In-line Gas Chromatography Research Articles

Carbon Dioxide Reduction on Alloyed Galinstan

Solar powered electrochemical CO₂ reduction to disposable products is presently being developed as one of negative carbon emission technologies1. State-of-the-art electrocatalysts are mainly developed for the CO2 reduction to hydrogen rich products or chemical feedstock materials while for the above-mentioned application solid carbon-rich products are desired (best pure carbon). Even though the formation of solid products is sometimes observed on catalysts (coking effect), this usually leads to an undesirable irreversible deactivation of their solid interfaces.Thus, the development of next generation CO2 electrocatalysts is demanded based on liquid metal alloys such as galinstan (GaInSn). The advantage of using liquid phase electrodes is to eliminate coking and coarsening limitations that are associated with solid catalysts. For example, it has been reported that ceria-supported liquid galinstan can electrochemically produce carbonaceous materials from CO2 gas2. This shows, that doping with additional active elements can change the CO2 reduction activity of GaInSn in the direction of other desired products.Our work investigates the activity of galinstan for the electroreduction of CO2 depending on alloying with additional metals (such as Ce, Ag, Pb). While pure GaInSn shows a predominant activity for the formation of C1 products (CO, HCOOH) in DMF/H2O electrolyte, we are mainly interested in the formation of solid carbon or oxalate. Therefore, our investigations aim at finding suitable modifications of GaInSn that achieve high selectivity for these products. Electrochemical analysis coupled with in-line gas chromatography and in-line mass spectroscopy are used to characterize the reactivity. Furthermore, the influence of the water content of the organic electrolyte on the product selectivity will be investigated. In particular, to suppress the observed low hydrogen evolution as a by-product even more efficiently. May, M. M.; Rehfeld, K., Negative Emissions as the New Frontier of Photoelectrochemical CO2 Reduction. Advanced Energy Materials 2022, 2103801.Esrafilzadeh, D.; Zavabeti, A.; Jalili, R.; Atkin, P.; Choi, J.; Carey, B. J.; Brkljača, R.; O’Mullane, A. P.; Dickey, M. D.; Officer, D. L.; MacFarlane, D. R.; Daeneke, T.; Kalantar-Zadeh, K., Room Temperature CO2 Reduction to Solid Carbon Species on Liquid Metals Featuring Atomically Thin Ceria Interfaces. Nature Communications 2019, 10 (1), 865. Figure 1

Gas Crossover and Supersaturation in Advanced Alkaline Water Electrolysis

Conventional alkaline water electrolyzers operate with a finite-gap between the cathode and anode [1]. The ohmic resistance induced by this finite-gap results in energy losses. Therefore, the zero-gap assembly is considered an attractive configuration to perform advanced alkaline water electrolysis. However, gas crossover is enhanced in the zero-gap configuration by supersaturated hydrogen concentrations in the vicinity of the electrode. To avoid excessive gas crossover there is a limiting minimal operational current density.Different transport mechanisms can contribute to gas crossover through the porous separator, namely diffusion, convection, and electrolyte mixing. For well-balanced pressures and industrial flow rates, diffusion is the main contributor to gas crossover [2].Local supersaturation at the diaphragm interface significantly contributes to gas crossover [2]. To confirm this hypothesis, in-situ gas analysis experiments were conducted in an electrolysis setup equipped with in-line gas chromatography that could be operated with negligible influence of convective transport mechanisms to evaluate the diffusive transport in both zero- and finite-gap configurations.There is a clear distinction in gas crossover between zero- and finite-gap designs. In Figure 1 is shown that for the zero-gap assembly, hydrogen crossover rates were found to increase with current density, evidencing that supersaturation at the diaphragm interface plays an important role on gas crossover. In contrast, using a finite-gap configuration, gas crossover was significantly reduced and approached equilibrium diffusion rates, proving that gas crossover is mainly driven by diffusive hydrogen transport. Therefore, advanced alkaline electrolysis could be operated at higher current densities by applying a zero-gap configuration and reducing diaphragm thickness, but gas crossover leads to higher hydrogen in oxygen levels at low power load.[1] J. Brauns, T. Turek. “Alkaline water electrolysis powered by renewable energy: A review”. Processes, vol. 8, no. 2 (2020).[2] M. T. de Groot, J. Kraakman, R. Lira Garcia Barros. “Optimal operating parameters for advanced alkaline water electrolysis”. International Journal of Hydrogen Energy, vol. 47, no. 82 (2022) 34773-34783. Figure 1

Electrochemical Performance of Direct Ammonia Solid Oxide Fuel Cell

Recently, as regulations on greenhouse gas emissions have been strengthened in various industries such as automobiles and ships, many studies on alternative energy are being conducted. Hydrogen is a good energy carrier and an environmentally benign fuel because the reaction product is only water or water vapor when it is burned or is used for fuel cells. However, hydrogen suffer from its low specific volume, so the storage issue is still remained unsolved.Ammonia (NH3) has a higher energy density (12.7 MJ/L) than liquid hydrogen (8.5 MJ/L). Liquid hydrogen has to be stored at cryogenic conditions of –253°C, whereas ammonia can be stored at a much less energy-intensive –33°C. In addition, ammonia is much less flammable than hydrogen although it is hazardous to handle.In this study, anode-supported SOFCs consisting of LSCF-GDC cathode, YSZ electrolyte, and Ni/YSZ cermet anode was fabricated and their electrochemical performances (Impedance spectra, J-V curve and cell voltage degradation with operation time) were investigated at 600, 650, and 700°C under ammonia and hydrogen. Regardless of the operating temperature, the power densities of ammonia-fueled SOFCs were almost similar to those of hydrogen-fueled SOFCs. This suggested that the ammonia cracking reaction effectively occurred in the Ni-YSZ anode support. However, the cell voltage at 0.2 A/cm2 was slightly decreased as a function of operating time, which means that the nickel was degraded under ammonia atmosphere. The change of an anode’s microstructure before and after the degradation test will be discussed. In addition, Ni-YSZ catalysts for ammonia cracking were fabricated and their catalytic activity was measured in terms of operating temperature and space velocity using in-line gas chromatography. The phase evolution and microstructure of catalysts were characterized by XRD, SEM and TEM.

(Digital Presentation) Interfacial Durability of Anion Exchange Membrane Water Electrolyzers (AEMWEs)

There is a growing industrial appeal of anion exchange membrane water electrolyzers (AEMWEs) to produce hydrogen. This is spurred by the recent advancements in high current density operation capability with relatively low overvoltage performance. Cost reduction has been pursued by reducing the reliance on expensive platinum group metal (PGM) catalysts while still achieving long-term, continuous operation conditions most relevant to the industry: high current densities above 2 A/cm2 while retaining overvoltage performance so that overall cell potential is less than 2V.Along with a selection of appropriate PGM-free catalysts, other approaches exist that drive down the associated cost to produce hydrogen from water splitting. Sources of water are extended to brackish and even seawater to further drive down costs due to the removal of costly water purification requirements. The introduction of salt to the water source may improve overvoltage performance in an AEMWE by raising electrolyte conductivity, however, it may also lead to some unknown instability within more severe high current operating conditions. The challenge remains that AEMWE durability testing is not standardized, and more minute interfacial degradation mechanisms between ionomer, catalyst, membrane, and electrolyte are not well characterized for many industrially relevant materials. When approaching AEMWE performance improvements with PGM-free and variable electrolyte content in water solution sources, the long-term performance needs to be demonstrated in a stable and reliable manner.A series of in-situ Raman experiments are presented in coordination with ex-situ spectroscopic and physical analysis of components in PGM-free AEMWEs that are expected to contribute to overall degradation of electrolyzer performance. Interfacial durability improvements are sought by providing insight into the main sources of failure during high current and long-term operations. Electrochemical testing protocols are also developed and presented in order to seek standardization of testing procedures. In-line gas chromatography (GC) analysis is also presented in tandem with other analytical methods to confirm product gas purity and corroborate hypotheses on possible degradation mechanisms.

Evidence for the catalytic properties of ultramarine pigment

Abstract Ultramarine blue paint layers in oil paintings can be affected by ultramarine ‘disease’ or ‘sickness’: a phenomenon described by a grey appearance and a loss of detail in the artwork. An explanation for this phenomenon is an interaction between the organic binder network and ultramarine pigment, with the pigment acting as a catalyst for the breakdown of the network. This breakdown results in micro-cracks in the paint film, which influences the appearance of the artwork. To investigate the possible catalytic property of ultramarine pigment, a test reaction – the dehydration of methanol to dimethyl ether – was carried out, with and without ultramarine pigment present in a micro-reactor with in-line gas chromatography mass spectrometry. It was observed that a higher yield of dimethyl ether was obtained in the presence of ultramarine pigment, confirming that ultramarine pigment possesses catalytic properties similar to commercial zeolitic silica-alumina catalysts.

Tracking Gas Diffusion Electrode Flooding in CO2 Electrolyzers Via Electrochemical Double Layer Capacitance

As electrochemical technologies such as batteries, fuel cells, and water electrolyzers advance and transform the electric and transportation sectors, there is increasing interest around the role of electrochemistry in sustainable chemical manufacturing. As an example, blending electrochemically generated carbon monoxide (CO) and hydrogen, derived from carbon dioxide (CO2) and water electrolyses respectively, could constitute a renewable scheme to produce syngas for Fischer-Tropsch gas-to-liquids processes1. Decades of fundamental research into electrochemical CO2 reduction (CO2R) coupled with emerging engineering and economic incentives have shifted the field’s focus towards high-performance, gas-fed electrolyzers. Catalyst-coated gas diffusion electrodes facilitate such reactor configurations by providing physical separation between the gaseous reactants and the liquid electrolyte. While high geometric-area-specific electrochemical activity has been demonstrated with commercial gas diffusion electrode materials for a variety of both CO- and hydrocarbon-selective metal catalysts2,3, longevity remains a challenge and performance decay is often attributed to electrode deficiencies. To date, most gas diffusion layers reported in the CO2R literature have been repurposed from fuel cell applications, in which the transport of water to and from the catalyst layer is crucial to device operation. To this end, in fuel cells, densely-packed microporous layers serve both as catalyst-layer substrates and effective media for water management. However, the efficacy of this layer as a barrier to liquid electrolyte flooding in CO2R is limited by increasing hydrophilicity upon exposure to reducing potentials and high local pH. New operando diagnostic techniques are needed to probe the stability of the gas-liquid interface in gas-fed CO2 electrolyzers with flowing liquid electrolytes4. In this presentation, we propose a new experimental approach for determining the relationship between cell operating conditions and the eventual degradation of CO2-to-CO faradaic efficiency. Specifically, we propose combining periodic in-situ electrochemical-double-layer-capacitance-based electrolyte wetting predictors with in-line gas chromatography characterization of CO2R products. Voltammetric- or impedance-based methods are often used to estimate electrochemically active surface area of porous carbons in supercapacitor applications, but have yet to be used to probe electrolyte wetting in CO2R gas diffusion electrodes5. To demonstrate this technique, we evaluate the flooding tolerance of silver-coated gas diffusion electrodes under a range of operating conditions and using a number of commercial gas diffusion layers. Additionally, we discuss the impact of electrolyte properties (e.g., composition, pH), electrode properties (e.g., PTFE-content, macroporous layer, cracking), and operating conditions (e.g., pressure differential, current density, temperature) on flooding phenomena to identify key descriptors that can inform the design of more resilient electrode configurations. Funding Acknowledgement We gratefully acknowledge funding support from the US Department of Energy SBIR Program Grant # DE-SC0015173 and Royal Dutch Shell plc through the MIT Energy Initiative. References (1) Bushuyev, O. S.; De Luna, P.; Dinh, C. T.; Tao, L.; Saur, G.; van de Lagemaat, J.; Kelley, S. O.; Sargent, E. H. What Should We Make with CO2 and How Can We Make It? Joule 2018. https://doi.org/10.1016/j.joule.2017.09.003. (2) Ma, S.; Sadakiyo, M.; Luo, R.; Heima, M.; Yamauchi, M.; Kenis, P. J. A. One-Step Electrosynthesis of Ethylene and Ethanol from CO2 in an Alkaline Electrolyzer. J. Power Sources 2016, 301, 219–228. https://doi.org/10.1016/j.jpowsour.2015.09.124. (3) Verma, S.; Lu, X.; Ma, S.; Masel, R. I.; Kenis, P. J. A. The Effect of Electrolyte Composition on the Electroreduction of CO2 to CO on Ag Based Gas Diffusion Electrodes. Phys. Chem. Chem. Phys. 2016, 18 (10), 7075–7084. https://doi.org/10.1039/C5CP05665A. (4) Higgins, D. C.; Hahn, C.; Xiang, C.; Jaramillo, T. F.; Weber, A. Z. Gas-Diffusion Electrodes for Carbon-Dioxide Reduction: A New Paradigm. ACS Energy Lett. 2018. https://doi.org/10.1021/acsenergylett.8b02035. (5) Verbrugge, M. W.; Liu, P. Analytic Solutions and Experimental Data for Cyclic Voltammetry and Constant-Power Operation of Capacitors Consistent with HEV Applications. J. Electrochem. Soc. 2006, 153 (6), A1237–A1245. https://doi.org/10.1149/1.2194610.

The Electrochemical Properties of Nanocrystalline Gd0.1Ce0.9O1.95 Infiltrated Solid Oxide Co-Electrolysis Cells

Ni-YSZ/YSZ/GDC/LSCF6428-GDC10 solid oxide cells were fabricated and investigated in high-temperature H2O/CO2 co-electrolysis using various inlet fuel compositions at 800°C. Furthermore, to see the effect of infiltration on co-electrolysis, the precursor solution for a 10% gadolinium-doped ceria (GDC10) catalyst was dispersed into a fuel electrode backbone by a controlled urea/cation infiltration method. The influence of the inlet gas composition on the syngas product ratio was investigated by in-line gas chromatography. To understand the high-temperature H2O/CO2 co-electrolysis cell performance, electrochemical impedance spectroscopy (EIS) under open-circuit voltage and I-V characteristics, by the electrochemical reactions occurring at the electrodes of prepared solid oxide electrolysis cell (SOEC) were examined. When the inlet gas composition was N2 63.5%, H2 5%, CO2 11.5% and H2O 20% under electrolysis current density at −0.6 A cm−2, the H2/CO ratio of infiltrated cell was improved from 2.1 to 2.8 compared with the non-infiltrated cell. The thermodynamic factors determining the size, morphology and shape of the infiltrated particles were discussed.

Cu4sn/C As Electrocatalyst for Selective Electrochemical Reduction of CO2 to CO: Investigation V ia on-Line Mass Spectrometry and in-Line Gas Chromatograph

Different strategies for the global climate change and the carbon dioxide (CO2) emission reduction are being the goal of many researches in recent year. The application of new technologies for direct utilization of CO2 conversion could be interesting options to recycling the molecule. The electrochemical reduction for the conversion of CO2 into added-value carbon-based products as useful fuels has been studied and it involves a new source of sustainable energy. Among the different investigated electrocatalysts, Cu is distinctive for generating hydrocarbons, mainly methane (CH4) and ethylene (C2H4) [1,2], but suffer from deactivation and low faradaic efficiency (FE). Herein, it was investigated the behavior of carbon-supported Sn-modified copper alloy nanoparticles (Cu4Sn/C) for the carbon dioxide electroreduction, and the reaction products were monitored by on-line Differential Electrochemical Mass Spectrometry (DEMS) measurements. The faradaic and ionic currents for m/z = 2 (H2) and 28 (CO), obtained during DEMS experiments of cyclic voltammetry for Cu4Sn/C, in CO2-saturated 0.1 mol L- 1 KHCO3 electrolyte, at room temperature, showed that the CO/H2 ratio for Cu4Sn/C is lower than that for Au/C (included for comparison - known as an efficient electrocatalyst for CO generation), but higher when compared to that for Sn/C (which is known to produce CO and HCOO- ion in parallel to H2 [3]) and Cu/C (for copper, the m/z = 28 has contribution from methane and ethylene fragments). Stability tests, performed via chronoamperometric curves, showed that the CO signal for Au/C decreased within few minutes, with the concomitant increase of the H2 formation, evidencing deactivation during the CO2 electroreduction. This is probably due to accumulation of adsorbed CO-like intermediates [4]. On the other hand, and interesting, the CO signal for Cu4Sn/C alloy nanoparticles remained stable. Long-term stability test, however, are still necessary to address this important aspect. Quantitative analyses obtained by using in-line gas chromatography have shown FE for CO production of 23 and 13 % for Au/C and Cu4Sn/C, respectively. Therefore, the results obtained herein revealed that CO can be produced by using the non-noble metal-based Cu4Sn/C electrocatalyst. Although this material presented lower faradaic efficiency than that for Au/C, the electrochemical and DEMS measurements demonstrated higher stability for CO generation during the electrochemical polarization. Acknowledgements The authors thank FAPESP (2014/26699-3, 2013/16930-7 and 2016/13323-0) and CNPq for financial support.

Hydrogen production by methane decomposition over Co-Al mixed oxides derived from hydrotalcites: Effect of the catalyst activation with H2 or CH4

This study examines the influence of catalyst activation for methane decomposition over Co-Al mixed oxides derived from hydrotalcites. Samples were prepared by coprecipitation and characterized by surface area measurements and temperature-programmed reduction. Spent catalysts and carbon produced in the reaction were characterized by X-ray diffractometry, temperature-programmed oxidation and scanning electron microscopy. Activity runs using previously reduced samples with H2 or activated under CH4 flow were carried out in a fixed-bed reactor between 500 and 750 °C using in-line gas chromatography analysis. The specific surface area decreases as the Co/Al ratio increases, which is related to the increased Co3O4 phase rather than Co-Al mixed oxides. The TPR results indicate the reduction of four types of Co species: Co3+ and Co2+ species from Co3O4, and Co from inverse spinel (Co2AlO4) and normal spinel (CoAl2O4). Reduction with hydrogen at 750 °C was very severe. Samples reduced with H2 showed large Co° crystallites, which increased with the Co/Al ratio. Co-Al catalyst activation under methane flow leads to lower crystallite size and higher thermal stability for hydrogen production by methane decomposition.

Catalytic decomposition of methane over Ni/SiO2: influence of Cu addition

The influence of Cu addition to Ni/SiO2 catalysts was studied in the catalytic decomposition of methane. Samples were prepared by impregnation and characterized by SBET, TPR, TPO, XRD and Raman spectroscopy. The activity tests were performed at temperatures ranging from 500 to 700 °C in a fixed bed reactor with in-line gas chromatography analysis. The presence of copper had an effect on the SBET of calcined samples, improving the dispersion and decreasing the reduction temperature of NiO particles. The addition of small amounts of copper facilitates the activation of NiO with methane and allows obtaining small crystallites of Ni°, which prevents the catalyst deactivation by sintering in temperatures above 500 °C. The characterization of carbon deposited on Cu-containing samples indicated the formation of multi-walled carbon nanotubes. The sample containing 1 wt% of Cu has the best performance for the production of hydrogen from methane decomposition.

Kinetic and Molecular Modeling of Selected Bio-hazardous By-products from High Temperature Cooking of Goat Meat

The environmental fate of thermally released organic toxins including radical formation from high temperature cooking has received mounting global concern due to the potential health impacts associated with them. Therefore, this contribution investigates the thermal degradation kinetics of pyrolysis products of red meat under conditions representative of high temperature cooking. Evolution of selected molecular toxins was monitored using an in-line Gas Chromatography hyphenated to a mass spectrometer (GC-MS) in the temperature range 500–525°C. The primary focus is to propose a kinetic model for the thermal destruction of bio-hazardous byproducts; 2-(ethylthio)phenol, indole and 2, 3-dimethylhydroquinone within a temperature region 723 and 798 K using pseudo-first order rate law. A reaction time of 2.0 s was employed in line with the average residence time in combustion systems. Nonetheless, for the formation kinetics of 2-(ethylthio)phenol), various cooking times were chosen. Kinetic results showed that the destruction rate constants for indole, 2, 3-dimethylhydroquinone, and 2-(ethylthio)phenol at 798 K were 1.19, 1.42, and 1.35 s−1 respectively. GC-MS results revealed the amount of 2-(ethylthio)phenol evolved decreased with increase in the cooking time. The scission of the phenyl-sulphur linkage in 2-(ethylthio)phenol was determined using the density functional theory (DFT) and found to proceed with an energy barrier of 319.31 kJmol−1. The band-gap energy for 2-(ethylthio)phenol was calculated using Chemissian and found to be 5.298 eV. The kinetic behavior of combustion by-products from red meat is important in understanding the formation of environmentally toxic free radicals from high temperature cooking considered harmful to human health and natural ecosystems.

Hydrogen Production by Methane Decomposition Over Cu–Co–Al Mixed Oxides Activated Under Reaction Conditions

The decomposition of methane over Cu–Co–Al mixed oxides activated under the reaction conditions was studied. The samples were prepared by co-precipitation and characterized by SBET, TPR and XRD. The carbon produced in the reaction was characterized by XRD and TPO. Activity runs were performed in a fixed-bed reactor between 500 and 750 °C using in-line gas chromatography analysis. The results show a strong influence of copper on the structural and catalytic properties of Cu–Co–Al catalysts. The interaction between the Cu and Co dramatically decreases the reduction temperature of Co3O4 and CoAl2O4 and the activation can be performed with the methane feed. The activity at lower temperatures is attributed to Co3O4 phase. The higher the Cu amount, the more active the catalyst at lower temperatures and the lower the stability at higher temperatures. The phase CoAl2O4 is responsible by the surface area and by the thermal stability of these catalysts. Hydrogen production can be carried out over Cu–Co–Al catalysts containing small amounts of copper of approximately 3 %, activated under the reaction conditions and at temperatures below 600 °C.

Production Method for Methane Hydrate Sees Scientific Success

The testing flare burns brightly during a methane hydrate production test of the Ignik Sikumi No. 1 well on the Alaskan North Slope. A production method that could unlock large reserves of methane hydrate in sand-dominated reservoirs was tested successfully from a scientific and operational standpoint in a recent research experiment on the Alaskan North Slope (ANS). The experiment was conducted by the National Energy Technology Laboratory (NETL) of the United States Department of Energy (DOE) in partnership with ConocoPhillips and Japan Oil, Gas, and Metals National Corporation. A proof-of-concept test was conducted between 15 February and 10 April at the Ignik Sikumi No. 1 well in the Prudhoe Bay field operated by ConocoPhillips. The production technique featured the injection of carbon dioxide (CO2) to exchange and release methane (CH4) from the hydrate, a method developed through laboratory collaboration between the University of Bergen in Norway and ConocoPhillips. The released gas was then produced by means of reservoir depressurization. “The test objective was to perform injection and flow-back from a single well to validate that the CO2/CH4 exchange mechanism demonstrated in laboratory tests will occur in a reservoir of natural methane hydrates,” said Ray Boswell, technology manager for gas hydrates at the NETL. It was the first field-level trial of a production method involving the exchange of CO2 with the methane molecules contained in a methane hydrate structure. “The focus of the test, including the design of the well, was on the technical feasibility of this new technology, rather than an attempt to produce gas at commercial rates,” Boswell said. CO2 Mixture Injected in Reservoir The Ignik Sikumi well test was equipped with downhole fiber-optic distributed temperature and acoustic sensing, three downhole pressure gauges, and full surface instrumentation, including high-resolution in-line gas chromatography. Over a 13-day period, a carbon dioxide/nitrogen mixture was successfully injected into the 30-ft-thick reservoir interval, saturated with methane hydrate, without loss of injectivity. This was followed by a production stage in which the pressure was held above the stability pressure of the in-situ methane hydrate. CH4 was produced during this stage, and initial data analyses indicated that CO2 exchange was achieved. Ongoing analyses of the extensive datasets acquired at the field site are under way to determine the overall efficiency of simultaneous CO2 storage/CH4 production from the reservoir. As part of the demonstration, the depressurization phase of the test extended for 30 days. The longest previous field test of depressurization to extract gas from hydrate lasted 6 days as part of a Japanese-Canadian testing program at the Mallik well in Canada’s Northwest Territories during 2007 to 2008.

Hydrogen and boric acid production via boron hydrolysis

Abstract Hydrolysis of boron is investigated as a part of a boron/boron oxide solar water splitting-thermochemical cycle. Boron was hydrolyzed and boron oxide was gasified with steam in a tubular reactor. The effects of the reactor temperature and water flow rate on hydrogen production and boron oxide gasification were studied at different furnace set point temperatures and water flow rates. The produced hydrogen was measured by inline gas chromatography. Results show that the hydrogen production rate increased by increasing the reaction temperature and water flow rate. The range of hydrogen production efficiency of 95–100% was obtained for all experiments, as well as a full conversion of the boron particles to boron oxide, and the boron oxide to orthoboric acid. It was observed that the hydrogen production rate was high at the beginning of the hydrolysis process and decreased gradually with time. The X-ray analysis showed that the boron was converted into boron oxide and boric acid. The formation of a boric acid layer on the reactor walls was attributed to the gasification of the boron oxide.

Complementary Methods for the Determination of Dissolved Oxygen Content in Perfluorocarbon Emulsions and Other Solutions

Perfluorocarbons (PFCs) are compounds with increased oxygen solubility and effective diffusivity, making them ideal candidates for improving oxygen mass transfer in numerous biological applications. Historically, quantification of the mass transfer characteristics of these liquids has relied on the use of elaborate laboratory equipment and complicated methodologies, such as in-line gas chromatography coupled with temperature-controlled glass fritted diffusion cells. In this work, we present an alternative method for the determination of dissolved oxygen content in PFC emulsions and, by extrapolation, pure PFCs. We implemented a simple stirred oxygen consumption microchamber coupled with an enzymatic reaction for the quantitative determination of oxygen by optical density measurements. Chambers were also custom fitted with lifetime oxygen sensors to permit simultaneous measurement of internal chamber oxygen levels. Analyzing the consumption of oxygen during the enzymatic reaction via recorded oxygen depletion traces, we found a strong degree of correlation between the zero-order reaction rate and the total measured oxygen concentrations, relative to control solutions. The values obtained were in close agreement with published values in the literature, establishing the accuracy of this method. Overall, this method allows for easy, reliable, and reproducible measurements of oxygen content in aqueous solutions, including, but not limited to PFC emulsions.