On-line Gas Chromatography-mass Spectrometry Research Articles

Understanding Gas Permeation during High Pressure Operation of PEM Water Electrolyzers

Governments and industries across the world have initiated implementation of clean hydrogen (H2) to achieve zero emissions, yet significant challenges remain for large scale adoption. With the decreasing renewable electricity cost PEM water electrolyzers (PEMWEs) show significant potential for at scale deployment due to their high faradaic efficiency and high operating current density. To reduce the per kilogram price of hydrogen and increase the overall energy efficiency, PEMWEs need to be operated at high differential pressures (30 to 50 bar) to eliminate the need for compression during storage and transportation1. To achieve high faradaic efficiency, thinner membranes are required to reduce voltage losses within the cell. However, thinner membranes exhibit a higher gas permeation rate which leads to increased crossover of hydrogen from the cathode through the membrane to the anode. Such increased crossover of H2 not only reduces the efficiency but can also result in flammable gas mixtures (lower flammability limit for H2 in O2 is 4 %) as Iridium/Iridium oxide (anode catalyst) is inefficient in oxidizing H2 1. The addition of a gas recombination catalyst (GRC) to the membrane is an useful strategy to oxidize permeating H2 and minimize the H2:O2 ratio at the anode.In this study, a high pressure (up to 30 bar) electrolyzer setup is coupled with online gas chromatography-mass spectrometry to understand the H2 gas permeation in membranes as a function of H2 partial pressure and operating current density (simulated by varying the flow rates) as shown in Figure 1 . Effect of the GRC, its loading, and its location on the H2 permeation will be elucidated. Differences induced by the addition of anode and cathode catalyst layers on H2 permeation rates will also be presented.Figure 1. Ex-situ H2 permeation rate at different cathode operating pressure at 80 °C. The anode was maintained at 1 bar of O2 partial pressure Acknowledgement This research is supported by the U.S. Department of Energy (DOE) through the Hydrogen and Fuel Cell Technologies Office, program manager Dave Peterson Reference Bernt, M., Schröter, J., Möckl, M. & Gasteiger, H. A. Analysis of Gas Permeation Phenomena in a PEM Water Electrolyzer Operated at High Pressure and High Current Density. J. Electrochem. Soc. 167, 124502 (2020). Figure 1

High-Performance Lithium-Sulfur Batteries with Metal-Deposited Graphite Cathode and Lithium Polysulfide Catholyte

Lithium-sulfur (Li-S) batteries have attracted remarkable attention as next-generation batteries due to their low cost and high theoretical specific energy density.[1] However, it has encountered several difficulties, including low specific capacity due to the insulating nature of sulfur as well as poor cycle performance, which is caused by the dissolution of reaction intermediates (lithium polysulfide, LiPS) into the electrolyte. [2] Most strategies to overcome the above disadvantages are focused on designing carbon-based host materials, such as highly conductive and/or mesoporous carbon. [3] [4] However, it is difficult to completely suppress the dissolution of LiPS by the physical adsorption. Recent research thus focused on the utilization of chemical interactions between LiPS and electrode additive, mainly metal particles, to suppress the dissolution of LiPS. [5] Although it has been reported that the addition of metal improves the capacity retention and suppresses the self-discharge, the mechanistic understanding is still lacking.In this study, we selected Au and Ag as a metal additive, which has similar electrical conductivity but different affinity towards sulfur, to clarify the effect of metal-sulfur interaction on battery performances. We selected catholyte, in which LiPS (Li2S8) was previously dissolved, was selected as an electrolyte to achieve a continuous supply of LiPS to the positive electrode. Galvanostatic charge-discharge measurements revealed that the charge/discharge capacity affected by the metal addition; 75.8 mAh cm-3 (G) < 77.4 mAh cm-3 (Ag/G) < 99.5 mAh cm-3 (Au/G), with excellent initial discharge capacity for Au-decorated electrode. Furthermore, we confirmed the effect of the amount of metal additive on the charge/discharge capacity. The result thus indicates (1) addition of metal with a strong affinity towards sulfur and (2) optimization of its amount is crucial to improve Li-S battery performances. The improvement in capacity retention rate was confirmed for the metal-decorated electrode; capacity retention at the 20th cycle was G = 68.1 % < Ag = 89.3 % < Au = 94.9 %. The interaction between the metal additives and LiPS may contribute to anchor LiPS at the vicinity of the electrode, leading the improvement in the cyclability.The reason for the improvement in the cyclability will be discussed based on the surface product analysis of the electrode after initial charge and discharge, as deduced from on-line gas chromatography-mass spectrometry (GC-MS) measurements. We will also discuss the effect of metal additives on the reaction mechanism of sulfur redox reaction by in situ probing of the reaction intermediates using infrared spectroscopy. Elucidation of the reaction mechanism opens up the new avenue to optimize both electrode and electrolyte materials, which can further improve the performance of the Li-S battery technology.[1] Richard, V. N, Nature, 2014, 507, 26-28.[2] Hailiang, W. et al. Nano Lett. 2011, 11, 2644-2647.[3] Kunpeng, C. et al. Nano Lett. 2012, 12, 6474-6479.[4] Jorg, S. et al. Angew. Chem. Ed. 2012, 51, 3591-3595.[5] Chao-Ying, F. et al. ACS Appl. Mater. Interfaces, 2015, 7, 27959-27967.

Stir bar sorptive extraction and automatic two-stage thermal desorption-gas chromatography-mass spectrometry for trace analysis of the byproducts from diphenyl carbonate synthesis

In this study, a fast and sensitive method based on stir bar sorptive extraction (SBSE) and two-step thermal desorption coupled with online gas chromatography-mass spectrometry was established to simultaneously analyse six trace byproducts [phenyl salicylate (PS), xanthone (XA), methyl o-hydroxybenzoate (MS), 2-methyl diphenyl carbonate (PTC), methyl o-methoxybenzoate (MSME) and phenyl o-methoxybenzoate (PSME)] generated in the process of diphenyl carbonate (DPC) synthesis. Analytes were enriched with multiple sorptive stir bars simultaneously, followed by thermal desorption, cryo-focusing, and instantaneous injection, effectively solving such problems as long adsorption time and small sample volumes compared with conventional stir bars. The main factors influencing SBSE and thermal desorption were studied. Optimized stir bar extraction conditions are as follows: the volume fraction of methanol is 10%, the extraction time is 6 min, and the stirring rate is 1200 rpm at room temperature (25 °C). Optimized two-step thermal desorption conditions are as follows: in the first desorption step, the desorption temperature is 300 °C, the desorption time is 10 min, and the valve and transmission line temperature is 200 °C; in the second desorption step, the cold trap temperature is −10 °C, which is increased at a rate of 100 °C/s to 320 °C and held for 5 min. A splitless mode and a split mode with a split ratio of 20:1 are used in the first and the second desorption step, respectively. Under the optimal conditions, the six byproducts generated in the synthesis of DPC via transesterification were quantitatively analyzed by external standard method. The results showed that, within the range of 1.0−100 ng/L for all of the six transesterification byproducts, this method revealed good linearity with correlation coefficients (r) ≥0.997. The limits of detection (LODs) were between 0.054 ng/L and 0.253 ng/L, the relative standard deviations (RSD) were from 5.2% to 11.5%, and the recoveries were 81.6%−102.6% (n = 3). The method is simple, rapid and has a wide linear range, high accuracy, and sensitivity, as well as good stability. It is suitable for simultaneous, rapid and selective analysis of six trace byproducts in the process of DPC synthesis. It can also provide vigorous data support and industrialization guidance for the selection of transesterification conditions and research on the formation mechanisms, distribution regularity, and even control of transesterification byproducts.

A comparison of fast and reactive pyrolysis with insitu derivatisation of fructose, inulin and Jerusalem artichoke (Helianthus tuberosus)

Reactive pyrolysis is a technique that provides mechanistic information by performing pyrolysis of the substrate in a sealed glass capsule at elevated temperature and pressure for relatively long time. This technique has already shown great potential for the analysis of biomass, favouring the formation of only the most thermostable compounds. In this work, both fast and reactive pyrolysis with on-line gas chromatography-mass spectrometry analysis (Py-GC/MS) are used to study fructose, inulin and Jerusalem artichoke tubers (Heliantus tuberosus). Interesting differences were found between the two systems, and became even more evident as the reaction time was increased. The most striking result was the formation of di-fructose dianhydrides (DFAs), a class of compounds with interesting biological activities. DFAs were obtained in high yields from reactive pyrolysis, but not from fast pyrolysis. Hypotheses on the pyrolysis mechanisms were made based upon the composition of the pyrolysates. This work describes for the first time the behaviour of fructans under reactive pyrolysis.

Determination of parabens in human urine by optimal ultrasound-assisted emulsification microextraction and on-line acetylation gas chromatography-mass spectrometry.

An effective and solvent-less method for the rapid determination of four commonly detected parabens (methyl-, ethyl-, propyl- and butyl-) in human urine samples is described. This method employed ultrasound-assisted emulsification microextraction (USAEME) before identification and quantitation of the parabens via on-line acetylation gas chromatography-mass spectrometry (GC-MS). Urine samples were enzymatically de-conjugated with β-glucuronidase and then extracted by an optimal USAEME procedure for the measurement of total concentrations of target analytes. The optimal USAEME parameters for one mL of urine sample (containing 0.1-g of sodium chloride), according to the Box-Behnken design method, are thus described: extractant of 200-μL of ethyl acetate, and ultrasonication for 1.0min and centrifugation at 7000rpm (3min). The supernatant was collected and evaporated until dry. Then the residue was re-dissolved in methanol (100-μL), and the extract was subjected to on-line acetylation GC-MS analysis. The limits of quantitation (LOQs) were less than 0.06ng/mL. Precisions for both intra- and inter-day analysis were calculated, and were less than 8%. Mean extraction recovery (known as trueness) was between 83 and 101% on three concentration levels. In human urine, the total concentrations of the four selected parabens, according to preliminary results, range from 0.3 to 124.5ng/mL for male, and from 27.2 to 246.3ng/mL for female. Female urine samples showed higher concentrations for the target parabens, which may indicate higher exposure due to lifestyle. This method permits accurate and high-throughput analysis of parabens for epidemiological studies.

Novel and rapid method for determination of organophosphorus pesticide residues in edible fungus using direct gas purge microsyringe extraction coupled on-line with gas chromatography–mass spectrometry

In this work a new analytical method for a rapid and simultaneous determination of 28 organophosphorus pesticides (OPPs) residues in edible fungus using gas purge microsyringe extraction (GP-MSE), coupled with on-line gas chromatography–mass spectrometry (GP-MSE-GC-MS) has been developed and optimized. GP-MSE, a novel gas flow liquid-phase microextraction technique, has been then fruitfully used as innovative and one-step extraction procedure, allowing a direct injection into the gas chromatograph coupled with a mass spectrometry detector (GC–MS) system without any further cleaning step. Once optimized, the GP-MSE-GC-MS analysis procedure showed reproducibility values, resolutions, linear responses, detection and quantification limits that allowed to consider this method suitable for the analysis of the 28 OPPs in real samples. Furthermore, OPP recoveries and the relative standard deviations (RSDs) ranged from 85.26% to 100.21%, and from 1.6% to 6.9%, respectively. This procedure was then used for the analysis of real samples and the obtained results were compared with those of ultrasonic extraction–solid phase extraction. Among the 28 OPPs, 14 of them were found in Lentinus edodes and Enoki mushrooms fungus samples, with a total concentrations of 112.7 and 210.7μgkg−1, respectively. This work demonstrated then that GP-MSE-GC-MS provided a highly efficient, solvent-saving, accurate and sensitive quantitative analysis method for a rapid determination of OPPs in edible fungus.

Online coupling lab on valve-dispersive liquid–liquid microextraction-multisyringe flow injection with gas chromatography-mass spectrometry for the determination of sixteen priority PAHs in water

Online gas chromatography-mass spectrometry determination of priority PAHs in water.

Optimum Yields of Dibenzylbutyrolactone‐type Lignans from Cynareae Fruits, During their Ripening, Germination and Enzymatic Hydrolysis Processes, Determined by On‐line Chromatographic Methods

Dibenzylbutyrolactone-type lignans are the physiologically active constituents of the achene fruits of Cynareae. These lignans occur in glycoside/aglycone forms: in the highest quantity of the arctiin/arctigenin, matairesinoside/matairesinol and tracheloside/trachelogenin pairs found in the fruits of Arctium lappa L., Centaurea scabiosa L. and Cirsium arvense (L.) Scop. To optimise the extraction yield of the arctiin/arctigenin, matairesinoside/matairesinol and tracheloside/trachelogenin glycoside/aglycone pairs, from the fruits of Arctium lappa, Centaurea scabiosa and Cirsium arvense, under the ripening, germination and enzymatic hydrolysis processes of the fruits. Identification and quantification of lignans were performed with on-line gas chromatography-mass spectrometry (GC-MS) and with high performance liquid chromatography (HPLC), both with UV and mass selective detections (HPLC-UV/MS). As novelties to the field it was confirmed that: (i) the unripe fruits provide a high amount of lignans, similar to the ripe fruit; (ii) the fruits of Arctium lappa and Cirsium arvense do have glycosidase activity to hydrolyse their lignan glycosides into free lignans; (iii) the glycosidase of Centaurea scabiosa fruit becomes activated under its germination process only; and (iv) the overwhelming part of the fruits lignan contents (80-94%) in all three species are accumulated in the embryo. The best sources of (i) lignan aglycones are the enzyme-hydrolysed embryos, separating spontaneously during the germination process, and (ii) lignan glycosides are the unripe fruits.

The use of MSSV pyrolysis to assist the molecular characterisation of aquatic natural organic matter

Microscale sealed vessel pyrolysis (MSSVpy) with online gas chromatography mass spectrometry (GC–MS) was used with several other established and complementary analytical methods to robustly characterize the structure of aquatic natural organic matter (NOM) and to practically assess the analytical value of MSSVpy. The NOM used in the study was from North Pine (NP) reservoir, which is one of the major source waters supplying Brisbane, the capital city of the Australian state of Queensland. The reservoir has moderate dissolved organic carbon (DOC; 5 mg L −1) levels and is impacted by algae which periodically occur in bloom proportions. The hydrophobic (HPO; 65% initial DOC) and transphilic (TPI; 12%) fractions showed H/C values >1, low UV abs and low aryl-C measured by NMR which are all indicative of low aromaticity. MSSVpy produced distinctly higher product concentrations than traditional flash pyrolysis and the molecular profile of the HPO and TPI fractions revealed by MSSVpy was correlated with the other analytical data to help establish their structural relevance. Prolific distributions of alkyl substituted aromatic (e.g., benzenes, naphthalenes) and hydroaromatic (e.g., tetralins) products detected in the HPO fraction were attributed to the aromatisation of terpanes and other aliphatic compounds from algal, and possibly also plant sources. Alkyl phenols also detected in HPO in high abundance, are probably from algal biopolymers, but may also reflect a contribution from non-methoxylated lignin units of catchment grasses. There was no analytical evidence of the dihydroxy or methoxy aromatic structures typical of wood lignin or tannin. N-organic pyrolysates (e.g., alkyl pyrroles, pyridines, indoles) of diagenetically altered proteins were concentrated in the TPI fraction. The quantitative importance of the N-organic moiety of the TPI fraction was corroborated by a low C/N ratio and distinctive amide and amine signals detected by 13C NMR and FTIR. This integrated study demonstrates that the qualitative speciation provided by MSSVpy can make a significant contribution to the structural characterisation and source recognition of aquatic NOM.

Release of lipoxygenase products and monoterpenes by tomato plants as an indicator of Botrytis cinerea‐induced stress

Changes in emission of volatile organic compounds (VOCs) from tomato induced by the fungus Botrytis cinerea were studied in plants inoculated by spraying with suspensions containing B. cinerea spores. VOC emissions were analysed using on-line gas chromatography-mass spectrometry, with a time resolution of about 1 h, for up to 2 days after spraying. Four phases were delimited according to the starting point and the applied day/night rhythm of the experiments. These phases were used to demonstrate changes in VOC flux caused by B. cinerea infestation. Tomato plants inoculated with B. cinerea emitted a different number and amount of VOCs after inoculation compared to control plants that had been sprayed with a suspension without B. cinerea spores. The changes in emissions were dependent on time after inoculation as well as on the severity of infection. The predominant VOCs emitted after inoculation were volatile products from the lipoxygenase pathway (LOX products). The increased emission of LOX products proved to be a strong indicator of a stress response, indicating that VOC emissions can be used to detect plant stress at an early stage. Besides emission of LOX products, there were also increases in monoterpene emissions. However, neither increased emission of LOX products nor of monoterpenes is specific for B. cinerea attack. The emission of LOX products is also induced by other stresses, and increased emission of monoterpenes seems to be the result of mechanical damage induced by secondary stress impacts on leaves.

Determination of flavour and off-flavour compounds in orange juice by on-line coupling of a pervaporation unit to gas chromatography–mass spectrometry

A method for the analysis of several volatiles compounds responsible for orange juice flavour (ethyl butanoate, limonene, linalool, α-pinene, geranial, neral and α-terpineol) has been developed. The isolation of this compounds was carried out by pervaporation (PV) followed by on-line gas chromatography–mass spectrometry (GC–MS). The coupling PV–GC–MS has been successfully applied to fresh hand-squeezed orange juices and frozen concentrated ones in order to establish differences in their flavour profile. Method has been validated with recovery spike experiments which showed its applicability for a wide range of concentrations.

Effect of oxygen addition on polycyclic aromatic hydrocarbon formation in 1,3 butadiene counter-Flow diffusion flames

The effect of 3% O 2 addition to the fuel on detailed chemical structure of a 1,3 butadiene counter-flow diffusion flame has been investigated by using heated microprobe sampling and online gas chromatography mass spectrometry. Centerline gas temperature and species mole-fraction profiles were measured both in the absence and presence of oxygen on the fuel side. The rapid thermocouple insertion method was used to obtain the flame temperature profiles. Although the addition of oxygen to the fuel side did not significantly change the shape and peak values of the temperature profiles, species mole-fraction profiles were significantly altered. Flame reactions started earlier in the presence of oxygen in the fuel, resulting in the shift of the reaction zone toward the fuel burner port. The presence of oxygen in the fuel led to decreased peak mole fractions of the aromatic and two-ring polycyclic aromatic hydrocarbon species. In contrast, the peak mole fractions of polycyclic aromatic hydrocarbon having three or more rings significantly increased in the presence of oxygen in the fuel stream. An analysis of the data suggests the need to invoke new reaction mechanisms describing the formation and destruction of polycyclic aromatic hydrocarbon.

Analysis of steroids XXXIX. Estimation of the impurity profile of 5α-androst-2-ene-17-one

The impurity profile of 5α-androst-2-ene-17-one was investigated by using two different capillary gas chromatographic (GC) and a reverse phase high performance liquid chromatographic systems (HPLC). The impurities were identified by retention matching with authentic standards, diode-array UV spectroscopy, on-line gas chromatography-mass spectrometry (GC-MS), off-line HPLC-MS and NMR spectroscopy. The following impurities were identified and quantitated: ring A saturated, isomeric (1-ene, 3-ene, 4-ene, 5-ene) analogues, 3α and 3β-hydroxy as well as 3β-phenyl derivatives.