Gas Chromatography Of Samples Research Articles

The analysis of e-liquids: A study on chemical diversity and metal content using gas chromatography-mass spectrometry and inductively coupled plasma-mass spectrometry.

This work aimed to determine the chemical composition of 22 e-liquids available on the Slovenian market. Four different gas chromatography (GC) sample introduction techniques; headspace-GC-mass spectrometry (HS-GC-MS), liquid injection-GC-MS (LI-GC-MS), HS-solid-phase microextraction-GC-MS (HS-SPME-GC-MS), and direct-immersion-SPME-GC-MS (DI-SPME-GC-MS) were employed for qualitative analysis. Various experimental parameters were assessed for each GC sample introduction technique to maximize compound identification. Despite e-liquid packaging reporting a maximum of eight compounds, GC-MS identified more compounds in most samples, especially in menthol-flavored (58 identifiable compounds by HS-SPME-GC-MS), followed by nicotine-containing and fruit-flavored samples. HS-SPME-GC-MS identified the highest number of compounds, followed by HS-GC-MS, DI-SPME-GC-MS, and LI-GC-MS. Nicotine quantification in six samples was performed by LI-GC-MS with dilution in methanol. Nicotine concentration in samples ranged from 16.5±0.5 to 18.5±0.4 mg/mL, which was below the declared concentration of 20mg/mL. Additionally, quantitative analysis of metals in e-liquids was performed by inductively coupled plasma-MS after microwave-assisted wet acid digestion. Iron was the most abundant metal, with its content ranging from 0.024 to 0.354µg/g. Barium, bismuth, copper, and tin were also determined in several e-liquids.

An in situ gas chromatograph with automatic detector switching between PTR- and EI-TOF-MS: isomer-resolved measurements of indoor air

Abstract. We have developed a field-deployable gas chromatograph (GC) with thermal desorption preconcentration (TDPC), which is demonstrated here with automatic detector switching between two high-resolution time-of-flight mass spectrometers (TOF-MSs) for in situ measurements of volatile organic compounds (VOCs). This system provides many analytical advances, including acquisition of fast time–response data in tandem with molecular speciation and two types of mass spectral information for each resolved GC peak: molecular ion identification from Vocus proton transfer reaction (PTR) TOF-MS and fragmentation pattern from electron ionization (EI) TOF-MS detection. This system was deployed during the 2018 ATHLETIC campaign at the University of Colorado Dal Ward Athletic Center in Boulder, Colorado, where it was used to characterize VOC emissions in the indoor environment. The addition of the TDPC-GC increased the Vocus sensitivity by a factor of 50 due to preconcentration over a 6 min GC sample time versus direct air sampling with the Vocus, which was operated with a time resolution of 1 Hz. The GC-TOF methods demonstrated average limits of detection of 1.6 ppt across a range of monoterpenes and aromatics. Here, we describe the method to use the two-detector system to conclusively identify a range of VOCs including hydrocarbons, oxygenates, and halocarbons, along with detailed results including the quantification of anthropogenic monoterpenes, where limonene accounted for 47 %–80 % of the indoor monoterpene composition. We also report the detection of dimethylsilanediol (DMSD), an organosiloxane degradation product, which was observed with dynamic temporal behavior distinct from volatile organosiloxanes (e.g., decamethylcyclopentasiloxane, D5 siloxane). Our results suggest DMSD is produced from humidity-dependent heterogeneous reactions occurring on surfaces in the indoor environment, rather than formed through gas-phase oxidation of volatile siloxanes.

Determination of Volatile Organic Compounds in Recycled Polyethylene Terephthalate Fibers by HS-GC-FID to Evaluate the Efficiency of Testing Conditions

A method to determine the volatile organic compounds (VOCs) in the recycled polyethylene terephthalate fiber was presented by using the headspace sampling-gas chromatography coupled to flame ionization detector (HS-GC-FID), in order to evaluate the level of VOC contamination. The extraction variables, such as the incubation temperature, the pre-incubation time and the size of the vial, were also studied. The effects on the determination of VOC were also compared using two type chromatographic columns. The optimal conditions were found using a headspace sampling for 20 min at 100 °C, where 120 mL vials and TM-1 column were prior to analysis of benzene compounds in PET(polyethylene terephthalate) fibers. The results can be used in analysis of VOC from recycled PET fibers.

Development of a lithium ion cell enabling in situ analyses of the electrolyte using gas chromatographic techniques

Monitoring the electrolyte decomposition in lithium ion battery electrolytes is key to understand their influence on electrochemical cell performance. Gas chromatographic techniques have been reported to provide valuable information benefiting from the separation of the analytes of interest. During this study a new cell design has been developed, which provides the opportunity to carry out in situ analyses. For this purpose, the cell based on the 18650 format was designed to be compatible with gas chromatographic sampling routines e.g. by solid phase microextraction. In this case study we were able to provide information about the consumption of vinylene carbonate over a course of 200 cycles, while retaining a good cycling performance. Additionally, the formation and accumulation of one of the major decomposition products of the electrolyte was monitored. The developed new technique will contribute to gain information about the electrolyte constituents beyond state-of-the-art post mortem techniques.

Bioethanol production from agarophyte red seaweed, Gelidium elegans, using a novel sample preparation method for analysing bioethanol content by gas chromatography.

In this study, Gelidium elegans is investigated for ethanol production. A combination of factors including different temperatures, acid concentration and incubation time was evaluated to determine the suitable saccharification conditions. The combination of 2.5% (w/v) H2SO4 at 120°C for 40min was selected for hydrolysis of the seaweed biomass, followed by purification, and fermentation to yield ethanol. The galactose and glucose were dominant reducing sugars in the G. elegans hydrolysate and under optimum condition of dilute acid hydrolysis, 39.42% of reducing sugars was produced and fermentation resulted in ethanol concentration of 13.27 ± 0.47g/L. A modified method was evaluated for sample preparation for gas chromatography (GC) analysis of the ethanol content. A solvent mixture of acetonitrile and iso-butanol precipitated dissolved organic residues and reduced water content in GC samples at least by 90%. Results showed that this method could be successfully used for bioethanol production from seaweed.

CO2 Electroreduction to Hydrocarbons on Carbon-Supported Copper Nanoparticles

High-surface area catalysts are crucial for electrochemical devices that rely on kinetically-limited electrochemical reactions. Proton exchange membrane fuel cells (PEMFC) and electrolyzers are examples of such devices. Commercialization of these devices became possible due to the development of nanoscale Pt catalysts on high-surface area carbon supports.Here we discuss the electrocatalytic activities of carbon-supported Cu nanoparticles for CO2 electroreduction, a reaction that is also kinetically limited and have a potential for implemention in CO2 electrolyzers for the production of hydrocarbon fuels such as CH4 and C2H4. Cu nanoparticles supported on Carbon Black (VC), Ketjen Black (KB) and Single Wall Carbon Nanotubes (SWNT) are synthesized and their activities towards CO2 electroreduction to hydrocarbon fuels (CH4, C2H2, C2H4 and C2H6) are evaluated using online gas chromatography (GC). Faradaic efficiencies of three home-made catalysts towards CO2 electroreduction are compared to that of commercial 20 wt% Cu/VC and films of electrodeposited Cu.Supported Cu catalysts were synthesized using three different synthetic routes. X-Ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used for nanoparticle ex-situ analysis. The average Cu particle size as determined by Scherer’s equation was 12, 19, 24 and 27 nm for 40 wt% Cu/VC, 20 wt% Cu/SWNT, 50 wt% Cu/KB and commercial 20 wt% Cu/VC, respectively. Pb underpotential deposition was used for in-situ evaluation of the electrochemical surface area (ECSA) of Cu nanoparticles and Cu films [1]. Electrodeposited Cu films had a smooth surface, close to the mirror-polished surface of a RDE electrode.Activity of Cu nanoparticles towards CO2 electroreduction to hydrocarbon fuels was evaluated using a sealed RDE setup connected to GC. Thin films of 40 wt% Cu/VC, commercial 20 wt% Cu/VC, 20 wt% Cu/SWNT and 50 wt% Cu/KB were deposited on the surface of custom-made 7 mm glassy carbon disks (Pine Instruments, Inc), following a well-established protocol in the PEMFC community [2]. GC sampling from the electrochemical cell was performed at 5, 25, 45 and 65 min from the start of experiment, while holding the electrode potential at -1.2, -1.4, -1.6, -1.8, -2 and -2.2V vs. Ag/AgCl reference electrode. CH4 and C2H4 were the only gaseous hydrocarbons detected during CO2 electroreduction on Cu nanoparticles and Cu films. Figure 1 compares faradaic efficiencies vs. potential for CO, H2, CH4 and C2H4 generation on thin films of 40 wt% Cu/VC (12 nm Cu particle size) and electrodeposited Cu. In the potential region between -1.4 and -2.2V, the hydrocarbon product distribution is dominated by C2H4 for Cu nanoparticles (Fig. 1a) and CH4 for the films of electrodeposited Cu (Fig. 1b). In addition, the onset potential for C2H4 generation is shifted by 0.2 V (-1.4 vs. -1.6 V) for 40 wt% Cu/VC vs electrodeposited Cu, indicative of the higher activity of Cu nanoparticles towards C2H4 generation. Higher activity and reverse product distribution for 40 wt% Cu/VC vs electrodeposited Cu films is likely due to a large number of under-coordinated sites, such as corners, edges and defects on the surface of nanoparticles vs. a smooth Cu surface [3].This presentation will discuss the differences in electrocatalytic activities of four supported catalysts towards CO2 electroreduction and the influence of support on product distribution in more detail. Acknowledgements OAB is grateful to the Office of Naval Research for financial support of this project.

Near infrared reflectance spectroscopy (NIRS) for large scale screening of fatty acid profile in peanut (Arachis hypogaeaL.)

Breeding programmes dealing with the modifications of the fatty acid profile in oilseed crops require large number of chromatographic analysis. This study was conducted to characterize the potential of near infrared reflectance spectroscopy (NIRS) for the fatty acid analysis of intact single seeds of peanut. The material consisted of 1000 mutant entries of M4 with varying fatty acid profile determined by gas chromatography (GC). Spectra from intact single seeds of the mutant entries were collected with a specially designed adapter using standard monochromator instrument. Calibration equations were developed for the calibration set of 800 mutant entries and were further validated with cross-validation and external-validation set consisting each of 100 mutant entries. Among the three regression models, the spectra with modified partial least square regression model (mPLS) after second derivative pretreatment with SNV and detrend scatter correction had the best calibration and satisfactory prediction abilities. The r2 between NIRS and GC was 0.79 (palmitic acid), 0.91 (oleic acid) and 0.89 (linoleic acid) in cross validation, demonstrating the high reliability of NIRS in determining these fatty acid concentrations in intact single seeds. NIRS permitted analysis of about 40 samples per hour as against 1-2 samples in GC. Research clearly indicated that NIRS prediction of fatty acid profile using intact seeds was non-destructive, accurate, rapid and should be especially useful for early generation selection.

Analysis of volatile flavor compounds in top fermented wheat beer by headspace sampling-gas chromatography

Li Huimin, Li Hongjun*, Liu Xiuhua, Chen Bing (School of Agriculture and Food Engineering, Shandong University of Technology, Zibo 255049, China) Abstract: Headspace sampling-gas chromatography (HS-GC) coupled with an internal standard method (ISM) was developed to analyze the volatile flavor compounds in top fermented wheat beer in the laboratory. Eight compounds, i.e. acetaldehyde, N-propanol, ethyl acetate, isobutyl alcohol, isoamyl alcohol, isoamyl acetate, ethyl hexanoate and ethyl octanoate were separated and quantified. This method was validated to ensure the quality of the results: the precision was satisfactory with relative standard deviation (RSD) in the range of 1.51%-4.22%, recoveries for all the analytes ranged from 95.15% to 99.85%, and the limits of detection were in the range of 0.0002-0.024 mg/L. Results of real wheat beer samples analyzed using this method showed that the volatile compound concentrations were in the range of 0.08-99.91 mg/L. Results suggested that this method exhibited good reproducibility, selectivity and high precision, and it can be useful for the analysis of routine beer samples. Keywords: top fermentation, wheat beer, flavor detection, volatile flavor compounds, headspace sampling-gas chromatography, internal standard method DOI: 10.3965/j.ijabe.20120502.009 Citation: Li H M, Li H J, Liu X H, Chen B. Analysis of volatile flavor compounds in top fermented wheat beer by headspace sampling-gas chromatography. Int J Agric & Biol Eng, 2012; 5(2): 67

A shock tube and chemical kinetic modeling study of the pyrolysis and oxidation of butanols

The pyrolysis and oxidation of all four butanols (n-, sec-, iso- and tert-) have been studied at pressures from 1 to 4atm and temperatures of 1000–1800K behind reflected shock waves. Gas chromatographic sampling at different reaction times varying from 1.5 to 3.1ms was used to measure reactant, intermediate and product species profiles in a single-pulse shock tube. In addition, ignition delays were determined at an average reflected shock pressure of 3.5atm at temperatures from 1250 to 1800K. A detailed chemical kinetic model consisting of 1892 reactions involving 284 species was constructed and tested against species profiles and ignition delays. The little-known chemistry of enols is included in this work to explain the temperature dependence of acetaldehyde produced in the thermal decomposition of isobutanol.

Using an Electronic Nose to Rapidly Assess Grandlure Content in Boll Weevil Pheromone Lures

Samples of pheromone lures used in boll weevil, Anthonomus grandis (Boheman), eradication programs are routinely analyzed by Gas Chromatography (GC) to ensure lures are adequately dosed with grandlure, the synthetic aggregation pheromone produced by male weevils. However, preparation of GC samples is tedious, time consuming, and requires a moderate level of experience. We examined the use of a commercially-available electronic nose (e-nose) for rapidly assessing the grandlure contents of lures. The e-nose was trained to recognize headspace collections of grandlure emitted from new lures and after lures were aged under field conditions for 4 d, 7 d, 10 d, and 14 d. Based on cross-validation of the training set, the e-nose was 82% accurate in discriminating among the different age classes of lures. Upon sampling headspace collections of pheromone from a different set of field-aged lures, the e-nose was <50% accurate in discriminating 4 d, 7 d, and 10 d aged lures from the other age classes of lures. However, the e-nose identified new and 14 d aged lure samples with 100% accuracy. In light of these findings, e-nose technology shows considerable promise as an alternative approach for rapidly assessing the initial grandlure contents of lures used in boll weevil eradication programs.

The improvement of blowout limit in partially/fully premixed flames with geometrically modified bluffbody bases

The improvement of the lean blowout limit of bluffbody stabilized methane flames is investigated. The flame configuration consists of a hybrid of partially and fully premixed flames, which is produced by injecting methane jets from a streamline-shaped bluffbody into a fully premixed methane/air crossflow. Additional geometric modifications from the original bluffbody base are such that the base has two-dimensionally modified geometries and three-dimensional local cavities. We observe that the blowout limit of the hybrid configuration is extended by up to ~12% (in terms of the equivalence ratio of the crossflow) with the modified geometries. Gas chromatographic sampling and particle image velocimetry (PIV) show that high fuel mole fraction regions coexist with regions of low speed flow for the modified geometries. Further PIV analysis shows that the downstream flow fields of the modified bases generally have a larger number of incoherent vortices and lower strain rate in comparison with those of the unmodified base.

Injection port derivatization following sonication-assisted ion-pair liquid–liquid extraction of nonsteroidal anti-inflammatory drugs

In this paper, a sonication-assisted ion-pair liquid–liquid extraction approach, combined with injection port derivatization and gas chromatographic (GC) analysis, was developed to extract and detect nonsteroidal anti-inflammatory drugs (NSAIDs). In this procedure, the target analytes in the sample solution were converted into their ion-pair complexes (carboxylate ion-pairs) with tetrabutylammonium hydrogen sulfate. The ion-pairs were then extracted by an organic solvent (ethyl acetate) with the assistance of sonication. The factors influential to extraction, including type of organic solvent, concentration of ion-pair reagent, pH values of sample solution, sonication time duration and salt addition, were investigated in detail. After extraction, the organic phase containing ion-pair complexes was injected to GC sample port. Upon injection, the carboxylate ion-pairs were derivatized promptly under high temperature to yield butyl esters, which were more suitable for GC analysis. The conditions for injection port derivatization, such as injection port temperature and purge off time, were also examined. This newly established approach afforded the limits of detection between 0.44 and 2.75 ng L −1 for the tested NSAIDs, with relative standard deviations less than 5.4%.

Structural identification and mass spectral interpretation of C3n highly branched alkanes in sediment and aquatic extracts and evidence for their anthropogenic origin

The structures of two distinctive series of C3n highly branched alkanes (HBAs), previously detected in sedimentary and aquatic extracts, were identified as polypropylene (PP) oligomers with different end groups, using gas chromatography (GC) and mass spectrometry (MS) correlation with diastereoisomeric mixtures of authentic C15 and C18 standards. A C15 member of the earlier eluting series was assigned as 2,4,6,8-tetramethylundecane and a C15 member of the later eluting series as 4,6,8-trimethyldodecane. The C3n HBA GC–MS profiles of extracts from a typical PP GC sample vial lid were also shown to closely match those previously detected in sediment and water extracts, providing convincing evidence that the purported environmental occurrences are a result of PP contamination. Both C3n series correspond to the first eluting diastereoisomer of the respective standards, also consistent with an industrial isotactic PP source. Mass spectra of all five standards are presented to help assignment of new polymethyl alkanes.

A new high-pressure vapour–liquid equilibrium apparatus

A new variable volume static type high-pressure VLE apparatus has been designed, constructed, and tested on a number of systems. The apparatus has an operating temperature range from 250 K to 393 K and pressure range from absolute vacuum up to 120 bar. The stainless steel equilibrium cell has sapphire viewing windows and a novel liquid sampling technique utilizing gas chromatographic sampling valves which permit phase sampling without disturbance to the equilibrium condition. The apparatus was tested by measuring VLE isotherms for some binary systems, viz., carbon dioxide + toluene at 283.25 K, 311.15 K, 353.15 K and 391.45 K; carbon dioxide + methanol at 263.15 K, 273.15 K, 313.15 K, 363.15 K and 373.15 K; and propane + 1-propanol at 323.15 K, 378.15 K and 393.15 K. Satisfactory modeling was obtained of the measured VLE data and thermodynamic consistency tests showed the data to be not inconsistent.

Gas chromatography/flame ionisation detection mass spectrometry for the detection of endogenous urine metabolites for metabonomic studies and its use as a complementary tool to nuclear magnetic resonance spectroscopy

Metabonomics is a relatively new field of research in which the total pool of metabolites in body fluids or tissues from different patient groups is subjected to comparative analysis. Nuclear magnetic resonance (NMR) spectroscopy is the technology that is currently most widely used for the analysis of these highly complex metabolite mixtures, and hundreds of metabolites can be detected without any upfront separation. We have investigated in this study whether gas chromatography (GC) separation in combination with flame ionisation detection (FID) and mass spectrometry (MS) detection can be used for metabolite profiling from urine. We show that although GC sample preparation is much more involved than for NMR, hundreds of metabolites can reproducibly be detected and analysed by GC. We show that the data quality is sufficiently high--particularly if appropriate baseline correction and time-warping methods are applied--to allow for data comparison by chemometrics methods. A sample set of urines from eleven healthy human volunteers was analysed independently by GC and NMR, and subsequent chemometrics analysis of the two datasets showed some similar features. As judged by NIST database searches of the GC/MS data some of the major metabolites that are detected by NMR are also visible by GC/MS. Since in contrast to NMR every peak in GC corresponds to a single metabolite, the electron ionisation spectra can be used to quickly identify metabolites of interest if their reference spectra are present in a searchable database. In summary, we show that GC is a method that can be used as a complementary tool to NMR for metabolite profiling of urine samples.

Supported capillary membrane sampling-gas chromatography on a valve with a pulsed discharge photoionization detector

The objective of this study was to develop and evaluate a simple miniaturized approach to gas chromatography termed supported capillary membrane sampling-gas chromatography on a valve (SCMS-GCOV). The prototype instrument uses a pulsed discharge photoionization detector (PDPID) as the GC detector. Two different analyzers were constructed. The first used a bench scale SCMS-GC. The second was a miniaturized SCMS-GCOV analyzer. The SCMS-GCOV analyzer was used to monitor the concentrations of trihalomethanes (THM4) in drinking water. Details are given for the construction of the SCMS-GC-PDPID and the SCMS-GCOV-PDPID analyzers. The results of method detection limit, accuracy and precision studies are reported for analysis of THM4 and are compared to other methods of THM4 analysis. Side-by-side comparison studies are conducted between the SCMS-GCOV and USEPA 502.2 with promising results.

On-line monitoring of trihalomethane concentrations in drinking water distribution systems using capillary membrane sampling-gas chromatography

Trihalomethane concentrations are not typically monitored continuously in drinking water distribution systems. This means that data is not immediately available to operators so that they can make decisions that directly affect water quality. Monitoring data could be useful to researchers and operators who might want to better understand disinfection by-product formation and removal in their distribution systems. In this paper, a capillary membrane sampler (CMS), which uses a silicone membrane to directly sample trihalomethanes from a water sample, shows promise as a sampling device that can be used to introduce samples directly into a gas chromatograph for on-line monitoring. The construction, optimization, operation and evaluation of this capillary membrane sampling-gas chromatograph (CMS-GC) are discussed. The result of optimization, method detection limit, accuracy, precision and linearity studies are presented. Side-by-side studies have been done comparing the CMS-GC method to USEPA Method 502.2. While the CMS-GC method is not meant to replace USEPA Method 502.2, it does offer advantages for on-line monitoring and meets several of the criteria proposed as desirable for on-line monitoring of THM concentrations in drinking water distribution systems.

Measuring trihalomethane concentrations in water using supported capillary membrane sampling-gas chromatography

The objective of this study was to develop and evaluate a supported capillary membrane sampling-gas chromatography method for the analysis of trihalomethanes (THMs) in drinking water. The effects of experimental parameters, such as flow rate of carrier gas, water temperature, ionic strengths of solutions and transfer line temperature on the system performance were investigated. The results of method detection limit and accuracy and precision studies are reported.

A Simple, Inexpensive, and Reliable Method for Measuring Brønsted-Acid Site Densities in Solid Acids

A method based on amine decomposition has been developed for measuring the Bronsted-acid site densities using a standard, tubular reactor with an on-line gas chromatograph (GC). After exposing a sample to n-propylamine vapor and flushing it in flowing He at 473 K, the sample was ramped in flowing He to 773 K while trapping the products in the GC sample loop using liquid nitrogen. Site densities were determined from the quantity of propene formed by the decomposition of the n-propylammonium ions via the Hofmann-elimination reaction. The use of small amounts of sample was shown to be important for elimination of secondary products. The method was tested using H-ZSM-5, H-FER, H-MOR and H-Y zeolites, as well as a γ-Al2O3 sample, and shown to give essentially exact agreement with temperature-programmed desorption and thermogravimetric analysis measurements of n-propylamine performed in vacuum.

Purge-and-Trap Isothermal Multicapillary Gas Chromatographic Sample Introduction Accessory for Speciation of Mercury by Microwave-Induced Plasma Atomic Emission Spectrometry

A compact device based on purge-and-trap multicapillary gas chromatography was developed for sensitive species-selective analysis of methylmercury and Hg2+ by atomic spectrometry. The operating mode includes in situ conversion of the analyte species to MeEtHg and HgEt2 and cryotrapping of the derivatives formed in a 0.53-mm-i.d. capillary, followed by their flash (< 30 s) isothermal low-temperature separation on a minimulticapillary (22 cm) column. The very low detection limits obtained (0.01 pg mL-1 of Hg for methylmercury) are due to the narrow injection band and reduced peak broadening in a bundle of 0.038-mm capillaries at high flow rates (> 60 mL min-1) compatible with an MIP AES detector (no dilution with a makeup gas is required). Developments regarding each of the steps of the analytical procedure and effects of operational variables (sample volume, purge flow, trap temperature, separation conditions) are discussed. The device allows speciation of MeHg+ and Hg2+ down to 5 pg g-1 in urine and, after a rapid microwave-assisted hydrolysis, down to 0.1 ng g-1 in solid biological samples with a throughput of 6 samples/h. The analytical protocols developed were validated by the analysis of DORM-1 (dogfish muscle), TORT-1 (lobster hepatopancreas), and Seronorm urine certified reference materials.