O2 Concentration In Gas Phase Research Articles

A Lab Assembled Microcontroller-Based Sensor Module for Continuous Oxygen Measurement in Portable Hypoxia Chambers.

BackgroundHypoxia-based cell culture experiments are routine and essential components of in vitro cancer research. Most laboratories use low-cost portable modular chambers to achieve hypoxic conditions for cell cultures, where the sealed chambers are purged with a gas mixture of preset O2 concentration. Studies are conducted under the assumption that hypoxia remains unaltered throughout the 48 to 72 hour duration of such experiments. Since these chambers lack any sensor or detection system to monitor gas-phase O2, the cell-based data tend to be non-uniform due to the ad hoc nature of the experimental setup.MethodologyWith the availability of low-cost open-source microcontroller-based electronic project kits, it is now possible for researchers to program these with easy-to-use software, link them to sensors, and place them in basic scientific apparatus to monitor and record experimental parameters. We report here the design and construction of a small-footprint kit for continuous measurement and recording of O2 concentration in modular hypoxia chambers. The low-cost assembly (US$135) consists of an Arduino-based microcontroller, data-logging freeware, and a factory pre-calibrated miniature O2 sensor. A small, intuitive software program was written by the authors to control the data input and output. The basic nature of the kit will enable any student in biology with minimal experience in hobby-electronics to assemble the system and edit the program parameters to suit individual experimental conditions.Results/ConclusionsWe show the kit’s utility and stability of data output via a series of hypoxia experiments. The studies also demonstrated the critical need to monitor and adjust gas-phase O2 concentration during hypoxia-based experiments to prevent experimental errors or failure due to partial loss of hypoxia. Thus, incorporating the sensor-microcontroller module to a portable hypoxia chamber provides a researcher a capability that was previously available only to labs with access to sophisticated (and expensive) cell culture incubators.

Non-linear response of carbon dioxide and methane emissions to oxygen availability in a drained histosol

Organic-rich wetland soils in the histosol soil order represent the largest soil carbon (C) pool globally. Carbon accumulation in these ecosystems is largely due to oxygen (O2) limitation of decomposition. Increased O2 availability from wetland drainage and climate change may stimulate C decomposition overall and affect the balance of carbon dioxide (CO2) and methane (CH4) greenhouse gas release. Characterizing relationships, including non-linearity, between soil O2 and C gas emissions is therefore critical to predict the partitioning and rate of C release from histosols under greater O2 availability. We varied gas-phase O2 concentration from 0.03 to 20 % in incubations of a sapric histosol and measured resulting CO2 and CH4 emissions. Efflux of CO2 increased and CH4 emissions decreased at higher O2 concentrations, and rates were best described by log-linear model fits. The non-linear response of CO2 and CH4 emissions to O2 concentration indicates that moist, C rich histosols may be highly sensitive to increases in O2 availability, even below concentration thresholds typically classified as anoxic.

Kinetics of nascent soot oxidation by molecular oxygen in a flow reactor

Oxidation kinetics of soot is typically measured with well aged soot as substrates. Recent studies show that nascent soot can have structures and surface composition drastically different from mature, graphitized soot. In the present study, the kinetics of nascent soot oxidation by molecular oxygen was observed at temperatures of 950, 1000 and 1050K for molecular oxygen concentrations ranging from 1000 to 7800ppm at ambient pressure in a coupled burner-stabilized stagnation flame burner and laminar aerosol flow reactor. The reactant particles, 10–20nm in diameter, were freshly synthesized from premixed flames of ethylene, n-heptane, and toluene and introduced into the flow reactor continuously. The kinetics of particle oxidation was measured through electric mobility measurement of particle size distributions before and after oxidation. It was found that the specific oxidation rate is has a first-order dependency on gas-phase O2 concentration over the range of O2 concentration studied. The rate measured is an order of magnitude larger than that predicted by the classical Nagle Strickland-Constable (NSC) correlation. The result suggests that the surface of nascent soot is considerably more reactive towards oxidation than graphite or graphitized soot.

The Diavik Waste Rock Project: Design, construction, and instrumentation of field-scale experimental waste-rock piles

The physicochemical processes that affect acid mine drainage (AMD) in unsaturated waste rock piles and the capabilities of small-scale laboratory experiments to predict AMD from waste rock are not well understood. An integrated laboratory and field study to measure and compare low sulfide waste rock and drainage characteristics at various scales has been initiated. This paper describes the design, construction and instrumentation of three field-scale experimental waste rock piles (test piles), and six active zone lysimeters at the Diavik diamond mine in the Northwest Territories, Canada. The test piles are comprised of granitic and sulfide-bearing metasedimentary waste rock excavated during open pit mining operations. One test pile contains waste rock with a target S content of <0.04wt.% S; the second test pile contains waste rock with a target S content of >0.08wt.% S; and the third test pile contains the higher sulfide waste rock (>0.08wt.% S) and was re-sloped and capped with a low permeability till layer and a low sulfide waste rock cover. The first two test piles are approximately 15m high with bases of 50m by 60m, and the re-sloped test pile has a larger base of 80m by 125m. Instrumentation was selected to measure matrix flow, geochemistry of pore water and drainage, gas-phase O2 concentration, temperature evolution, microbiological populations, waste rock permeability to air, and thermal conductivity, as well as to resolve mass and flow balances. Instrument locations were selected to characterize coupled physicochemical processes at multiple scales and the evolution of those processes over time. Instruments were installed at a density such that the number of instruments that survived construction (40% to >80% by instrument type) was sufficient to allow adequate characterization of the physicochemical processes occurring at various scales in the test piles.

DeNOx reactions on Cu-zeolites: Decomposition of NO, N2O and SCR of NO by C3H8 and CH4 on Cu-ZSM-5 and Cu-AlTS-1 catalysts

Cu-ZSM-5 and Cu-AlTS-1 catalysts were prepared by solid state ion exchange and studied in DeNOx reactions. A NO3 type surface complex was found to be an active intermediate in the decomposition of NO and N2O. Copper was oxidized to Cu2+ in the decomposition reactions. Oscillations at full N2O conversion were observed in the gas phase O2 concentration, without any change in the N2 concentration. The oscillation was synchronized by gas phase NO formed from the NO3 complex. The same complex seems to be an active intermediate also in NO selective catalytic reduction (SCR) by methane, whereas carbonaceous deposits play a role in NO SCR by propane. TPD reveals that only 10–20% of the total copper in the zeolites participates in the catalytic cycles.

Control of acetic acid concentration by pH-stat continuous substrate feeding in heterotrophic culture phase of two-stage cultivation of Alcaligenes eutrophus for production of P(3HB) from CO2, H2, and O2 under non-explosive conditions.

A-two stage culture method of hydrogen-oxidizing bacterium, Alcaligenes eutrophus, is used to produce poly-D-3-hydroxybutyrate, P(3HB) from CO2, O2, and H2 without using a very high oxygen transfer rate while maintaining the O2 concentration in gas phase below 6.9 (v/v)% to prevent detonation of the gas mixture. The two-stage method consists of a heterotrophic culture using fructose as carbon source for exponential cell growth and an autotrophic culture for P(3HB) accumulation. We investigated the use of acetic acid as a cheaper carbon source than fructose for the heterotrophic culture in the two-stage method. However, the acetate concentration in the culture system must be maintained at 1.0 g. dm-3 since its inhibitory effect on the cell growth is very strong. Then, high cell density cultivation of A. eutrophus was investigated by pH-stat continuous feeding of acetic acid to control acetate concentration. As a result, acetate concentration was automatically maintained around 1.0 g. dm-3 by using a feed with a composition in CH3COOH/CH3COONH4/KH2PO4 molar ratio of 5:1:0.084. Cell concentration increased to 48.6 g. dm-3 after 21 h of cultivation. The cell mass grown in the fed-batch culture on acetic acid was useful for P(3HB) production from CO2 in the subsequent autotrophic culture stage. Copyright 1999 John Wiley & Sons, Inc.

Regulation of Electron Transport in Photosystems I and II in C3, C3-C4, and C4 Species of Panicum in Response to Changing Irradiance and O2 Levels.

Regulation of the quantum yields of linear electron transport and photosystem II photochemistry ([phi]II) with changing irradiance and gas-phase O2 concentration was studied in leaf tissue from Panicum bisulcatum (C3), Panicum milioides (C3-C4), and Panicum antidotale (C4) at 200 [mu]bars of CO2 and 25[deg]C using infrared gas analysis and chlorophyll fluorescence yield measurements. When the O2 level was increased from 14 to 213 mbars at high irradiance, [phi]II increased by as much as 115% in P. bisulcatum but by no more than 17% in P. antidotale. Under the same conditions [phi]II increased to an intermediate degree in P. milioides. Measurements of accumulation of the photooxidized form of the photosystem I reaction center (P700+) based on the light-dependent in vivo absorbance change at 830 nm indicate that the steady-state concentration of P700+ varied in an antiparallel manner with [phi]II when either the irradiance or O2 concentration was changed. Hence, O2-dependent changes in [phi]II were indicative of variations in linear photosynthetic electron transport. These experiments revealed, however, that a significant capacity was retained for in vivo regulation of the apparent quantum yield of photosystem I ([phi]I) independently of [phi]II+ Coordinate regulation of quantum yields of photosystems I and II (expressed as [phi]I:[phi]II in response to changing irradiance and O2 level differed markedly for the C3 and C4 species, and the response for the C3-C4 species most closely resembled that observed for the C4 species. The fraction of total linear electron transport supporting photorespiration at 213 mbars of O2 was negligible in the C4 species and was 13% lower in the C3-C4 species relative to the C3 species as calculated from fluorescence and gas-exchange determinations. At high photon-flux rates and high O2 concentration, the potential benefit to light use for net CO2 uptake arising from lower photorespiration in P. milioides was offset by a reduced capacity for total CO2- and O2-dependent noncyclic electron transport in this species compared with P. bisulcatum.

Partial reduction of a vanadia/silica-titania catalyst with ammonia + nitric oxide at 473 K studied by electrical conductance and ESR measurements

Partial reduction of vanadia supported on silica-titania by NH3 + NO has been studied by electrical conductance and ESR measurements. The relationship between electrical conductance and degree of reduction was determined by oxidative and reductive titrations of V(IV) and V(V) species leached from catalyst samples which had been reduced to different levels. In situ monitoring of the steady-state V(IV) ion concentration by electrical conductance during reduction with NH3 + NO in the concentration range 0-600 ppm for each reactant in a 2 vol % O2/Ar carrier gas was performed. In a large excess of NH3, the V(IV) ion concentration increased sharply with even small additions of NO. In a large excess of NO, the NH3 + NO mixture exhibited first an oxidizing character, and the V(IV) ion concentration increased when P(NH3) > 1/6P(NO). The reaction order with respect to the NO concentration, determined from both the NO conversion and the initial rate of catalyst reduction in excess NH3, was found to be less than unity. Determination of the stoichiometry of the reaction with respect to O2 indicated that the gas-phase O2 concentration required to balance the reducing character of NH3 + NO mixtures on the surface was significantly higher than predicted by the balanced equation describing the reaction. ESR measurements on the catalyst detected V(IV) ions as vanadyl groups having two different coordination spheres. Reduction of the catalyst with NH3 + NO caused an increase in the V(IV) signal and a decrease of the hyperfine structure. (Less)