of fermentation and subsequent frying. Comprehensive gas chromatography–mass spectrometry (GC×GC–ToF-MS) was used for their quantitation using stable isotope dilution analysis (SIDA) or standard addition (SA) methods. Odour activity values (OAV) were calculated for 19 out of 21 key odorants. Tempeh was fermented for 5days and fried, and the main aroma compounds were found to be the following: 2-acetyl-1-pyrroline, (FD=1024, OAV 1380), 2-ethyl-3,5-dimethylpyrazine (FD=512, OAV 338), dimethyl trisulfide, (FD=512, OAV 900), methional (FD=512, OAV 930), 2-methylpropanal (FD=512, OAV 311) and (E,E)-2,4-decadienal (FD=512, OAV 455). The frying process induced the increase or appearance of the main key odorants in tempeh.

Isolation and estimation of the ‘aromatic’ naphthenic acid content of an oil sands process-affected water extract

The naphthenic acids of oil sands process-affected water (OSPW) are said to be important toxicants. The major acids are stated to have alicyclic structures and recently, numerous of these have been identified, but some evidence suggests ‘aromatic’ acids are also present. The proportions of such acids have not been reported because they exist in so-called supercomplex mixtures with the alicyclic species. Their contribution to the toxicity of OSPW, if any, is therefore unknown. Here we report the use of multidimensional comprehensive gas chromatography–mass spectrometry (GC×GC–MS) with polar first dimension and non-polar second dimension GC columns and argentation solid phase extraction, to separate methyl esters of the acids of an OSPW supercomplex, into distinct fractions. A major fraction (ca 70%) was shown to contain acids (methyl esters) previously identified as alicyclic species. Authentic adamantane acid methyl esters were shown to chromatograph in this fraction. This fraction was isolated by argentation solid phase extraction (SPE) by elution with hexane. GC–MS and GC×GC–MS confirmed this to be the major fraction in the original supercomplex containing alicyclic acids (methyl esters). A second fraction shown to contain monoaromatic acids (methyl esters) by GC×GC–MS was unexpectedly abundant (ca 30% relative to the acyclic acids). The naphtheno-aromatic dehydroabietic acid was confirmed by co-injection with an authentic compound and several acids previously tentatively identified as naphtheno-monoaromatics were present. This fraction was isolated by argentation SPE by elution with more polar 5% diethyl ether in hexane. GC–MS and GC×GC–MS confirmed that the fraction represented a significant proportion of the original supercomplex. A further fraction, eluting from the argentation SPE column with more 5% diethyl ether in hexane in the same retention volume as authentic methyl naphthoate, contained, in addition to some of the second fraction, a third, much more minor complex. This had somewhat similar GC×GC retention characteristics to that of methyl naphthoate and the methyl ester of authentic fluorene-9-carboxylic acid. Spectra are reported. Non-alicyclic, mono- and possibly diaromatic acids are a much more quantitatively significant proportion of OSPW than previously realised. The individual acids need to be better identified and the toxicity of these and other SPE fractions studied in order to assess any possible environmental effects of OSPW.

A flow-modulated comprehensive gas chromatography–mass spectrometry method for the analysis of fatty acid profiles in marine and biological samples

The present investigation is focused on the development of a flow-modulator (FM) comprehensive 2D GC (GC×GC)-quadrupole mass spectrometry (qMS) approach, for the analysis of fatty acids. A recently developed flow modulator interfaced an apolar–polar column set, and was used for the first time with a mass spectrometer. Method development was achieved by using a standard mixture, containing fatty acid methyl esters (FAMEs). The total run time was approx. 40min, thus relatively rapid. The optimized FM GC×GC–qMS method was applied to marine and biological FAMEs. Validation parameters such as intra-day and inter-day repeatability, limits of identification (mass spectral quality was evaluated at various FAME concentrations), and quantification were measured. Peak assignment was performed using pure standard compounds (when available), linear retention indices (LRIs), a dedicated FAME MS database, and specific bidimensional chromatogram positions. The MS database contained one-dimensional LRI information, exploited as a filter during the MS database search procedure. A good agreement was observed between database LRI values, and those calculated on the twin-column set. The FM GC×GC–qMS method can be considered as a valid counterpart, with respect to cryogenically modulated GC×GC, in the fatty acid field of research.

Extractive ethoxycarbonylation in high-temperature gas chromatography–mass spectrometry based analysis of serum estrogens

A comprehensive gas chromatography–mass spectrometry (GC–MS)-based profiling was developed as a practical assay for quantification of 18 endogenous estrogens in serum samples. The present GC–MS method was conducted with the two-phase extractive ethoxycarbonlyation (EOC) of the phenolic hydroxy groups of estrogen with ethyl chlorformate combined with the non-polar n-hexane extraction. The subsequent perfluoroacylation of aliphatic hydroxy groups with pentafluoropropionyl anhydride (PFPA) was conducted. The serum samples were separated through a high temperature GC column (MXT-1) within an 8-min run and analyzed in selected-ion monitoring mode with good chromatographic properties for 18 estrogens as their EOC-PFP derivatives. The limit of quantification (LOQ) was 0.025–0.10 ng/mL for most estrogens analyzed except for E3 and 2-OH-E3 (0.5 ng/mL each). The devised method was found to be linear over a 10 3-fold concentration range with a correlation coefficient ( r 2 > 0.992), whereas the precision (% CV) and accuracy (% bias) ranged from 3.1 to 16.3% and from 93.5 to 111.1%, respectively. Decreased 2-methoxy-17β-estradiol levels were confirmed in patients with preeclampsia than healthy pregnant women. This technique can be used for a clinical diagnosis as well as understanding the pathogenesis in estrogen-related disorders.

Steroidal Aromatic ‘Naphthenic Acids’ in Oil Sands Process-Affected Water: Structural Comparisons with Environmental Estrogens

The large volumes, acute toxicity, estrogenicity, and antiandrogenicity of process-affected waters accruing in tailings ponds from the operations of the Alberta oil sands industries pose a significant task for environmental reclamation. Synchronous fluorescence spectra (SFS) suggest that oil sands process-affected water (OSPW) may contain aromatic carboxylic acids, which are among the potentially environmentally important toxicants, but no such acids have yet been identified, limiting interpretations of the results of estrogenicity and other assays. Here we show that multidimensional comprehensive gas chromatography-mass spectrometry (GCxGC-MS) of methyl esters of acids in an OSPW sample produces mass spectra consistent with their assignment as C(19) and C(20) C-ring monoaromatic hydroxy steroid acids, D-ring opened hydroxy and nonhydroxy polyhydrophenanthroic acids with one aromatic and two alicyclic rings and A-ring opened steroidal keto acids. High resolution MS data support the assignment of several of the so-called 'O3' species. When fractions of distilled, esterified, OSPW acid-extractable organics were examined, the putative aromatics were mainly present in a high boiling fraction; when examined by argentation thin layer chromatography, some were present in a fraction with a retardation factor between that of the methyl esters of synthetic monoalicyclic and monoaromatic acids. Ultraviolet absorption spectra of these fractions indicated the presence of benzenoid moieties. SFS of model octahydro- and tetrahydrophenanthroic acids produced emissions at the characteristic excitation wavelengths observed in some OSPW extracts, consistent with the postulations from ultraviolet spectroscopy and mass spectrometry data. We suggest the acids originate from extensive biodegradation of C-ring monoaromatic steroid hydrocarbons and offer a means of differentiating residues at different biodegradation stages in tailings ponds. Structural similarities with estrone and estradiol imply that such compounds may account for some of the environmental estrogenic activity reported in OSPW acid-extractable organics and naphthenic acids.

Compositional heterogeneity may limit the usefulness of some commercial naphthenic acids for toxicity assays

Naphthenic acids are considered variously as monocarboxylic acids fitting the formula C nH 2n + z O 2 (where z is a zero or negative even integer), as only alicyclic ( i.e. non-aromatic) monocarboxylic acids fitting this formula (z ≤ 0), or simply as those carboxylic acids occurring in petroleum products or crude oils that have been formed through biodegradation of hydrocarbons. Such acids are known constituents of the process-affected water associated with some expanding oil sands industries, of some immature and biodegraded crude oils, of produced water discharges from oil production platforms and are used as biocides and as components in the manufacture of steel radial tyres. As a result of these potential vectors of the acids into the environment, various naphthenic acid mixtures which are available commercially have been used for a range of toxicity studies. However, as some manufacturers make clear, but which is not often emphasised in the toxicity studies, a range of different quality naphthenic acids is produced commercially. It has been suggested previously, and we showed recently and elucidate further herein, that such commercial mixtures therefore sometimes contain toxic components other than carboxylic acids. For example, we identify herein by two-dimensional comprehensive gas chromatography–mass spectrometry, a range of C 0–6 alkylphenols in a batch of commercial naphthenic acids. Since these compounds are known toxicants, the contribution of such non-carboxylic acids, if any, to the toxicity attributed previously to the acids, should also be considered. This will be reflected in the concentrations and effective toxicities of such components. In order to establish the toxicity of the acids per se, assays of pure synthetic carboxylic acids of the type now known to be present in naphthenic acids from petroleum or oil sands may be more appropriate than tests of the toxicity of largely unknown, heterogeneous, mixtures.

Monocyclic and monoaromatic naphthenic acids: synthesis and characterisation

Characterisation of the complex mixtures of carboxylic acids (naphthenic acids) occurring in crude oils and in degraded oil sands is environmentally important. Indeed some acids in waters from oil platforms are apparently hormonally active, and the oil sands acids are said to be toxic to a wide range of biota. Previous attempts to identify monocyclic and monoaromatic naphthenic acids have been hampered by the lack of authenticated synthetic reference compounds. Some studies have indicated that acids with ethanoic acid side chains are present in the naphthenic acids mixtures, so in the present study, we synthesised and characterised by mass spectrometry, a range (C8–14) of monoaromatic and monocyclic ethanoic acids. Using 2-D comprehensive gas chromatography–mass spectrometry, we then compared the retention times and mass spectra of the synthetic acids with those of a commercial naphthenic acids mixture. Some alicyclic and numerous aromatic acids were successfully identified.

Diamonds in the Rough: Identification of Individual Naphthenic Acids in Oil Sands Process Water

Expansion of the oil sands industry of Canada has seen a concomitant increase in the amount of process water produced and stored in large lagoons known as tailings ponds. Concerns have been raised, particularly about the toxic complex mixtures of water-soluble naphthenic acids (NA) in the process water. To date, no individual NA have been identified, despite numerous attempts, and while the toxicity of broad classes of acids is of interest, toxicity is often structure-specific, so identification of individual acids may also be very important. Here we describe the chromatographic resolution and mass spectral identification of some individual NA from oil sands process water. We conclude that the presence of tricyclic diamondoid acids, never before even considered as NA, suggests an unprecedented degree of biodegradation of some of the oil in the oil sands. The identifications reported should now be followed by quantitative studies, and these used to direct toxicity assays of relevant NA and the method used to identify further NA to establish which, or whether all NA, are toxic. The two-dimensional comprehensive gas chromatography-mass spectrometry method described may also be important for helping to better focus reclamation/remediation strategies for NA as well as in facilitating the identification of the sources of NA in contaminated surface waters.

Identification, characterization and quantitation of pyrogenic polycylic aromatic hydrocarbons and other organic compounds in tire fire products

On 15 August 2001, a tire fire took place at the Pneu Lavoie Facility in Gatineau, Quebec, in which 4000 to 6000 new and recycled tires were stored along with other potentially hazardous materials. Comprehensive gas chromatography–mass spectrometry (GC–MS) analyses were performed on the tire fire samples to facilitate detailed chemical composition characterization of toxic polycyclic aromatic hydrocarbons (PAHs) and other organic compounds in samples. It is found that significant amounts of PAHs, particularly the high-ring-number PAHs, were generated during the fire. In total, 165 PAH compounds including 13 isomers of molecular weight (MW) 302, 10 isomers of MW 278, 10 isomers of MW 276, 7 isomers of MW 252, 7 isomers of MW 228, and 8 isomers of MW 216 PAHs were positively identified in the tire fire wipe samples for the first time. Numerous S-, O-, and N-containing PAH compounds were also detected. The identification and characterization of the PAH isomers was mainly based on: (1) a positive match of mass spectral data of the PAH isomers with the NIST authentic mass spectra database; (2) a positive match of the GC retention indices ( I) of PAHs with authentic standards and with those reported in the literature; (3) agreement of the PAH elution order with the NIST (US National Institute of Standards and Technology) Standard Reference Material 1597 for complex mixture of PAHs from coal tar; (4) a positive match of the distribution patterns of PAH isomers in the SIM mode between the tire fire samples and the NIST Standard Reference Materials and well-characterized reference oils. Quantitation of target PAHs was done on the GC–MS in the selected ion monitoring (SIM) mode using the internal standard method. The relative response factors (RRF) for target PAHs were obtained from analyses of authentic PAH standard compounds. Alkylated PAH homologues were quantitated using straight baseline integration of each level of alkylation.