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Vacuum‐assisted headspace solid‐phase microextraction (Vac‐HS‐SPME) is a technique used to enhance SPME sampling of semi‐volatile organic compounds. Here, it was combined with a high‐capacity SPME Arrow, which features a larger volume of extraction phase and a more rugged configuration than traditional extraction fibers. An in‐depth assessment of the critical parameters was conducted to achieve optimal extraction of representative compounds from a model solid sample matrix (Ottawa sand). Operational fundamentals investigated included the types of seals needed to create a leak‐free environment under vacuum conditions; the magnitude of the vacuum applied and time needed to activate the Vac kinetics; order of sample vial preparation methods (VPMs); and other standard variables associated with extract analysis by gas chromatography‐mass spectrometry. When exploring the limits of sample VPMs, results indicated an ideal workflow requires the solid sample to be spiked before sealing the vial, allow the sample to rest overnight, then apply vacuum at a pressure of ‐677 mbar (out of ‐789 mbar maximum possible vacuum with pump and compressor used), exerted on the vial for 90 s. This work provides the necessary workflow for the optimization of Vac‐HS‐SPME sampling of analytes from solid matrices. [ABSTRACT FROM AUTHOR]

Numerous treatment modalities have been employed over the years to eradicate bacterial communities in industrial wastewater. Oxidizing agents and chemical additives, such as ozone, permanganate, glutaraldehyde, and chlorine, are effective in treating microbial contaminants that are typically found in domestic wastewater. However, the chemical complexity of water produced from fracking requires novel approaches, because the microbes have developed mechanisms to overcome typical disinfectants. In this work, we test the effectiveness of bacteriophages for the eradication of two model bacteria from produced water: Pseudomonas aeruginosa and Bacillus megaterium. These bacteria were grown in low salinity produced water and exposed to their corresponding phage. Overall, the total inactivation of the P. aeruginosa population was achieved, as well as the inactivation of B. megaterium. These promising results provide a potentially useful tool for bacterial elimination in overall PW treatment, at an industrial scale. Particularly, since phage treatment is a rapid and cost-effective alternative. Moreover, these results fall within the objectives proposed as part of the sustainable development goals adopted worldwide. [ABSTRACT FROM AUTHOR]

In the modern world, energy and fuels are of utmost importance. Rapid characterization of petroleum and other hydrocarbon‐based fuel is a well‐researched field. Gas chromatography has traditionally been used to separate the different species and characterize the chemical content in fuels. Ideally, every molecule would be separated and characterized, but due to the complexity of the petroleum matrix, many compounds coelute. With the help of different detectors, more information can be gained, but there does not exist a single detector that can unambiguously differentiate and identify every compound. Vacuum ultraviolet spectroscopy (VUV) is a relatively new detector that can alleviate many limitations of other detectors. Based on spectroscopic absorption, VUV detection can provide qualitative and quantitative information regarding the composition of different fuels. It also provides certain advantages, allowing the deconvolution of coeluting peaks and differentiation between constitutional isomers. VUV has been used to classify the range of chemical components in many diverse fuel samples. Here, the contributions of VUV detection to petrochemical analysis to date are reviewed. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing utilizes pressurized liquid typically consisting of water, proppants, and a multitude of chemical additives, in order to fracture petroliferous strata to extract natural gas and oil. In this process, a vast amount of wastewater is produced. This water is heavily contaminated, which renders it unusable outside of direct reuse, without extensive treatment being performed. Typically, various sophisticated analytical techniques are involved in the characterization of both waste and treated waters, increasing the cost and the complexity of the management efforts. The article discusses the constituents found in oilfield wastewater, the methods used to identify and quantify these constituents, and the present management methods. Additionally, we introduce total organic carbon and conductivity analyses as surrogate measurements of overall water quality. Total organic carbon and conductivity are established bulk measurements, which can be used to facilitate rapid decisions regarding the treatment and greater utilization of flowback and produced oilfield wastes. The application of the proposed surrogates could be used to streamline the current myriad of complex and expensive measurements. This would improve operational efficiency with respect to wastewater management in the energy sector. [ABSTRACT FROM AUTHOR]

Environmental concerns with unconventional oil and gas development are frequently centered on elevated water usage and the induction of seismic events during waste disposal. Reuse of produced water for subsequent production well stimulation can effectively address these concerns, but the variability among such samples must be well understood. Twenty-four samples of wastewater from unconventional oil and gas development were collected from south and west Texas to assess their variability and feasibility for direct reuse. Bulk metrics were collected, including total organic carbon, total nitrogen, as well as total dissolved and suspended solids. The profiles of pertinent inorganic constituents were also evaluated. Variations were not only seen between regions but also among samples collected from the same region. For example, the average total organic carbon for Eagle Ford samples collected was 700 ± 500 mg/L, while samples collected from the Permian Basin featured an average total organic carbon concentration of 600 ± 900 mg/L. The Permian Basin total organic carbon ranged from 38 to 2600 mg/L. The total dissolved solids levels had the same variability between regions, with an average value for Eagle Ford of 20,000 ± 10,000 mg/L and a Permian Basin value of 150,000 ± 40,000 mg/L. However, samples were more reproducible within a given region. Collectively, the data indicate that the direct reuse of raw produced water for subsequent production well development without treatment is not feasible based on the reported reuse thresholds. Unconventional development wastewater samples from the Permian Basin were also compared to produced water values from conventional oil and gas wells in the same region, as reported by the United States Geological Survey. Samples collected in the Permian Basin consistently demonstrated lower ionic strength compared to conventional produced water data. [ABSTRACT FROM AUTHOR]

The relationship between metal levels in the Olt River ecosystem in southern Romania (measured during 2018‒2019, with 1064 sediment and water samples) and daily climate data were explored to assess the need for targeted source identification and mitigation strategies. In 2018, there was a strong relationship between the sediment Pb, As, Cd, and Hg contents and temperature (r > 0.8, p < 0.001). Mercury in sediments had a positive correlation with precipitation, and Hg in the water correlated with minimum temperature in May 2018 (p < 0.01). In July 2019, heavy metals were positively correlated with precipitation and negatively correlated with temperature. According to nonsymmetrical correspondence analysis, the four climate parameters analyzed were linearly correlated with the frequency of metal detection (p < 0.001) in both years. The statistical analysis showed strong relationships between heavy metal levels and climatic factors and attributed the discrepancies in elemental concentrations between 2018 and 2019 to climate warming. [ABSTRACT FROM AUTHOR]

A novel method development (MD) approach was established to aid column selection for online supercritical fluid extraction-supercritical fluid chromatography-mass spectrometry (SFE-SFC-MS). An adapted stationary phase (SP) selection procedure was used to expand traditional SFC-MS screening by inclusion of an "Analyte-Plug Retention Test." This test enabled an early evaluation of "trapping" capability for a plug of targeted analytes on the SP. Using an SFE-simulation method, the on-line trapping of an SFE-based extract-plug was mimicked by trapping an SFC-based injection-plug under instrument conditions similar to an actual on-line extraction. Thirteen SPs were screened using the adapted MD procedure as part of the SFC-separation optimization in the development of an on-line SFE-SFC-MS extraction method for anabolic agents (AAS) in anti-doping testing. A cyano SP was chosen for further development, based on chromatographic separation potential and high plug-retention potential for targeted analytes. The chosen column was used in "proof-of-concept" on-line extractions using a generic SFE-SFC-MS method. Successful extract-plug trapping was demonstrated. Retention times and peak areas (4–20%RSD) were reproducible for targeted AAS. Successful first round SFE-SFC-MS SP selection was demonstrated to circumvent tedious re-optimization in future development stages and streamlining of the hyphenated SFE-SFC-MS MD process. [ABSTRACT FROM AUTHOR]

In the host, pathogenic microorganisms have developed stress responses to cope with constantly changing environments. Stress responses are directly related to changes in several metabolomic pathways, which could hamper microorganisms' unequivocal identification. We evaluated the effect of various in vitro stress conditions (acidic, basic, oxidative, ethanolic, and saline conditions) on the metabolism of Staphylococcus aureus, Bacillus cereus, and Pseudomonas aeruginosa, which are common lung pathogens. The metabolite profiles of the bacteria were analyzed using liquid chromatography coupled to triple quadrupole and quadrupole time-of-flight mass spectrometry. The advantages of targeted and untargeted analysis combined with univariate and multivariate statistical analysis (principal component analysis, hierarchical cluster analysis, partial least square discriminant analysis, random forest) were combined to unequivocally identify bacterial species. In normal in vitro conditions, the targeted methodology, based on the analysis of primary metabolites, enabled the rapid and efficient discrimination of the three bacteria. In changing in vitro conditions and specifically in presence of the various stressors, the untargeted methodology proved to be more valuable for the global and accurate differentiation of the three bacteria, also considering the type of stress environment within each species. In addition, species-specific metabolites (i.e., fatty acids, polysaccharides, peptides, and nucleotide bases derivatives) were putatively identified. Good intra-day repeatability and inter-day repeatability (< 10% RSD and < 15% RSD, respectively) were obtained for the targeted and the untargeted methods. This untargeted approach highlights its importance in unusual (and less known) bacterial growth environments, being a powerful tool for infectious disease diagnosis, where the accurate classification of microorganisms is sought. [ABSTRACT FROM AUTHOR]

Beer styles show wide variation in color, flavor, and clarity, due to differences in their chemical content. Some of the major flavor compounds in beer are isomerized alpha acids and phenolic compounds. These were investigated as potentially discerning features between beer styles. A selection of 32 American beers covering five styles was analyzed using liquid chromatography quadrupole time‐of‐flight mass spectrometry, which resulted in high mass accuracy chromatograms of the studied analytes. Distinctions between the presence or relative concentrations of certain compounds were observed and related back to brewing ingredients and procedures. For example, vanillin was only observed in stout beers due to the use of roasted barley malts for brewing, while chlorogenic acid isomers were found in two sours at relatively high concentrations (189 and 34 mg/L) because of the fruits used to flavor the beers. Distinctions were further confirmed using multivariate analysis techniques, which separated three of the five beer styles (India pale ales, stouts, and sours). [ABSTRACT FROM AUTHOR]

Per‐ and polyfluorinated alkyl substances are large class of man‐made compounds known in the media as "forever chemicals". In 2015, ASTM International published ASTM D7979, for the analysis of per‐ and polyfluorinated alkyl substances in non‐potable water samples. This method extracts the substances by co‐solvation with methanol and measures targeted compounds using liquid chromatography–tandem mass spectrometry. ASTM D7979 is a performance‐based method that analyzes 31 compounds plus 14 isotopically labeled surrogates. The minimum reporting limit is approximately 10 ng/L with an analytical range of 10–200 ng/L for most compounds. Expected recovery of surrogates and spiked matrices is 70–130%. Samples containing high suspended solids can be analyzed with minimal interferences and potential loss of analyte. The method is consistent with ASTM and EPA's sustainable development goals by using reduced volumes of sample, solvent, and minimizing hazardous solvents and sample preparation materials while maintaining data quality and detection limits that are suitable for the intended use. This paper covers the rationale, outlines some of the challenges associated with analysis of per‐ and polyfluorinated alkyl substances, and describes the steps taken by the ASTM Committee D19 task group to develop, optimize, and validate this method. [ABSTRACT FROM AUTHOR]

The analysis of proteins in biological samples is highly desirable, given their connection to myriad biological functions and disease states, as well as the growing interest in the development of protein‐based pharmaceuticals. The introduction and maturation of "soft" ionization methods, such as electrospray ionization and matrix‐assisted laser desorption/ionization, have made mass spectrometry an indispensable tool for the analysis of proteins. Despite the availability of powerful instrumentation, sample preparation and fractionation remain among the most challenging aspects of protein analysis. This review summarizes these challenges and provides an overview of the state‐of‐the‐art in sample preparation and fractionation of proteins for mass spectrometric analysis, with an emphasis on those used for top‐down proteomic approaches. Biological fluids, particularly important for clinical and pharmaceutical applications and their characteristics are also discussed. While immunoaffinity‐based methods are addressed, more attention is given to non‐immunoaffinity‐based methods, such as precipitation, coacervation, size exclusion, dialysis, solid‐phase extraction, and electrophoresis. These techniques are presented in the context of a significant number of studies where they have been developed and utilized. [ABSTRACT FROM AUTHOR]

Identifying bacterial species is essential to epidemiological surveillance. However, the determination of bacterial species is a tedious and labor‐intensive process. Various machine learning methods have been used for identifying bacterial species with mass spectral fingerprints. Although machine learning methods achieve real‐time identification without human experts, it still requires data preprocessing. To address this issue, we proposed a unified solution for the identification of bacterial species with a convolutional neural network. The neural network automatically determined species according to their mass spectra without the preprocessing steps. The convolutional and pooling layers in the neural network could replace the binning, baseline correction, and scaling procedures. Moreover, because of the explainable structure, the model could identify important regions of spectra to discriminate each bacterial species. We used spectral samples obtained from the fatty acid methyl esters of 10 samples from 16 bacterial species (a total of 16) to demonstrate the usefulness of the proposed method by comparing it with existing classification methods preceded by preprocessing. The comparison results confirmed that the proposed method outperformed the alternatives in terms of classification accuracy and robustness. Moreover, the classification results of the proposed method are interpretable. Identifying bacterial species is essential to epidemiological surveillance. However, the determination of bacterial species is labor‐intensive. Various machine learning methods have been used for identifying bacterial species with mass spectral fingerprints. Although machine learning methods achieve real‐time identification without human experts, it still requires data preprocessing. We proposed a unified solution for the identification of bacterial species with a convolutional neural network. The comparison results confirmed that the proposed method outperformed the alternatives in terms of classification accuracy and robustness. [ABSTRACT FROM AUTHOR]

The estimated global hard cider market is over $10 billion. Methods for determining their sugar content would have important implications in their quality assurance and nutritional values. In this study, the concentrations of fructose, glucose, and sucrose were determined in commercial hard cider and apple juice samples by hydrophilic interaction liquid chromatography with tandem mass spectrometry. The optimized sample preparation method consisted of sonication, a 1:10 dilution to 70:30 acetonitrile:water, centrifugation, filtration, and an additional 1:100 dilution to a final solvent composition of 80:20 acetonitrile:water. This method was validated with respect to selectivity, linearity, limit of detection, limit of quantitation, accuracy, and precision. Limits of detection and quantitation ranged from 0.01 to 0.1 and 0.05 to 0.5 mg/L, respectively, and linear ranges spanned at least a factor of 500 with excellent linearities (R2 > 0.999). Accuracy ranged from 81.7 to 107%. The relative standard deviations for all measurements were <7%. The method was applied to 11 different cider samples, one apple ale sample, and three different apple juice samples. Among the cider samples, a correlation between the fructose and glucose concentrations was found (R2 = 0.81). [ABSTRACT FROM AUTHOR]

The continued rise in the extraction of unconventional oil and gas across the globe poses many questions about how to manage these relatively new waste‐streams. Produced water, the primary waste by‐product, contains a diverse number of anthropogenic additives together with the numerous hydrocarbons extracted from the well. Due to potential environmental hazards, it is critical to characterize the chemical composition of this type of waste before proper disposal or remediation/reuse. In this work, a thin film solid phase microextraction approach was developed and optimized to characterize produced water. The thin film device consisted of hydrophilic‐lipophilic balance particles embedded in polydimethylsiloxane and immobilized on a carbon mesh surface. These devices were chosen to provide broad extraction coverage and high reusability. Various parameters were evaluated to ensure reproducible results while minimizing analyte loss. This optimized protocol, consisting of a 15 min extraction followed by a short (3 s) rinsing step, enabled the reproducible analysis of produced water without any sample pretreatment. Extraction efficiency was suitable for both produced water additives and hydrocarbons. The developed approach was able to tentatively identify a total of 201 compounds from produced water samples, by using one‐dimensional gas chromatography hyphenated to mass spectrometry and data deconvolution. [ABSTRACT FROM AUTHOR]

In biological systems, variable protein expression is a crucial marker for numerous diseases, including cancer. The vast majority of liquid chromatography–triple quadrupole mass spectrometry‐based quantitative protein assays use bottom‐up methodologies, where proteins are subjected to proteolytic cleavage prior to analysis. Here, the effect of difluoroacetic acid and biological matrices on the developement of a multiple reaction monitoring based top‐down reversed‐phase liquid chromatography–triple quadrupole mass spectrometry method for analysis of cancer‐related intact proteins was evaluated. Seven growth factors (5.5–26.5 kDa; isoelectric points: 4.6–9.9) were analyzed on a wide‐pore C4 column. The optimized method was performed at 30°C, using a 0.2 mL/min flow rate, a 10 %B/min gradient slope, and 0.05% v/v difluoroacetic acid as a mobile phase modifier. The increase of mass spectrometry sensitivity due to the difluoroacetic acid (estimated limits of detection in biological matrices 1–500 ng/mL) significantly varied for proteins with lower and higher charge state distributions. Matrix effects, as well as the specificity of the method were assessed for variable biological samples and pretreatment methods. This work demonstrates method development to improve the ability to target intact proteins directly by more affordable triple quadrupole mass spectrometry instrumentation, which could be beneficial in many application fields. [ABSTRACT FROM AUTHOR]

The "State-of-the-Art in Capillary Liquid Chromatography" panel discussion at the 43rd International Symposium on Capillary Chromatography (ISCC 2019) in Fort Worth, Texas, USA, was a thoughtful dialogue on current challenges and potential future directions in the field. The session included a general overview of the current state of the field, key drawbacks preventing widespread use of capillary liquid chromatography (LC) columns, and how these challenges might be overcome. In this article, we highlight some of the common themes that were discussed as part of this panel. [ABSTRACT FROM AUTHOR]

The electronic absorption spectra of alkanes are known to be broad and lack discrete band structures. Previous studies have suggested their HOMO-LUMO energy gaps could be used to understand the absorbance edges of these spectra. With the advent of a new benchtop vacuum ultraviolet (VUV) spectroscopic absorption detector, it is now possible to collect VUV absorption spectra (from 120 to 240 nm) for an extended range of structures under an inert gas phase environment more conveniently. The previously reported hypothesis was revisited and its limits were explored using a combination of new extended experimental VUV spectral data and theoretical quantum mechanics calculations. It was pointed out from this study that the first strong excitations of alkanes are not always the HOMO-LUMO transition. As a result, the HOMO-LUMO energy gap of alkanes should not be used directly as a universal and reliable parameter to understand their experimental absorbance edges. VUV spectral data for a larger variety of alkanes structures were reported and the relation between these structures and spectra was discussed. [ABSTRACT FROM AUTHOR]

Rationale: Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) provides detailed information for the analysis of ethoxylated alcohols and polymers. In this study, five friction reducers used in commercial hydraulic fracturing processes were analyzed in their as‐received form to identify their ethoxylated alcohol content. The friction reducers were then subjected to lab‐simulated downhole conditions. Characterization of friction reducers before and after being subjected to reactive conditions can provide fingerprints associated with produced oilfield waste for source apportionment and information on the stability of these key hydraulic fracturing additives. Methods: Five different industrially used friction reducers were analyzed for their ethoxylated alcohol content using MALDI‐TOF‐MS. Three different matrices were assessed for optimal response: α‐cyano‐4‐hydroxycinnamic acid, 2,5‐dihydroxybenzoic acid, and 2,5‐dihydroxybenzoic acid with 2,2,2‐trifluoroethanol (2,5‐DHB + E). Reaction times, temperatures, and sample matrices (deionized water, produced water inorganic, produced water, and produced water + shale core) were varied to assess changes in molecular weight distribution and polydispersity of the ethoxylated alcohols relative to their as‐received content. Results: A preference for the 2,5‐DHB + E matrix was observed. The friction reducers were found to contain ethoxylated alcohols with carbon chain lengths of 12 and 14 with degrees of ethoxylation ranging from 6 to 18. Upon being subjected to 100°C for 24 hours, the ethoxylated alcohols tended to polymerize further, returning higher average molecular weights. Less polymerization was seen in more complex matrices, as supported by dispersity calculations. Conclusions: Ethoxylated alcohol content was effectively determined in friction reducers using MALDI‐TOF‐MS. Although this is not a new technique to characterize ethoxylated alcohols, it has proven to be a quick and effective way to determine ethoxylated alcohol content in friction reducers in complex oilfield matrices. This technique can be used as a rapid and straightforward way to determine ethoxylated alcohol content in friction reducers and hydraulic fracturing wastewater for fingerprinting. [ABSTRACT FROM AUTHOR]

Rationale: Different supercharging agents were tested to study their effect on the intensity and charge state distributions of high‐molecular‐weight intact proteins. The goal of this work was to increase chargeability and ionization efficiency for proteins ranging from 66 to 150 kDa, to enable subsequent optimization of multiple reaction monitoring (MRM) mode transitions with a triple quadrupole mass spectrometer for potential top‐down quantitative analysis. Methods: Supercharging agents, such as meta‐nitrobenzyl alcohol (m‐NBA), dimethylsulfoxide, trifluoroethanol (TFE), and sulfolane were tested in different concentrations in 50/50 acetonitrile/water with 0.5% formic acid to examine the electrospray ionization response for three model proteins: bovine serum albumin (66 kDa), holo‐transferrin (78 kDa), and immunoglobulin G (150 kDa). The settings of ionization source temperature and mobile phase flow rate were also examined. MRM transitions were developed for a wide range of precursor ions for each protein, and limits of detection were determined for the proteins in the presence of favorable additive combinations. Results: For most of the proteins, m‐NBA (1%) and TFE (5%) worked most effectively, both to shift the charge state and increase intensity. This is the first report of the use of TFE as an effective agent for both increasing protein chargeability and ionization response. TFE increased ionization efficiency between 3‐ and 14‐fold for the model proteins studied. Increases in both source temperature and flow rate reduced the magnitude of the average charge state observed. The MRM transitions of six to eight different precursor ions of the proteins were optimized and limits of detection in the nanogram quantity on column were determined. Conclusions: The feasibility for top‐down quantitative analysis of high‐molecular‐weight proteins with a triple quadrupole mass spectrometer was demonstrated. Further, additives such as TFE can be highly beneficial for increased chargeability and response of the proteins. [ABSTRACT FROM AUTHOR]

In order to survive environmental changes, bacteria have stress responses, which protect them from adverse and variable conditions. Contamination can be a source of stress and bacterial responses can serve as an indicator of environmental abnormality. In this work, the biochemical effects of toxic compounds that stem from hydraulic fracturing were measured on the whole cell-derived fatty acid and protein compositions of Escherichia coli, Klebsiella oxytoca, Pseudomonas aeruginosa, Pseudomonas putida, Pseudomonas stutzeri, Aeromonas hydrophila, Bacillus cereus, and Bacillus subtilis. These microorganisms were exposed to elevated levels of benzene, ethanol, propanol, toluene, and salt. These were chosen to represent significant subsurface contamination or a surface spill. The fatty acid and protein profiles for the bacteria were analyzed using gas chromatography – vacuum ultraviolet spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry, respectively. Overall, different fatty acid and protein profiles were observed when the microorganisms were grown in the presence of the toxic compounds. The cells exhibited an increase in the saturated/unsaturated ratio and displayed the presence of branched and cyclopropane fatty acids when in the presence of common fracture fluid constituents to decrease membrane permeability which was confirmed by the analysis of produced water. This approach provides a potentially useful tool for environmental diagnosis, since proteins and fatty acids can act as a harbinger of ecological health. [ABSTRACT FROM AUTHOR]

The ability of different methods to analyze formaldehyde and other leachates from proppants was investigated under lab-simulated downhole conditions. These methods include high performance liquid chromatography (HPLC), headspace gas chromatography-vacuum ultraviolet spectroscopy (HS-GC-VUV), and headspace gas chromatography-mass spectrometry (HS-GC-MS). Two different types of resin-coated proppants, phenol-formaldehyde- and polyurethane-based, were examined. Each proppant was tested at different time intervals (1, 4, 15, 20, or 25 hours) to determine the timeframe for chemical dissolution. Analyses were performed at room temperature and heated (93 °C) to examine how temperature affected the concentration of leachates. Multiple matrices were examined to mimic conditions in subsurface environment including deionized water, a solution surrogate to mimic the ionic concentration of produced water, and recovered produced water. The complexity of these samples was further enhanced to simulate downhole conditions by the addition of shale core. The influence of matrix components on the analysis of formaldehyde was greatly correlated to the quantity of formaldehyde measured. Of the three techniques surveyed, HS-GC-MS was found to be better suited for the analysis of formaldehyde leachates in complex samples. It was found that phenol-formaldehyde resin coated proppants leached higher concentrations of formaldehyde than the polyurethane resin coated proppants. [ABSTRACT FROM AUTHOR]

This work focused on the development and validation of the analytical procedure using gas chromatography equipped with vacuum‐ultraviolet detection for the specific and sensitive determination of nine photoinitiators in food packages. Subsequently, a comparison of the combination of vacuum ultraviolet spectroscopy with gas chromatography and a developed gas chromatography with mass spectrometry method was performed. The vacuum‐ultraviolet spectra of all tested photoinitiators were collected and found to be highly distinct, even for isomers. Under the optimal conditions, the limits of detection for nine photoinitiators ranged from 1 to 5 mg/L using vacuum ultraviolet detection and from 0.15 to 0.5 mg/L using mass spectrometric detection. Both techniques were successfully applied for screening of photoinitiators in seven kinds of food packages and the obtained data showed good agreement (the relative difference was between 3 and 18%). The variability in concentrations found in triplicate samples was assessed to be below 18%. Predominantly benzophenone was found in all analysed samples in the range of 0.31–4.23 mg/kg. It appears to be preferably selected by food packaging manufacturers. This study proposes a new simple and sensitive technique used for analysis of photoinitiators that could be a good alternative to gas chromatography with mass spectrometry. [ABSTRACT FROM AUTHOR]

Copper(i) complexes supported by fluorinated 1,3,5-triazapentadienyl ligands have been used as catalysts for the oxidation of anthracene, naphthalene, and pyrene to the corresponding quinones, using H2O2 as an oxidant under mild conditions without an acid co-catalyst. Gas chromatography-vacuum ultraviolet spectroscopy (GC-VUV) combined with time-dependent density functional theory theoretical computations of absorption spectra was demonstrated as a new and useful tool-set for unknown determination in complex reaction mixtures, especially when standards are not available for spectral comparisons and product mixtures involve closely related isomers. The anthracene has been converted to 9,10-anthraquinone in quantitative yield using this copper catalyzed process. The oxidation of naphthalene afforded 1,4-naphthoquinone as the major product, and 1-naphthol and 2-naphthol as minor products. The pyrene oxidation resulted in 4,5-, 1,6-, and 1,8-pyrenequinones, among other products. The X-ray crystal structure of [N{(CF3)C(C6F5)N}2]CuNCCH3 is also reported. [ABSTRACT FROM AUTHOR]

Quantification of complex carbon‐containing mixtures is typically a very time‐intensive task with regards to the calibration process. A gas chromatograph with a flame ionization detector yields strong responses to organic compounds and provides a wide linear range over many orders of magnitude; however, responses for highly functionalized and heteroatom‐containing compounds can be variable. Here, a commercial Polyarc microreactor unit, placed before the flame ionization detector, was investigated as a means of normalizing carbon response across all compounds. The device includes two catalytic reaction chambers, ultimately converting all carbon atoms to methane evenly for flame ionization detection. Three groups of different complex mixtures from n‐alkane to terpene and polymer mixtures were analyzed to evaluate the potential for calibration‐free quantitation of the new detector arrangement. We have obtained accurate quantification results without time‐consuming calibration processes. The quantification of a terpene mixture and a polymer mixture confirms the ability of the detector for analyzing samples that either have complex physical or structural properties or wide concentration range. In summary, compared to other detectors, this methanizer – flame ionization detection system provides a simplified workflow, which can eliminate calibration steps and increase throughput. [ABSTRACT FROM AUTHOR]

Rationale: The importance of saccharides, the most abundant biomolecules on Earth, extends beyond their biological roles and to consumer products and industrial processes. Electrospray ionization tandem mass spectrometry (ESI‐MS/MS) is an attractive tool for the analysis of underivatized saccharides (US), but they tend to have relatively low sensitivities due to their low surface activities and lack of easily protonable or deprotonable chemical groups. An understanding of the influences that solvent parameters have on their signal intensities would enhance the usefulness of ESI‐MS/MS for their analysis. Methods: Solutions of glucose, a model analyte for US, in various combinations of solvent, additive, additive concentration, and pH were analyzed by flow injection analysis ESI‐MS/MS in both the positive and negative ionization mode. The blank‐corrected signal intensities of the solvent parameter combinations were then compared. Results: The addition of acetonitrile led to severe ionization suppression in the positive ionization mode through its competition with glucose for cation adduction. High signal intensity was achieved under wide pH and concentration ranges for methanol: water solutions containing ammonium trifluoroacetate in the positive ionization mode. The highest signal intensities for acetonitrile: water solutions were those containing ammonium formate or lithium fluoride in the negative ionization mode. Conclusions: An understanding of the influence of solvent parameters on the signal intensity of a given analyte is useful for guiding the selection process of mobile phases/flow solvents that lead to low limits of detection or the minimization of matrix effects by allowing its detection at high dilution factors. [ABSTRACT FROM AUTHOR]

Abstract: A multipath liquid chromatography with mass spectrometry instrument was constructed with the help of restricted access media to online segregate small and large molecules. This liquid chromatography system was custom built with five pumps and three two‐position six‐port valves to control the flow in a multipath system for the simultaneous analysis of small molecules and proteins. On separate chromatographic channels, small molecules trapped and proteins excluded from the online restricted access media were analyzed downstream using high‐efficiency columns and a triple quadrupole mass spectrometer. A model sample, which included five proteins and 22 small molecules with different physicochemical properties, was used to evaluate the system. Following injection, the complete multipath separation and detection was performed in 22 min. Protein exclusion by the restricted access media was not quantitative. Four commercial trap columns were evaluated for their exclusion efficiency toward the proteins. Exclusion efficiency varied from <50% to only a maximum of 75% exclusion across the trap columns tested. An attempt was made to optimize the exclusion efficiency using different flow rates, flow rate gradients, and different additives both in the sample and the mobile phases. Protein exclusion was still erratic and generally nonquantitative. [ABSTRACT FROM AUTHOR]

Abstract: Cannabinoids are the primary bioactive constituents of Cannabis sativa and Cannabis indica plants. In this work, gas chromatography in conjunction with triple quadrupole mass spectrometry in multiple reaction monitoring mode was explored for determination of cannabinoids from a surrogate hops matrix. Gas chromatography with mass spectrometry is a reasonable choice for the analysis of these compounds; however, such methods are susceptible to false positives for Δ9‐tetrahydrocannabinol, due to decarboxylation of Δ9‐tetrahydrocannabinolic acid, its acid precursor, in the hot injection port. To avoid this transformation, the carboxyl group of Δ9‐tetrahydrocannabinolic acid was protected through a silylation reaction. Multiple reaction monitoring transitions for both unmodified and silylated cannabinoids were developed and the fragmentation pathways for the different species were assigned. Precision and accuracy were evaluated for cannabinoids spiked into hops at different levels. The developed methods provided good linearity (R2 > 0.99) for all the cannabinoids with a linear range from 0.15 to 20 mg/L, and with limits of detection in the orders of low‐ to mid‐picogram on column. The recoveries for the cannabinoids were generally between 75 and 120%. Precisions (<6% coefficient of variation) were within acceptable ranges. [ABSTRACT FROM AUTHOR]

Abstract: Cannabis has garnered a great deal of new attention in the past couple of years in the United States due to the increasing instances of its legalization for recreational use and indications for medicinal benefit. Despite a growing number of laboratories focused on cannabis analysis, the separation science literature pertaining to the determination of cannabis natural products is still in its infancy despite the plant having been utilized by humans for nearly 30 000 years and it being now the most widely used drug worldwide. This is largely attributable to the restrictions associated with cannabis as it is characterized as a schedule 1 drug in the United States. Presented here are reviewed analytical methods for the determination of cannabinoids (primarily) and terpenes (secondarily), the primary natural products of interest in cannabis plants. Focus is placed foremost on analyses from plant extracts and the various instrumentation and techniques that are used, but some coverage is also given to analysis of cannabinoid metabolites found in biological fluids. The goal of this work is to provide a collection of relevant separation science information, upon which the field of cannabis analysis can continue to grow. [ABSTRACT FROM AUTHOR]

Vanilla extracts are widely used as flavoring ingredients in foods, beverages, perfumes, and pharmaceuticals. Due to the high cost of producing high-quality natural extracts, artificial flavorings, such as ethyl vanillin and coumarin, are often used. For food safety and to ensure high-quality products, it is important to differentiate between natural and artificial extracts. In this work, gas chromatography-vacuum ultraviolet spectroscopy (GC-VUV) was used for the determination of natural and artificial flavoring compounds in vanilla extract samples. Since the GC-VUV software is able to deconvolve co-eluting peaks based on their unique VUV/UV absorption spectra (125-240 nm), a compromise between resolution and speed of analysis (6- and 14-min runs on different polarity columns) could be made. LODs between 0.42 and 2.0 μg mL were obtained for the tested flavoring compounds. Vanillin was present in extracts at the highest concentrations, from 108 to 5817 μg mL. [ABSTRACT FROM AUTHOR]

Groundwater quality and quantity is of extreme importance as it is a source of drinking water in the United States. One major concern has emerged due to the possible contamination of groundwater from unconventional oil and natural gas extraction activities. Recent studies have been performed to understand if these activities are causing groundwater contamination, particularly with respect to exogenous hydrocarbons and volatile organic compounds. The impact of contaminants on microbial ecology is an area to be explored as alternatives for water treatment are necessary. In this work, we identified cultivable organic-degrading bacteria in groundwater in close proximity to unconventional natural gas extraction. Pseudomonas stutzeri and Acinetobacter haemolyticus were identified using matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF MS), which proved to be a simple, fast, and reliable method. Additionally, the potential use of the identified bacteria in water and/or wastewater bioremediation was studied by determining the ability of these microorganisms to degrade toluene and chloroform. In fact, these bacteria can be potentially applied for in situ bioremediation of contaminated water and wastewater treatment, as they were able to degrade both compounds. [ABSTRACT FROM AUTHOR]

The separation and identification of natural mixtures of terpenes is challenging and laborious. A gas chromatographic method based on vacuum ultraviolet spectroscopic detection, which is characterized by full-scan absorption in the range of 125-240 nm, was developed and applied to analyze terpenes. In this study, the vacuum ultraviolet absorption spectra of 41 different standard terpenes were investigated and compared. The spectra were found to be highly featured and easily differentiated. Several commercial turpentine samples were analyzed and the vacuum ultraviolet detector demonstrated good specificity for qualitative identification of constituent terpenes. A total of 31 terpenes were detected in the four turpentine samples. α-Pinene was the predominant terpene ranging from 744.2 ± 9.7 to 917 ± 21 mg/mL. The other major constituents in the turpentines included β-pinene, δ-3-carene, camphene, and p-isopropyltoluene. Deconvolution of co-eluting signals of terpenes was achieved utilizing the data analysis software. The technique has been demonstrated to be a powerful tool for reliable and accurate qualitative and quantitative analysis of terpenes from complex natural mixtures. [ABSTRACT FROM AUTHOR]

The vacuum ultraviolet spectrophotometer was developed recently as an alternative to existing gas chromatography detectors. This detector measures the absorption of gas-phase chemical species in the range of 120-240 nm, where all chemical compounds present unique absorption spectra. Therefore, qualitative analysis can be performed and quantification follows standard Beer-Lambert law principles. Different fields of application, such as petrochemical, food, and environmental analysis have been explored. Commonly demonstrated is the capability for facile deconvolution of co-eluting analytes. The concept of additive absorption for co-eluting analytes has also been advanced for classification and speciation of complex mixtures using a data treatment procedure termed time interval deconvolution. Furthermore, pseudo-absolute quantitation can be performed for system diagnosis, as well as potentially calibrationless quantitation. In this manuscript an overview of these features, the vacuum ultraviolet spectrophotometer instrumentation, and performance capabilities are given. A discussion of the applications of the vacuum ultraviolet detector is provided by describing and discussing the papers published thus far since 2014. [ABSTRACT FROM AUTHOR]

Restricted access media are generally composed from multi-modal particles that combine a size excluding outer surface and an inner-pore retention mechanism for small molecules. Such materials can be used for either online isolation and pre-concentration of target small molecules or removal of small molecule interferences from large macromolecules, such as proteins in complex biological matrices. Thus, they are considered as enhanced online solid-phase extraction materials. We evaluated the efficiency and trapping capacity of different semi-permeable surface restricted access media columns (C18, C8, and C4 inner pores) for four model small molecule compounds (dopamine hydrochloride, acetaminophen, 4-hydroxybenzoic acid, and diethyl phthalate) having variable physicochemical properties. We further studied the effect of mobile phase flow rate (0.25, 0.5, 1, and 2 mL/min) and pH, using 98:2 0.5% acetic acid in water/ methanol (pH 2.88) and 5 mM ammonium acetate in 98:2 water/methanol (pH 6.61) as mobile phases. Breakthrough curves generated using frontal analysis were analyzed to determine important chromatographic parameters specific for each of the studied compounds. Experimental determination of these parameters allowed selection of the most efficient trap column and the best loading mobile phase conditions for maximal solute enrichment and pre-concentration on restricted access media trap columns. [ABSTRACT FROM AUTHOR]

The separation of intact proteins is inherently more complex than that of small molecules using reversed-phase liquid chromatography. The goal of this work was to determine a reasonable set of operational parameters (a recommended starting point for other analysts) for the separation of intact proteins and their detection by triple quadrupole mass spectrometry. Although protein separations have been studied for many years, the direct detection of intact proteins with mass spectrometry requires special considerations of mobile phase additives to achieve efficient separation and sensitive detection. Myoglobin, cytochrome c, lactalbumin, lysozyme, and ubiquitin were used as model analytes to investigate chromatographic method development using a triple quadrupole mass spectrometer and detection by multiple reaction monitoring. Chromatographic parameters including the concentration of trifluoroacetic acid, flow rate, gradient slope, temperature, mobile phase composition, and stationary phase chemistry were evaluated. Protein charge state profiles were also monitored for temperature and modifier effects. An optimized method using 0.2 mL/min flow rate, 15% gradient slope, and 75°C with a combined trifluoroacetic acid and formic acid modified mobile phase was developed. [ABSTRACT FROM AUTHOR]

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) is an emerging technique for microbial identification, characterization, and typing. The single colony method can be used for obtaining a protein fingerprint or profile unique to each microorganism. This technique has been mainly used in the clinical field, but it also has significant potential in the environmental field. The applications of MALDI-TOF MS in environmental microbiology are discussed in this review. An overview on the use of MALDI-TOF MS for environmental proteomics and metabolomics is given as well as its use for bacterial strain typing and bioremediation research. A more detailed review on the use of this technique for the identification, differentiation, and categorization of environmental microorganisms is given. Some of the parameters that can influence the results and reproducibility of MALDI-TOF MS are also discussed. [ABSTRACT FROM AUTHOR]

There are various reversed-phase stationary phases that offer significant differences in selectivity and retention. To investigate different reversed-phase stationary phases (aqueous stable C18, biphenyl, pentafluorophenyl propyl, and polar-embedded alkyl) in an automated fashion, commercial software and associated hardware for mobile phase and column selection were used in conjunction with liquid chromatography and a triple quadrupole mass spectrometer detector. A model analyte mixture was prepared using a combination of standards from varying classes of analytes (including drugs, drugs of abuse, amino acids, nicotine, and nicotine-like compounds). Chromatographic results revealed diverse variations in selectivity and peak shape. Differences in the elution order of analytes on the polar-embedded alkyl phase for several analytes showed distinct selectivity differences compared to the aqueous C18 phase. The electron-rich pentafluorophenyl propyl phase showed unique selectivity toward protonated amines. The biphenyl phase provided further changes in selectivity relative to C18 with a methanolic phase, but it behaved very similarly to a C18 when an acetonitrile-based mobile phase was evaluated. This study shows the value of rapid column screening as an alternative to excessive mobile phase variation to obtain suitable chromatographic settings for analyte separation. [ABSTRACT FROM AUTHOR]

Currently, there are limited effective means of drug disposal for consumers, and this creates a gateway to illicit use and environmental contamination. Here, we evaluated the efficacy of a new drug disposal product, composed from a slurry of activated carbon, which claims to sequester up to 100% of a drug's active ingredient when the loading capacity is not exceeded, making it safe to dispose in landfill. High-performance liquid chromatography with tandem mass spectrometry was applied to quantify as many as 24 drugs (opiates, barbiturates, statins, amphetamine, and benzodiazepine drugs) in the residual solvent solution from the product. Calibration curves were established in the concentration ranges of 0.25-7.0 μg/mL and showed good linearity. The limits of detection varied from 0.001 to 0.02 μg/mL, depending on the drug. Accuracy ranged from 80 to 111% for quality control samples, with a few minor exceptions. Precision overall varied between 0.2 to 12.7%. In sample bottles tested, where active ingredient of the loaded drug was below the maximum sorption capacity stated on the label, 98 to >99.9% of the active ingredient was sequestered. Percent active ingredient adsorbed was slightly lower in bottles loaded in excess of label specifications. [ABSTRACT FROM AUTHOR]

Accurate and specific analysis of target molecules in complex biological matrices remains a significant challenge, especially when ultra-trace detection limits are required. Liquid chromatography with mass spectrometry is often the method of choice for bioanalysis. Conventional sample preparation and clean-up methods prior to the analysis of biological fluids such as liquid-liquid extraction, solid-phase extraction, or protein precipitation are time-consuming, tedious, and can negatively affect target recovery and detection sensitivity. An alternative or complementary strategy is the use of an off-line or on-line in situ derivatization technique. In situ derivatization can be incorporated to directly derivatize target analytes in their native biological matrices, without any prior sample clean-up methods, to substitute or even enhance the extraction and preconcentration efficiency of these traditional sample preparation methods. Designed appropriately, it can reduce the number of sample preparation steps necessary prior to analysis. Moreover, in situ derivatization can be used to enhance the performance of the developed liquid chromatography with mass spectrometry-based bioanalysis methods regarding stability, chromatographic separation, selectivity, and ionization efficiency. This review presents an overview of the commonly used in situ derivatization techniques coupled to liquid chromatography with mass spectrometry-based bioanalysis to guide and to stimulate future research. [ABSTRACT FROM AUTHOR]

The determination of nicotine and its major metabolites (cotinine and anabasine) in fish tissue was performed using liquid chromatography and tandem mass spectrometry. Marine and freshwater fish were purchased from local grocery stores and were prepared based on a quick, easy, cheap, effective, rugged, and safe sample preparation protocol. To determine the highly polar compounds, hydrophilic interaction liquid chromatography was also used. There were modest suppressions on measured nicotine signals (10%) due to the matrix effects from marine fish but no obvious effects on freshwater fish signals. Method validation was incorporated with internal standards and carried out with matrix-matched calibration. The detection limits for nicotine, cotinine, and anabasine were 9.4, 3.0, and 1.5 ng/g in fish, respectively. Precision was quite acceptable returning less than 8% RSD at low, medium, and high concentrations. Acceptable and reproducible extraction recoveries (70-120%) of all three compounds were achieved, except for anabasine at low concentration (61%). The method was then applied to define nicotine bioaccumulation in a fathead minnow model, which resulted in rapid uptake with steady state internal tissue levels, reached within 12 h. This developed method offers a fast, easy, and sensitive way to evaluate nicotine and its metabolite residues in fish tissues. [ABSTRACT FROM AUTHOR]

Here we present data using a bioluminescent dinoflagellate, Pyrocystis lunula, in a toxicological bioassay to rapidly assess potential instances of groundwater contamination associated with natural gas extraction. P. lunula bioluminescence can be quantified using spectrophotometry as a measurement of organismal viability, with normal bioluminescent output declining with increasing concentration(s) of aqueous toxicants. Glutaraldehyde and hydrochloric acid (HCl), components used in hydraulic fracturing and shale acidization, triggered significant toxicological responses in as little as 4 h. Conversely, P. lunula was not affected by the presence of arsenic, selenium, barium, and strontium, naturally occurring heavy metal ions potentially associated with unconventional drilling activities. If exogenous compounds, such as glutaraldehyde and HCl, are thought to have been introduced into groundwater, quantification of P. lunula bioluminescence after exposure to water samples can serve as a cost-effective detection and risk assessment tool to rapidly assess the impact of putative contamination events attributed to unconventional drilling activity. [ABSTRACT FROM AUTHOR]

In the search for stable and efficient photocatalysts beyond TiO2, the tungsten-based oxide semiconductors silver tungstate (Ag2WO4), copper tungstate (CuWO4), and zinc tungstate (ZnWO4) were prepared using solution combustion synthesis (SCS). The tungsten precursor's influence on the product was of particular relevance to this study, and the most significant effects are highlighted. Each sample's photocatalytic activity towards methyl orange degradation was studied and benchmarked against their respective commercial oxide sample obtained by solid-state ceramic synthesis. Based on the results herein, we conclude that SCS is a time- and energy-efficient method to synthesize crystalline binary tungstate nanomaterials even without additional excessive heat treatment. As many of these photocatalysts possess excellent photocatalytic activity, the discussed synthetic strategy may open sustainable materials chemistry avenues to solar energy conversion and environmental remediation. [ABSTRACT FROM AUTHOR]

Trillions of liters of wastewater from oil and gas extraction are generated annually in the US. The contribution from unconventional drilling operations (UDO), such as hydraulic fracturing, to this volume will likely continue to increase in the foreseeable future. The chemical content of wastewater from UDO varies with region, operator, and elapsed time after production begins. Detailed chemical analyses may be used to determine its content, select appropriate treatment options, and identify its source in cases of environmental contamination. In this study, one wastewater sample each from direct effluent, a disposal well, and a waste pit, all in West Texas, were analyzed by gas chromatography-mass spectrometry, inductively coupled plasma-optical emission spectroscopy, high performance liquid chromatography-high resolution mass spectrometry, high performance ion chromatography, total organic carbon/total nitrogen analysis, and pH and conductivity analysis. Several compounds known to compose hydraulic fracturing fluid were detected among two of the wastewater samples including 2-butoxyethanol, alkyl amines, and cocamide diethanolamines, toluene, and o-xylene. Due both to its quantity and quality, proper management of wastewater from UDO will be essential. [ABSTRACT FROM AUTHOR]

Some might consider gas chromatography (GC) a mature technique. However, several substantial advances in GC technology in the past few years have proven that there is still room for innovation. Here, we present a brief history of GC detectors, leading to the most recent introduction of a vacuum ultraviolet (VUV) absorption detector, which has been shown to provide significant benefits in areas where mass spectrometry (MS) detection has problems. It provides full scan absorption spectra in the range of 120-240 nm, where all gas-phase chemical species absorb and have unique spectral features. VUV detection can be used to deconvolute signals from coeluted analytes and has detection sensitivity on par with MS detection. [ABSTRACT FROM AUTHOR]