Publications
Read peer-reviewed articles featuring the Polyarc and Jetanizer.
2019
Beaumier, E. et al., ACS Catalysis, “Carbodiimide Synthesis via Ti-Catalyzed Nitrene Transfer from Diazenes to Isocyanides”
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Simple Ti imido halide complexes such as [Br2Ti(NtBu)py2]2 are competent catalysts for the synthesis of unsymmetrical carbodiimides via Ti-catalyzed nitrene transfer from diazenes or azides to isocyanides. This is the only example of catalytic nitrene transfer to isocyanides where diazenes have been employed as the nitrene source. Both alkyl and aryl isocyanides are compatible with the reaction conditions, although product inhibition with sterically unencumbered substrates sometimes limits the yield when diazenes are employed as the oxi-dant. The reaction mechanism has been investigated both experimentally and computationally, wherein a key feature is that product release is triggered by electron transfer from an η2-carbodiimide to a Ti-bound azobenzene. This ligand-to-ligand redox buffering obviates the need for high-energy formally TiII intermediates, and provides further evidence that substrate and product “redox noninnocence” can promote unusual Ti redox catalytic transformations.
Peterson, B. et al., ASC Sustainable Chemistry & Engineering, “Catalytic Hot-Gas Filtration with a Supported Heteropolyacid Catalyst for Preconditioning Biomass Pyrolysis Vapors”
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During ex situ catalytic fast pyrolysis (CFP) of biomass, the separation of reactive char and alkali/alkaline particulates from biomass pyrolysis vapors by hot-gas filtration (HGF) leads to improved vapor stability and quality. HGF in tandem with chemical tailoring (e.g., partial deoxygenation) of the clean pyrolysis vapors, denoted as catalytic hot-gas filtration (CHGF), has the potential to further improve vapor composition by removing reactive oxygen moieties and protect downstream upgrading catalysts from fouling. Downstream upgrading refers to both vapor phase upgrading (e.g., ex situ CFP) and condensed phase upgrading (e.g., hydrotreating). Consequently, CHGF (as a single unit operation) was evaluated for preconditioning pyrolysis vapors for downstream upgrading processes. In order to understand the effective operating conditions that successfully filter and partially deoxygenate pyrolysis vapors, a titania-supported molybdenum heteropolyacid (Mo-HPA/TiO2) catalyst was studied for use in CHGF. Here, pine pyrolysis vapors were generated in a small pilot-scale pyrolyzer and transferred to a CHGF unit via a continuous-flow slipstream. In the CHGF unit, the pyrolysis vapors were filtered and upgraded over a packed Mo-HPA/TiO2 catalyst bed. Real-time monitoring and identification of the products formed was achieved by molecular beam mass spectrometry. The results showed that under a hydrogen-rich environment, the pine vapors were partially deoxygenated and alkylated over the Mo-HPA/TiO2 catalyst. Reactivity studies revealed that an increase in hydrogen concentration and a reduction in weight-hourly space velocity enhanced deoxygenation and alkylation. Time-on-stream (TOS) studies showed stable product formation up to 1 h with little change in catalyst activity. Additionally, the liquid product was collected using a custom fractional condensation unit (built in-house) and analyzed by gas chromatography mass spectrometry to confirm that the product was partially deoxygenated and alkylated. The combination of CHGF and fractional condensation allowed for chemical and physical removal of both foulant and value-added compounds (e.g., phenols, alkylphenols, methoxyphenols, cyclopentenones) for additional enhancement of downstream upgrading processes. The pre- and post-reaction catalysts were characterized using temperature programmed desorption, N2 physisorption, and elemental analysis with results indicating some catalyst coking. A hydrogen-based catalyst regeneration procedure restored the reacted catalyst activity to that of fresh Mo-HPA/TiO2.
Luong, J. et al., Journal of Chromatography, “Post-Column Reaction with a 3D-Printed Two-Stage Microreactor and Flame Ionization Detection for Carbon Compound Independent Response in Fast Gas Chromatography”
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Fast gas chromatography that leverages the high chromatographic efficiency of narrow bore capillary column technology and temperature programming was successfully integrated with a third-generation low void-volume, 3D-printed two-stage microreactor. Effective management of extra-column effect and the capability to perform post-column backflushing were achieved with the incorporation of a recently commercialized, electronically controlled pneumatic switching device and a deactivated metal three-way microdevice. With this configuration, narrow bore capillary columns having internal diameters between 100 µm to 150 µm can be employed to produce chromatographic peaks in the domain of fast gas chromatography, with peak widths at half-height ranging from 0.42 s to 0.92 s for probe compounds having k’ over a range from 1.7 for toluene to 60 with the last analyte (nC44) eluted in less than 12 min. The carbon independent response capability of the 3D-printed microreactor affords unique and advantaged differentiators, for instance, conducting measurement of the target analytes using one single carbon-containing compound for calibration with an acceptable accuracy of ±10%, achieving a higher degree of accuracy by eliminating the need for multi-level and multi-compound calibration, and improving sensitivity for compounds that are not efficiently ionized by flame ionization detection. Using this platform, repeatability of retention times for 14 probe compounds was less than 0.1 % RSD (n = 10), and less than 1.0 % RSD (n = 10) for area counts. The utility of the analytical approach was illustrated with relevant, challenging applications.
Luong, J. et al., Analytical Chemistry, “Uniformity and Sensitivity Improvements in Comprehensive Two-Dimensional Gas Chromatography using Flame Ionization Detection with Post-Column Reaction”
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A 3D-printed microreactor for post-column reaction was successfully integrated with comprehensive two-dimensional gas chromatography. A two-stage post-column reaction provided carbon independent response, it enhanced flame ionization detection uniformity, and it improved detector sensitivity. These enhancements are critical to overcome challenges in analyses using comprehensive two-dimensional gas chromatography and flame ionization detection, which aim to separate and quantify multiple components. Post-column reaction flame ionization detection eliminated the requirement of multi-level and multi-compound calibration, it enabled determination of target analytes with a single carbon-containing calibration compound with an accuracy of ±10%, and it improved sensitivity for compounds that were not efficiently ionized by flame ionization detection. Extra column band-broadening caused by the incorporation of the 3D-printed microreactor was minimized using optimized reactor operating parame-ters and inter-column connectivity. Chromatographic fidelity was in the practical domain of comprehensive two-dimensional gas chromatography. Typical peak widths at half-height using the described approach ranged from 165 ms to 235 ms for probe com-pounds with retention factors spanning 5 < k < 40.
Luong, J. et al., Journal of Separation Science, “Metal 3D‐printed catalytic jet and flame ionization detection for in situ trace carbon oxides analysis by gas chromatography”
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A gas chromatographic approach for the determination and quantification of trace levels of carbon oxides in gas phase matrices for in situ or near‐line/at‐line analysis has been successfully developed. Catalytic conversion of the target compounds to methane via the methanation process was conducted inside a metal 3D‐printed jet that also acted as a hydrogen burner for the flame ionization detector. Modifications made to a field transportable gas chromatograph enabled the leveraging of advantaged microfluidic‐enhanced chromatography capability for improved chromatographic performance and serviceability. The compatibility with adsorption chromatography technology was demonstrated with in‐house constructed columns. Sustained reliable conversion efficiencies of greater than 99% with respectable peak symmetries were attained at 400°C. Quantification of carbon monoxide and carbon dioxide at a parts‐per‐million level over a range from 0.2 ppm to 5% v/v for both compounds with a respectable precision of less than 3% relative standard deviation for peak area (n = 10) and a detection limit of 0.1 ppm v/v was achieved. Linearity with correlation coefficients of R2 greater than 0.9995 and measured recoveries of >99% for spike tests were achieved. The 3D‐printed steel jet was found to be reliable and resilient against potential contamination from the matrices owing to the in situ backflushing capability.
Reiner, B. et al., Journal of Inorganic Chemistry, “Group 4 Diarylmetallocenes as Bespoke Aryne Precursors for Titanium-Catalyzed [2 + 2 + 2] Cycloaddition of Arynes and Alkynes”
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Despite the ubiquity of reports describing titanium (Ti)-catalyzed [2 + 2 + 2] cyclotrimerization of alkynes, the incorporation of arynes into this potent manifold has never been reported. The in situ generation of arynes often requires fluoride, which instead will react with the highly fluorophilic Ti center, suppressing productive catalysis. Herein, we describe the use of group 4 diarylmetallocenes, CpR2MAr2 (CpR = C5H5, C5Me5; M = Ti, Zr), as aryne precursors for the Ti-catalyzed synthesis of substituted naphthalenes via coupling with 2 equiv of an alkyne. Fair-to-good yields of the desired naphthalene products could be obtained with 1% catalyst loadings, which is roughly an order of magnitude lower than similar reactions catalyzed by palladium or nickel. Additionally, naphthalenes find broad applications in the electronics, photovoltaics, and pharmaceutical industries, urging the discovery of more economic syntheses. These results indicate that aryne transfer from a CpR2M(η2-aryne) complex to another metal is a viable route for the introduction of aryne fragments into organometallic catalytic processes.
Filgueira, M. et al., Journal of Chromatography A, “High-throughput Analytical Approach Combining Automated Sample Preparation and Gas Chromatography with Universal Carbon Response”
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Specifying effective analytical techniques and methods can be very challenging when a large number of sample streams need to be analyzed with high frequency. Combining those requirements with the need to monitor multiple components over a wide range of concentrations makes at-line analytical approaches preferred by many analytical scientists. Traditionally, at-line analytical support requires sample preparation and operator time. Recently developed technologies enabled automated sample preparation tools coupled with gas chromatography; thus, eliminating sample preparation steps and increasing productivity. Recently a commercial micro-reactor was introduced that can be combined with a flame ionization detector, providing the ability to quantify components without the need to perform a standard calibration, which saves significant time and materials. In this manuscript, we describe a unique analytical capability that combines automated sample preparation and gas chromatography with flame ionization detection and universal carbon response to provide high flexibility and accuracy when there is minimal information about the unknowns or reference materials are not available. Some of the challenges and performance monitoring techniques for this technology are also discussed in this manuscript.
Yee, G. et al., Organometallics, “Mechanistic Study of Palladium-Catalyzed Hydroesterificative Copolymerization of Vinyl Benzyl Alcohol and CO”
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The copolymerization of vinyl benzyl alcohol (VBA) and carbon monoxide (CO) to give a new polyester poly(VBA-CO) has been achieved via palladium-catalyzed hydroesterification. Reaction conditions involve moderate temperatures, moderate to low CO pressures, and low catalyst loadings to give a low molar mass (Mn ∼ 3–4 kg/mol) polymer as a ∼2:1 mixture of linear to branched repeat units. The polymer molar mass increase is consistent with a step-growth polymerization mechanism, and ester yields of >97% are achieved within 24 h. However, increases in Mn cease beyond 16 h. Control experiments indicate that the degree of polymerization is limited due to a combination of side reactions such as alcoholic end-group oxidation, hydroxycarbonylation, and alcohol acetylation, which lead to the degradation of monomeric and polymeric end groups. When a less promiscuous substrate is used such as 10-undecenol, higher molar masses (Mn ∼ 16 kg/mol) are achieved. This method has the potential to be a mild route to new polyester architectures with appropriate mitigation of side reactions.
Tobias, H. et al., Analytical Chemistry, “Low Temperature Catalytic Combustion Reactors for High Precision Carbon Isotope Measurements in Gas Chromatography Combustion Isotope Ratio Mass Spectrometry”
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Metal oxide-filled reactors constructed with ceramic tubes or fused silica capillary are widely used for combustion in gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). However, they tend to be easily cracked or broken and prone to leaks at operating temperatures of ∼950 °C. Here we introduce a modified commercially available catalytic combustion/reduction methanizer to quantitatively convert organics to CO2 for δ13C analysis while retaining chromatographic resolution. These modified “ARC” reactors operate with a transition-metal catalyst that requires a flowing O2 gas to enable complete conversion to CO2 at lower temperature (620 °C) with acceptable reactor life, reduced complexity, and improved robustness. Performance of two versions of the ARC reactors with different combustion volumes was characterized by analysis of steroid and alkane isotopic standard materials. Linearity of steroid isotopic standards ranged from 0.02 to 0.60 ‰/V in the range of 25 to 200 ng of each steroid injected. Precisions and accuracies of measurements for steroids and alkanes had average standard deviations of SD(δ13C) less than ±0.18 ‰ and average accuracy of better than 0.19 ‰ δ13CVPDB. Peak width expansion within both devices were similar to that in traditionally used metal oxide reactors. These data demonstrate for the first time that novel combustion schemes enable operation at lower temperatures as an alternative approach comparable to high temperature techniques to yield high precision δ13C data with GCC-IRMS.
2018
Moldoveanu, S. et al., Gas Chromatography, “Derivatization Methods in GC and GC/MS”
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The first part of this chapter presents the main objectives for performing derivatization of a sample to be analyzed by gas chromatography (GC) or gas chromatography/mass spectrometry (GC/MS). The derivatization is typically done to change the analyte properties for a better separation and also for enhancing the method sensitivity. In GC/MS, derivatization may improve the capability of compound identification. Examples illustrating such improvements are included. The second part describes several types of derivatization that are more frequently used in analytical practice. These include alkylation (e.g., methylation), formation of aryl derivatives, silylation (e.g., formation of trimethylsilyl derivatives), acylation (e.g., reactions with acyl chlorides or with chloroformates), and several other types of derivatizations. The chapter also presents typical derivatizations for analytes with specific functional groups and discusses artifact formation in certain derivatization reactions.
Luong, J. et al., Analytical Methods, “Post-Column Reaction Gas Chromatography with a Dual-Stage Microreactor for the Determination of Volatile Oxygenated Compounds in High-Pressure Liquefied Hydrocarbons”
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A reliable and practical approach for the direct measurement of volatile oxygenated compounds in high pressure liquefied light hydrocarbons has been successfully developed. The approach incorporates the use of a pressurized liquid injection device for sample introduction, a highly selective and polar ionic sorbent column technology to achieve separation of the targeted oxygenated compounds, and the augmentation of a recently commercialized dual-stage post column microreactor to convert carbon compounds; first to carbon dioxide by combustion and subsequently to methane by methanation. This two-stage conversion strategy is highly advantageous as it enables carbon compound independent response as well as sensitivity improvements, particularly for short-chain oxygenated compounds. Oxygenated compounds such as acetaldehyde, propionaldehyde, methanol, ethanol, iso-propanol, n-propanol, and acetone in light hydrocarbons were found to have respectable linear ranges from 0.1 ppm (v/v) to 3,000 ppm (v/v) with R2 greater than 0.997 and a relative precision of less than 10% RSD (n = 7). With the incorporation of carbon compound independent response capability, one single carbon-containing compound can be used for calibration to measure any of the target analytes with a respectable accuracy of less than ±10% error. The unique feature of carbon equimolar response also enables the possibility of determining a “total” concentration for the known volatile oxygenated compounds. As well, the need for multi-level calibration was eliminated over the range of interest. This novel concept enables new measurement capability and flexibility, enhances analytical throughput, and substantially decreases the overall cost of ownership. The utility of the methodology was demonstrated with practical industrial applications.
Hwang, A. et al., Journal of Catalysis, “Mechanistic study of methylbenzene dealkylation in methanol-to-olefins catalysis on HSAPO-34”
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Methylbenzenes entrained within the cavities of silicoaluminophosphate zeotype HSAPO-34 react with methanol in H+-mediated dealkylation to give ethylene and propylene in methanol-to-olefins catalysis. Methylbenzenes dealkylation on solid acids is proposed to occur either via the side-chain mechanism, where an exocyclic CC undergoes successive methylation prior to CC cleavage for olefin elimination, or the paring mechanism, where ring contraction to a bicyclohexenyl cation precedes CC cleavage for olefin elimination. Distinct dealkylation mechanisms prescribe distinct combinations of C atoms—from aromatic methyl, aromatic ring, and methanol/dimethyl ether—to comprise the olefin product. Site-specific isotope tracing that distinguishes between isotope labels in aromatic methyl and aromatic ring positions for each methylbenzene shows that tetramethylbenzene gives ethylene via the side-chain mechanism and penta- and hexamethylbenzene give propylene via the paring mechanism. The ratio of propylene selectivity to ethylene selectivity increases in methanol reactions on HSAPO-34 entrained with a distribution of methylbenzenes deliberately manipulated towards increasing fractions of penta- and hexamethylbenzene, corroborating the conclusion that aromatic precursors and dealkylation mechanisms for ethylene diverge from those for propylene.
Luong, J. et al., Analytical Chemistry, “Gas Chromatography with In-situ Catalytic Hydrogenolysis and Flame Ionization Detection for the Direct Measurement of Formaldehyde and Acetaldehyde in Challenging Matrices”
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A gas chromatographic strategy to advance the direct detection and quantification of volatile aliphatic aldehydes such as formal-dehyde and acetaldehyde in gas phase matrices without the need for sample pre-treatment or concentration has been successfully developed. The catalytic hydrogenolysis of aldehydes to alkanes is conducted in-situ within the 3D printed steel jet assembly of the flame ionization detector and without any additional hardware required. Reliable conversion efficiencies of greater than 90% with respectable peak symmetries for the analytes were attained at 400 °C. Quantification of formaldehyde and acetaldehyde at parts-per-million level over a range of 0.5-300 ppm (v/v) for formaldehyde and 0.2-430 ppm (v/v) for acetaldehyde with a respect-able precision of less than 5% RSD (n = 10) was achieved. Total analysis time is less than 10 min. Linearity with a correlation coef-ficient of R2 greater than 0.9997 and measured recoveries of >99% for spike tests under the specified conditions were achieved. The 3D printed steel jet assembly was found to be reliable and resilient to matrices such as air, water, hydrocarbons, and aromatics. An additional benefit realized with this analytical strategy is that the slight restriction induced by the presence of the catalyst in the 3D printed jet assembly enables backflush via the inlet split vent without the need for additional pressure control and inter-column connection devices. The utility of this technique was demonstrated with important aldehyde applications from various segments.
Dong, T. et al., RCS Advances, “Co-production of fully renewable medium chain α-olefins and bio-oil via hydrothermal liquefaction of biomass containing polyhydroxyalkanoic acid”
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Medium chain-length linear α-olefins (mcl-LAO) are versatile precursors to commodity products such as synthetic lubricants and biodegradable detergents, and have been traditionally produced from ethylene oligomerization and Fischer–Tropsch synthesis. Medium chain-length polyhydroxyalkanoic acid (mcl-PHA) can be produced by some microorganisms as an energy storage. In this study, Pseudomonas putida biomass that contained mcl-PHA was used in HTL at 300 °C for 30 min, and up to 65 mol% of mcl-PHA was converted into mcl-LAO. The yield and quality of the bio-oil co-produced in the HTL was remarkably improved with the biomass rich in mcl-PHA. Experiments with extracted mcl-PHA revealed the degradation mechanism of mcl-PHA in HTL. Overall, this work demonstrates a novel process to co-produce mcl-LAO and bio-oil from renewable biomass.
Patil, V. et al., Bioresource Technology, “Co-pyrolysis of lignin and plastics using red clay as catalyst in a micro-pyrolyzer”
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In the current study, low-density polyethylene and polystyrene were co-pyrolyzed with dealkaline lignin in a micro-reactor at 500°C with and without low-cost red clay catalyst. The products were analyzed with GC-MS/FID to quantify phenolic compounds, alkanes and alkenes. The synergistic effect between plastics and lignin was studied by comparing the carbon yield of compounds from co-pyrolysis with that from individual pyrolysis. The co-pyrolysis of lignin and polystyrene was also performed at 600, 700 and 800°C to examine the effect of pyrolysis temperature. The study explores a novel approach to enhance lignin depolymerization with red clay catalyst while utilizing waste plastics.
Bai, L., et al., Journal of Separation Science, “Complex mixture quantification without calibration using gas chromatography and a comprehensive carbon reactor in conjunction with flame ionization detection”
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Quantification of complex carbon‐containing mixtures are typically very time‐intensive tasks 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 evenly converting all carbon atoms to methane 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 confirm 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.
Pollo, B., et al., Trends in Analytical Chemistry, “The Impact of Comprehensive Two-Dimensional Gas Chromatography on Oil & Gas Analysis: Recent Advances and Applications in Petroleum Industry”
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Comprehensive two-dimensional gas chromatography (GC×GC) has impacted the workflow of GC-based methods used in petroleum industry. Application of GC×GC to petroleomic investigations have guided sample preparation to faster, cleaner, and more reliable formats. For instance, solvent consumption has been drastically reduced when using miniaturized devices in routine applications. Furthermore, flow-modulation has enabled cost-effective analysis and powerful separations of gases, fuels, and crude oils. Hyphenation of GC×GC to conventional and high resolution mass spectrometry has enabled the detection and identification of hundreds of compounds in a single analysis. Pixel-based methods enabled efficient handling of big data generated by GC×GC in forensic and geochemical investigations. This review has highlighted an ever-growing demand for modern and powerful analytical methods for oil & gas industry. Here, we described the most recent advances to sample preparation, GC×GC instrumentation, and multivariate data analysis in petroleum industry, including microextractions, high temperature GC×GC, and pixel-based data analysis.
Luong, J., et al., Analytical Methods, “In-situ Methanation with Flame Ionization Detection for the Determination of Carbon Dioxide in Various Matrices”
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An analytical technique that employs in-situ methanation with flame ionization detection for the measurement of carbon dioxide in various matrices has been developed and implemented. The methanation of carbon dioxide to methane is conducted in-situ within the 3D printed jet of the flame ionization detector without any additional hardware required. Quantification of carbon dioxide at the parts-per-million level over a range of 1-10,000 ppm (v/v) with respectable precision of less than 5% RSD (n = 10) was achieved. Total analysis time is less than 6 min. Linearity with a correlation coefficient of R2 = 0.9995 and a measured recovery of >99% under the specified conditions were achieved. Leveraging the additional back pressure generated by the modified jet assembly, a novel strategy of post-column backflushing with the detector fuel gas was successfully innovated to provide advantaged synergy in enhanced reliability and throughput of the analytical system. This backflushing approach had no known negative impact on conversion efficiency or performance of the jet assembly.The utility of this technique was demonstrated with relevant carbon dioxide applications in various sectors including carbonated beverage, environmental, and chemical industries.
2017
Spanjers, C., et al., Analytical Methods, “Increasing flame ionization detector (FID) sensitivity using post-column oxidation–methanation”
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The flame ionization detector (FID) is a robust tool in gas chromatography (GC) due to its sensitivity and linear response in the detection of common organic compounds. However, FID response to oxygenated or highly functionalized organic molecules is low, or in some cases non-existent, making it difficult or impossible to detect and quantify some organic compounds. In this work, the combination of a GC/FID system with a catalytic microreactor, which performs post-column combustion–methanation to convert organic compounds to methane, is shown to be an effective approach for quantifying low-response organic compounds. Molecules that were previously undetectable by conventional FID, including carbon monoxide and carbon dioxide, respond with the same high response of methane in the FID. Low-response molecules, including formaldehyde, formic acid, formamide, and ten other oxygenates also demonstrated enhanced detector response equivalent to that of methane in the FID. The linear response of the FID to these molecules and the equivalent sensitivity to methane indicate that accurate quantification is possible without the usual calibration-corrections (e.g., response factors or correction factors) to the FID response.
Prebihalo, S. E., et al. Analytical Chemistry, “Multidimensional Gas Chromatography: Advances in Instrumentation, Chemometrics and Applications”
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Scope of Review. Analysis of volatile and semi-volatile analytes by gas chromatography (GC) methods is an indispensable tool in the analytical chemist’s tool box. A myriad of fields of study rely upon the application of GC methods to address an ever growing demand to provide useful chemical information from GC data. As the realm of GC application has expanded, there has been an evolution to develop more powerful instrumental and data analysis approaches to keep pace with the wealth of complex samples that require analysis. To address this challenge, advances in GC instrumentation having evolved from one-dimensional gas chromatography (1D-GC) and heart cutting approaches such as (GC-GC), to instrumentation referred to broadly as multidimensional gas chromatography (MDGC), which can take on many forms. The principle form of MDGC that has gained wide implementation is comprehensive two-dimensional (2D) gas chromatography (GC × GC) as shown in Figure 1A, pioneered nearly 26 years ago by Liu and Phillips.1 When comparing 1D-GC (Figure 1B) relative to GC × GC (Figure 1C), the benefits of a secondary separation become evident. Blumberg and co-workers have theoretically determined that the 2D peak capacity provided by GC × GC compared to the peak capacity of 1D-GC is approximately an order of magnitude higher when the run times are held constant.2 This benefit is illustrated using a relatively complex sample of coffee. By adding a multivariate detector such as a time-of-flight mass spectrometry (TOFMS), another selective dimension of data is provided which may allow identification of analytes (Figure 1D). This review will focus essentially on GC × GC, with selected developments of other forms of MDGC also covered. In this regard, we focus primarily on research published since the last Fundamental Review published by Seeley and Seeley in 2013,3 with older publications covered as deemed necessary to provide additional insight into addressing the current challenges, and to put the more recent developments into historical context.
Abdelrahman, O., et al., Catalyst Science & Technology, “Simple Quantification of Zeolite Acid Site Density by Reactive Gas Chromatography”
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The Brønsted acid site densities of ZSM-5, BEA and single unit cell self-pillared pentasil (SPP) zeolites of varying Si/Al ratios were measured using a new technique, reactive gas chromatography (RGC), which utilizes alkylamine decomposition to selectively count Brønsted acid sites. Reactive gas chromatography condenses the conventional temperature-programmed desorption mass spectrometer (TPD-MS) setup into a single, fully-automated gas chromatograph (GC). Alkylamine decomposition reactions were conducted in a microcatalytic reactor placed within a temperature-controlled GC inlet liner. Products were then separated in a GC column and quantified with a flame ionization detector. A comparison between reactive gas chromatography measurements and conventional temperature programmed desorption methods showed agreement; RGC acid site density measurements were further confirmed by comparison with in situ pyridine titration of isopropanol dehydration. Reactive gas chromatography measurements performed using multiple alkylamines, were found to yield identical Brønsted acid site densities. The method of reactive gas chromatography was found to be highly sensitive, where siliceous materials with Brønsted acid site densities as low as ~1.0 μmol gcat-1 could be reliably measured.
Janis, G., et al., American Laboratory, “Quantitation Without Calibration: Eliminating the Requirement for Calibration Curves in the GC-FID Analysis of Ethanol in Blood, Urine, and Serum”
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While laboratories utilize many approaches to calibrate analytical assays, they always involve the analysis of one or more calibrators that have known levels of the analyte of interest. The response of the analyte of interest in test samples is directly or indirectly compared to the response of the same analyte in the calibrators to determine the concentration of the analyte in the test sample. Analyte calibration is burdened with limitations and potential bias: Calibrator preparation inherently contains a level of inaccuracy, which propagates to the quantitation of any unknown based on that calibration. Even small biases in the calibration will impact the quantitative accuracy of samples.
Beach, C., et al., AIChE Journal, “Complete Carbon Analysis of Sulfur-Containing Mixtures using Post-Column Reaction and Flame Ionization Detection”
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Quantitative analysis of complex mixtures containing hundreds-to-thousands of organic compounds rich in heteroatoms, including oxygen, sulfur, and nitrogen, is a major challenge in the fuel, food, and chemical industries. In this work, a two-stage (oxidation and methanation) catalytic process in a 3D-printed metal microreactor was evaluated for its capability to convert sulfur-containing organic compounds to methane. The microreactor was inserted into a gas chromatograph between the capillary column and flame ionization detector. Catalytic conversion of all sulfur-containing analytes to methane enabled carbon quantification without calibration, by the method identified as “quantitative carbon detection” or QCD. Quantification of tetrahydrothiophene, dimethyl sulfoxide, diethyl sulfide, and thiophene indicated complete conversion to methane at 450°C. Long-term performance of a commercial microreactor was evaluated for 2,000 consecutive injections of sulfur-containing organic analytes. The sulfur processing capacity of the microreactor was identified experimentally, after which reduced conversion to methane was observed.
Abdelrahman, O., et al., ACS Sustainable Chemistry & Engineering, “Biomass-Derived Butadiene by Dehydra-Decyclization of Tetrahydrofuran”
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Catalytic ring-opening dehydration of tetrahydrofuran (THF), itself a product of decarbonylation and reduction of biomass-derived furfural, yields 1,3-butadiene, an important monomer in rubbers and elastomers. It is demonstrated that dehydra-decyclization of THF with phosphorus-containing siliceous self-pillared pentasil (SPP) or MFI structure exhibits high selectivity to butadiene (85–99%) at both low (9%) and high (89%) conversion of THF. High selectivity to pentadiene and hexadiene was also obtained from 2-methyl-tetrahydrofuran and 2,5-dimethyl-tetrahydrofuran, respectively, with phosphorus-containing, all-silica zeolites.
Spanjers, C., et al., Analytical Methods, “Increasing Flame Ionization Detector (FID) Sensitivity Using Post-Column Oxidation-Methanation”
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The flame ionization detector (FID) is a robust tool in gas chromatography (GC) due to its sensitivity and linear response in the detection of common organic compounds. However, FID response to oxygenated or highly functionalized organic molecules is low, or in some cases non-existent, making it difficult or impossible to detect and quantify some organic compounds. In this work, the combination of a GC/FID system with a catalytic microreactor, which performs post-column combustion-methanation to convert organic compounds to methane, is shown to be an effective approach for quantifying low-response organic compounds. Molecules that were previously undetectable by conventional FID, including carbon monoxide and carbon dioxide, respond with the same high response of methane in the FID. Low-response molecules, including formaldehyde, formic acid, formamide, and ten other oxygenates also demonstrated enhanced detector response equivalent to that of methane in the FID. The linear response of the FID to these molecules and the equivalent sensitivity to methane indicate that accurate quantification is possible without the usual calibration-corrections (e.g., response factors or correction factors) to the FID response.
Abdelrahman, O., et al., ACS Catalysis, “Renewable Isoprene by Sequential Hydrogenation of Itaconic Acid and Dehydra-Decyclization of 3-Methyl-Tetrahydrofuran”
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Catalytic hydrogenation of itaconic acid (obtained from glucose fermentation) yields 3-methyl-tetrahydrofuran (3-MTHF), which then undergoes catalytic dehydra-decyclization to isoprene. It is demonstrated that a one-pot cascade reaction converts itaconic acid to 3-MTHF at ∼80% yield with Pd–Re/C catalyst and 1000 psig H2. Subsequent gas-phase catalytic ring opening and dehydration of 3-MTHF with phosphorus-containing zeolites including P-BEA, P-MFI, and P-SPP (self-pillared pentasil) exhibits 90% selectivity to dienes (70% isoprene, 20% pentadienes) at 20–25% conversion.
Supporting information, which includes experimental results and use of the Polyarc system
2016
Beach, C., et al., Analyst, “Quantitative carbon detector for enhanced detection of molecules in foods, pharmaceuticals, cosmetics, flavors, and fuels”
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Analysis of trace compounds, such as pesticides and other contaminants, within consumer products, fuels, and the environment requires quantification of increasingly complex mixtures of difficult-to-quantify compounds. Many compounds of interest are non-volatile and exhibit poor response in current gas chromatography and flame ionization systems. Here we show the reaction of trimethylsilylated chemical analytes to methane using a quantitative carbon detector (QCD; the Polyarc reactor) within a gas chromatograph (GC), thereby enabling enhanced detection (up to 10×) of highly functionalized compounds including carbohydrates, acids, drugs, flavorants, and pesticides. Analysis of a complex mixture of compounds shows that the GC-QCD method exhibitsfaster and more accurate analysis of complex mixtures commonly encountered in everyday products and the environment.
Spanjers, C. et al., American Laboratory:, “Calibration-Free Catalytic Microreactor for Analysis of Pesticides in Food”
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Professor Paul Dauenhauer and a team of researchers at the University of Minnesota wanted a faster and more accurate method to determine the concentrations of organic compounds, so they used a newly developed technology, the Polyarc reactor. The Polyarc reactor is a catalytic microreactor that converts organic compounds to methane at the exit of the GC and before detection in the FID. To optimize separation efficiency, the device has specially designed microchannels with catalysts to ensure full conversion of organic molecules to methane and a unique application of 3-D printing with stainless steel is used to create the reactor cartridge. Because FIDs are only sensitive to compounds containing carbon, the Polyarc reactor makes the response per carbon atom equivalent for all compounds. A detailed investigation of the device was recently published by the Catalysis Center for Energy Innovation (CCEI), and new applications for the reactor are being explored.
2014
Maduskar, S., et al., Lab on a Chip, “Quantitative carbon detector (QCD) for calibration-free, high-resolution characterization of complex mixtures”
