Unknown Gas Research Articles

Calibrating a gas chromatograph to measure tritium using calorimetry

The availability of calibrated gas mixtures in a tritium plant is an important precondition for correct analysis of unknown gas samples because a quantitative analysis with a gas chromatograph (GC) requires frequent calibration checks. To calibrate a GC for tritium, certified gas mixtures with different tritium concentrations are necessary. These mixtures can be produced directly in a laboratory. In this case an independent method is needed to determine the tritium concentration in the mixture with high accuracy. Calorimetry is the method of choice because its accuracy is better than 1% and it is non-destructive method. Using the closed tritium loop of the Tritium Laboratory Karlsruhe (TLK), different mixtures containing tritium in the range 1–100% have been produced and measured with one of the in-house calorimeters. After that the GC of the CAPER facility at TLK has been calibrated several times with an uncertainty of a few percents.

Sensor array data profiling for gas identification

The paper presents a new method of qualitative identification of gas. It is based on a dynamic response of sensor array with the emphasis on the processing of discrete measurement data. The information needed for identification of test samples is obtained in course of profiling the data from calibration measurements. This operation consists of the following steps: classification of data sets, selection of representative data sets, parameterization of classifiers associated with representative data sets and determination of data records. In our work Discriminant Function Analysis was used for data classification. The information saved in data record describes: the sequential number of discrete measurement, combination of gas sensors in this measurement which are best for classification of calibration samples, and the parameters of associated classifier. They are identifiers of gas class. The procedure of data record determination itself is time consuming. However this operation will be performed only at the stage of the development of the measurement instrument and when its malfunction is diagnosed. The routine use of the instrument will be restricted to gas identification task, which only utilizes the results of profiling. The identification of unknown gas is performed on the base of data records and measurement data obtained for this gas. Data records guide the preparation of data sets, separately for each class of gases. These data sets are used as input of the discriminant functions which have parameter values also indicated by data records. It was shown in the present contribution, that the qualitative identification of nine test gas samples (vapors of ethanol, acetic acid and ethyl acetate in air) with our method was very accurate and fast.

An all-sky survey at 230 GHz by MLS on Aura

The Microwave Limb Sounder (MLS) instrument is a small satellite-borne radio telescope. Its purpose is to make limb-scanning measurements of atmospheric composition. One of the gases to which it is sensitive is carbon monoxide (CO), detected via the J = 2 → 1 rotational transition at 230 GHz. CO is present in molecular gas clouds in the Milky Way. Although it was not designed for the purpose, MLS can detect emissions from galactic CO, allowing a map of the 230 GHz radio sky to be constructed. We report the MLS measurements of galactic radio emission and discuss their effect on the atmospheric mission of MLS. The region of the Milky Way with emissions strong enough to significantly affect MLS observations of atmospheric CO is identified. Ground-based radio astronomers have been mapping the sky using CO emission for many years. However, the MLS data are the first such survey to be carried out from space. The MLS survey covers a larger area of the sky than any other 230 GHz survey, but no previously unknown gas clouds are observed.

Determination of gas phase triacetone triperoxide with aspiration ion mobility spectrometry and gas chromatography–mass spectrometry

Aspiration ion mobility spectrometry (IMS) has been used for the first time to screen 3,3,6,6,9,9-hexamethyl-1,2,4,5,7,8-hexaoxacyclononane explosive, the most commonly known as triacetone triperoxide (TATP). Gaseous TATP was generated from synthesized solid compound, sublimed and directed to a portable chemical detection system comprised of an aspiration-type IMS detector and six semiconductor sensors. Different unknown TATP gas phase concentrations were produced and corresponding IMS and semiconductor responses were measured. The experimental concentrations were determined by gas chromatography–mass spectrometry (GC–MS). The results evidenced that the monitored compound in the gas phase was TATP. In addition, the determined TATP concentrations and corresponding IMS intensities showed that the IMS response values were proportional to the measured TATP concentrations.

Low energy elastic electron scattering from polyatomic targets

New differential cross-section measurements for elastic electron scattering from ethylene (C2H4), three primary alcohols, methanol (CH3OH), ethanol (C2H5OH) and propanol (C3H7OH) are reported. The measurements are obtained using the relative flow method with a thin aperture as the collimating target gas source. The relative flow method is applied without the molecular diameters restriction imposed by the relative flow pressure condition on helium (the calibrating gas) and the unknown gases (the primary alcohols). The experimental data were taken at incident electron energies of 1eV, 2eV, 5eV, 10eV, 15eV, 20eV, 30eV, 50eV and 100eV, but only a brief survey of these results will be made here. The experimental results are compared to theoretical differential cross-sections are obtained by using the variational multi-channel Schwinger method. Initial comparisons between theory and experiment show that present theory is well-able to model low electron scattering from these polyatomic targets.

Low energy elastic scattering of electrons from H2 and N2

Accurate normalized differential cross-sections for elastic electron scattering from H2 and N2 are reported. These measurements are obtained using the relative flow method with helium as the standard (calibrating) gas, except that a thin aperture source of gas is used, which obviates the need to know the gas kinetic molecular diameters of either the calibration gas (He) or the unknown gas (H2 or N2) whose differential cross-sections need to be determined. Our present measurements are found to be in very good agreement with past differential elastic electron scattering measurements using the relative flow with tube collimating sources and independently vindicate the application of the conventional relative flow method for ‘hard-sphere’ gases. They also resolve some observed differences between the differential cross-sections in the low incident energy region. They also provide a good test of our relative flow method for two well-known targets.

Low-energy electron scattering from methanol and ethanol

Measured and calculated differential cross sections for elastic (rotationally unresolved) electron scattering from two primary alcohols, methanol (CH3OH) and ethanol (C2H5OH), are reported. The measurements are obtained using the relative flow method with helium as the standard gas and a thin aperture as the collimating target gas source. The relative flow method is applied without the restriction imposed by the relative flow pressure conditions on helium and the unknown gas. The experimental data were taken at incident electron energies of 1, 2, 5, 10, 15, 20, 30, 50, and 100 eV and for scattering angles of 5°–130°. There are no previous reports of experimental electron scattering differential cross sections for CH3OH and C2H5OH in the literature. The calculated differential cross sections are obtained using two different implementations of the Schwinger multichannel method, one that takes all electrons into account and is adapted for parallel computers, and another that uses pseudopotentials and considers only the valence electrons. Comparison between theory and experiment shows that theory is able to describe low-energy electron scattering from these polyatomic targets quite well.

A Novel Gas Sensor Based on Tunneling-Field-Ionization on Whisker-Covered Gold Nanowires

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Typical gas ionization sensors (GISs) work by fingerprinting the ionization breakdown voltages of the gases to be identified. In this work, we developed a GIS that operates by field-ionizing the unknown gas at exceptionally low voltages. The resultant field-ion current-voltage <formula formulatype="inline"> <tex>$(I-V)$</tex></formula> characteristic was then used to identify the gas. Freestanding gold nanowires (AuNW), terminated with nanoscale whisker-like features, were employed as field-amplifiers to reduce the field ionization threshold voltages. Synthesis of the AuNWs was carried out by the template-assisted technique accompanied by two alterations: 1) polystyrene (PS) microspheres were incorporated to reduce the compactness of the pores, thus prevent the nanostructures from collapse, and 2) the template was impregnated by <formula formulatype="inline"><tex>$\hbox{HAuCl}_{4}$</tex></formula> to form gold nanowhiskers during the electrochemical nucleation of AuNWs. The sensor was tested in three elemental gases: Ar, <formula formulatype="inline"><tex>$\hbox{N}_{2}$</tex> </formula> and He, in a pressure range of <formula formulatype="inline"><tex>$0.01≪P≪100$</tex> </formula> torr. Each gas demonstrated a distinctive <formula formulatype="inline"> <tex>$I-V$</tex></formula> curve, particularly in the field-limited regime. The threshold ionization voltages ranged from 1 to 10 V, almost three orders of magnitude lower than the voltages used in field-ion-microscopy. The low-voltage field ionization was attributed to the field-amplifying nanoscale whiskers on the AuNW tips, as well as the presence of residual amorphous alumina with semiconducting characteristics, due to incomplete removal of the porous anodized alumina (PAA) template. </para>

Low energy elastic electron scattering from ethylene

Normalized differential cross sections for elastic electron scattering from ethylene (C2H4) are reported. The measurements are obtained using a novel version of the relative flow method with helium as the standard gas. Here, the relative flow method is applied without any prior knowledge of the gas kinetic molecular diameters of either the standard gas whose differential cross sections for electron scattering are known or the unknown gas whose differential cross sections for electron scattering need to be determined. Removal of this restriction is made possible by using an aperture-collimating source of the target gas instead of a conventional tube source. Importantly, the present method is accurate and more rapid than past elastic electron scattering experiments using the relative flow method, which employed tube-collimating gas sources. Our present measurements are used to test the reliability of past measurements for ethylene and so to resolve a recent disagreement between theory and experiment concerning the elastic electron scattering differential cross-section data for ethylene at low energy, by providing experimental values independent of any systematic errors that might arise when estimating gas kinetic molecular diameters for large polyatomics. Our new arrangement also extends the relative flow method to be applicable to gases whose gas kinetic molecular diameters may not be available, such as gaseous biomolecules.

Signal processing of GC–MS data of complex environmental samples: Characterization of homologous series

Identification and characterization of homologous series by GC–MS analysis provide very relevant information on organic compounds in complex mixtures. A chemometric approach, based on the study of the autocovariance function, EACVF tot, is described as a suitable tool for extracting molecular–structural information from the GC signal, in particular for identifying the presence of homologous series and quantifying the number of their terms. A data pre-processing procedure is introduced to transform the time axis in order to display a strictly homogenous retention pattern: n-alkanes are used as external standard to stretch or shrink the original chromatogram in order to build up a linear GC retention scale. This addition can be regarded as a further step in the direction of a signal processing procedure for achieving a systematic characterization of complex mixture from experimental chromatograms. The EACVF tot was computed on the linearized chromatogram: if the sample presents terms of homologous series, the EACVF tot plot shows well-defined deterministic peaks at repeated constant interdistances. By comparison with standard references, the presence of such peaks is diagnostic for the presence of the ordered series, their position can be related to the chemical structure of the compounds, their height is the basis for estimating the number of terms in the series. The power of the procedure can be magnified by studying SIM chromatograms acquired at specific m/ z values characteristic of the compounds of interest: the EACVF tot on these selective signals makes it possible to confirm the results obtained from an unknown mixture and check their reliability. The procedure was validated on standard mixtures of known composition and applied to an unknown gas oil sample. In particular, the paper focuses on the study of two specific classes of compounds: n-alkanes and oxygen-containing compounds, since their identification provides information useful for characterizing the chemical composition of many samples of different origin. The robustness of the method was tested in experimental chromatograms obtained under unfavorable conditions: chromatograms acquired in non-optimal temperature program conditions and chromatographic data affected by signal noise.

Predictions of the adsorption equilibrium of methane/carbon dioxide binary gas on coals using Langmuir and ideal adsorbed solution theory under feed gas conditions

Abstract Presently many research projects focus on the adsorption and predictions of methane, nitrogen, carbon dioxide and their mixtures on coals under equilibrium gas conditions. It is highly important to develop a method for prediction of CO 2 /CH 4 adsorption on coal under feed (source) gas conditions in the fields of enhanced coal bed methane recovery and CO 2 sequestration in coal bed with CO 2 injection. The objective is to develop reliable models to predict the adsorption behavior of mixtures on coals under feed gas conditions. In this context, the adsorption and predictions of methane, carbon dioxide and three binary mixtures of these gases on two China coals under feed gas conditions have been performed on the experimental data and derived equation. Firstly, the experimental measurements of CH 4 , CO 2 and their binary gas adsorption isotherms to investigate the adsorption behavior and use for prediction of adsorption equilibrium were conducted at 301 K at pressures up to 10 MPa. Secondly, a calculation formula of adsorbed amount of total gas was derived from relation between adsorbed amount and feed gas composition at standard state on condition of unknown equilibrium gas concentration during adsorption. Thirdly, the extended Langmuir, ideal adsorbed solution (IAS) theory in conjunction with Langmuir were used to predict the experimental data of binary gas adsorption based on an iterative algorithm. Finally, the prediction accuracy for experimental data of total and adsorbed amount of component gas and free gas compositions were analyzed. Experimental data indicate adsorbed amounts of the total gas and single-component CO 2 increase, but adsorbed amounts of CH 4 increase at low equilibrium pressure and decrease at high pressure with increase of CO 2 concentration in feed gas. Model predictions based on single-component isotherms and the calculation formula show that the quantitative formula obtained can be used to predict adsorption equilibrium of CH 4 /CO 2 binary gas under feed gas conditions. The binary gas prediction data are quite variable and depend upon the feed gas composition. The IAS–Langmuir provides, on average, a better fit to total gas adsorption but is variable for the single-component adsorption with the feed gas composition. The predictions of total and component gas adsorption and equilibrium gas compositions illustrate similar trends with their experimental data.

High performance of a gas identification system using sensor array and temperature modulation

A sensor array based on metal oxide gas sensors has been used to identify three single industrial and environmental gases (carbon monoxide, acetylene and hydrogen sulphide). A temperature modulation method is applied to a sensor array and compared to experiments with different constant temperatures. The former shows more powerful ability in gas discrimination than the latter. Both principal component analysis (PCA) and artificial neural networks (ANN) are performed to classify and identify the target gases. The classification results show the potentiality of the system. Moreover, unknown gases are tested and they are well identified.

Amperometric sensor array for NO x, CO, O 2 and SO 2 detection

Using Nafion ®/Pt (or Au)/ceramic plate micro-electrodes prepared by microfabricating technologies as the sensing electrodes of a gas sensor array and BPN (backpropagation neural network) as the recognition algorithm, the sensing properties and optimal BPN structure for monitoring gas mixtures containing NO 2, NO, SO 2, CO and O 2 were studied. The limiting current potentials for anodic oxidation of NO on Au, SO 2 and CO on Pt, and cathodic reduction of NO 2 on Au and O 2 on Pt were found to be 0–0.5, −0.4 to 0.2, −0.4 to 0.1, 0.2–0.5 and 0.2–0.7 V (versus Pt), respectively. When the potentials were set at the values of mass-transfer control, the mass-transfer resistance in the gas diffusion layer could be neglected for gas flow rates greater than 300 ml min −1, and the individual sensitivities to NO 2, NO, SO 2, CO and O 2 were obtained to be 0.614, 0.445, 0.612, 0.557 and 0.433 nA ppm −1, respectively. Using the sensor array for monitoring gas mixtures, the optimal learning cycles, learning rate, input nodes, nodes in one hidden layer and output nodes of BPN based on 50 sets of learning data were obtained to be 1000, 0.01, 5, 7 and 5, respectively. The average predicting error for detecting an unknown gas mixture was found to be 8.61% based on the sensor array and optimal BPN.

Europa's atmosphere, gas tori, and magnetospheric implications

A two-dimensional kinetic model calculation for the water group species (H 2O, H 2, O 2, OH, O, H) in Europa's atmosphere is undertaken to determine its basic compositional structure, gas escape rates, and velocity distribution information to initialize neutral cloud model calculations for the most important gas tori. The dominant atmospheric species is O 2 at low altitudes and H 2 at higher altitudes with average day–night column densities of 4.5 × 10 14 and 7.7 × 10 13 cm −2 , respectively. H 2 forms the most important gas torus with an escape rate of ∼ 2 × 10 27 s −1 followed by O with an escape rate of ∼ 5 × 10 26 s −1 , created primarily as exothermic O products from O 2 dissociation by magnetospheric electrons. The circumplanetary distributions of H 2 and O are highly peaked about the satellite location and asymmetrically distributed near Europa's orbit about Jupiter, have substantial forward clouds extending radially inward to Io's orbit, and have spatially integrated cloud populations of 4.2 × 10 33 molecules for H 2 and 4.0 × 10 32 atoms for O that are larger than their corresponding populations in Europa's local atmosphere by a factor of ∼200 and ∼1000, respectively. The cloud population for H 2 is a factor of ∼3 times larger than that for the combined cloud population of Io's O and S neutral clouds and provides the dominant neutral population beyond the so-called ramp region at 7.4–7.8 R J in the plasma torus. The calculated brightness of Europa's O cloud on the sky plane is very dim at the sub-Rayleigh level. The H 2 and O tori provide a new source of europagenic molecular and atomic pickup ions for the thermal plasma and introduce a neutral barrier in which new plasma sinks are created for the cooler iogenic plasma as it is transported radially outward and in which new sinks are created to alter the population and pitch angle distribution of the energetic plasma as it is transported radially inward. The europagenic instantaneous pickup ion rates are peaked at Europa's orbit, dominate the iogenic pickup ion rates beyond the ramp region, and introduce new secondary plasma source peaks in the solution of the plasma transport problem. The H 2 torus is identified as the unknown Europa gas torus that creates both the observed loss of energetic H + ions at Europa's orbit and the corresponding measured ENA production rate for H.

低温工学に関わる真空の物理と技術 スーパーインシュレータ（ポリイミド及びポリエステル）のγ線照射後のガス生成量と機械的特性

Japanese intense spallation neutron source (JSNS) driven by 3 GeV protons with power of 1 MW is constructed under the joint project of Japan Atomic Energy Agency and High Energy Accelerator Research Organization. Supercritical hydrogen of around 20K with 2 MPa is selected as a neutron moderator material and cryogenic hydrogen transfer lines are constructed from the moderators to the refrigerator. Then, a super insulator (SI) is adopted to reduce heat load in the hydrogen transfer lines. We performed irradiation test of SI using 60Co gamma ray to evaluate the irradiation effect. Two kinds of super insulator (polyimide and polyester) coated both sides by aluminum with thickness of 5 x 10-8 m were irradiated. After gamma ray irradiation, tensile test and gas yield measurement of super insulator were performed. Polyester based SI became brittle at about 10 MGy, on the other hand, polyimide based SI did not loss ductility so much even 80 MGy. Polyester based SI generated gas yield higher than that of polyimide based SI about one order of magnitude. We developed the gas analysis method by using a Q-mass and a mass-flow, providing to identify the unknown gas (i.e. H2O) effectively compared to a gas chromatography method.

DETECTION OF INERT GASES BY COLD ELECTRON EMISSION FROM CARBON NANOTUBE EMITTERS

In this work, different from the typical gas sensors responding by gas adsorption on their surface, a new gas sensor using carbon nanotubes (CNTs) as electron emitters is introduced for detecting inert gases which hardly possess chemical or electrical adsorption in normal conditions. The proposed sensor works by figuring out the variation of the dark current and the initial breakdown voltage on Paschen's law under applied high voltage. As they depend on the gas composition and the pressure in a sealed chamber, it is possible to detect the identity and the concentration of unknown inert gas species.

CO in HiSelf‐absorbed Clouds in Perseus

We have observed 12CO J = 2 → 1 and J = 1 → 0 and 13CO J = 1 → 0 emission in two regions of H I self-absorption (HISA) in Perseus: a small, isolated HISA feature called the and a more extended HISA cloud called the complex. Using both large velocity gradient and Monte Carlo radiative transfer codes, we found that in the globule N(12CO) < 6.0 × 1015 cm-2, which, using photodissociation region (PDR) models, implies that N(H2) < 9.9 × 1020 cm-2. In the complex we found that the H2 column densities were in the range (1.2-2.2) × 1021 cm-2. By comparing the HISA and CO observations we were able to constrain the physical conditions and atomic gas fraction (f). In the globule, 8 K < Tspin < 22 K and 0.02 < f < 0.2, depending on whether the (unknown) gas density was 102, 103, or 104 cm-3. In the complex, 12 K < Tspin < 24 K and 0.02 < f < 0.05, and we were also able to constrain the gas density (100 cm-3 < n < 1200 cm-3). These results imply that the gas in the HISA clouds is colder and denser than that usually associated with the atomic ISM and, indeed, is similar to that seen in molecular clouds. The small atomic gas fractions also imply that there is a significant molecular component in these HISA clouds, even when little or no 12CO is detected. The level of 12CO detected and the visual extinction due to dust is consistent with the idea that these HISA clouds are undergoing a transition from the atomic to molecular phase.

Ethyl Pyruvate—A New Indicator of Flavor Stability of Beer and its Controlling Factors

Aldehydes and ketones play an important role in the flavor stability of beer. We have measured carbonyl compounds such as Strecker aldehydes to investigate the flavor stability of beer. It was found that an unknown gas chromatography(GC)/electron capture detector peak (peak X) of carbonyl compounds after derivatization with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine was correlated with sensory evaluations of beer. The peak was determined as ethyl pyruvate (EP) by using GC/mass spectrometry. EP formation was accelerated by decreasing the pH. The formation occurred even at the low temperature (2°C) at which secondary fermentation occurs. EP increased with increasing pyruvate and ethanol during primary fermentation and then decreased with decreasing pyruvate during secondary fermentation. The decrease in EP during secondary fermentation was affected by pyruvate. The amount of pyruvate decrease during secondary fermentation had a positive correlation with the number of yeast cells at the end of primary fermentation. That is, EP is an indicator affected by pH and the number of yeast cells during secondary fermentation, which are important factors for flavor stability. We think EP is an excellent index of flavor stability that can be used to optimize the fermentation conditions, e.g., selection of yeast strains, aeration, and the Drauflassen conditions.

Gas diagnosis by a quantitative assessment of the transient response of a capillary-attached gas sensor

A numerical comparison of the transient response of a capillary-attached gas sensor (CGS) to an unknown target gas (TG) with those previously recorded for reference gases, afforded TG identification. A CGS was fabricated by hermetic attachment of an 80 mm long glass tube of 2 mm internal diameter to a zinc oxide based resistive gas sensor. The normalized transient responses of the fabricated device to hydrogen, methanol, ethanol and butanol were recorded as references. The response to an unknown TG was then compared with the reference profiles after normalization. The means of comparison was the calculation of the square error integrals of the recorded response with respect to the reference profiles. The TG was identified by selection of the reference gas corresponding to the least square error integral calculated. The device could identify an unknown contamination among the references available. The method was proved to be applicable to a wide concentration range. Numerical examples, based on the actual test results, are presented.

Discrimination and identification of a refrigerant gas in a humidity controlled atmosphere containing or not carbon dioxide: application to the electronic nose

Atmospheric pollution and green house effects are now one of the major preoccupations to improve the general quality of life. With an electronic nose application we propose a system dedicated to the main detection of refrigerant Forane 134a (R134a) gas leakage in air conditioned systems and atmospheres. For our application based on a metal oxide type gas sensor array (six TGS elements) mainly coupled with discriminant factorial analysis (DFA) for the pattern recognition, we propose to study the effect of the relative humidity and an antagonist gas carbon dioxide as interfering gases on the R134a gas and concentration discrimination. We show that the relative humidity in a wide range (18–85%) has a more important influence on the target gas and concentrations discrimination than carbon dioxide. We present the discrimination results for the gases and afterwards for the R134a concentrations. Then we show the ability of our system to identify correctly a test data set composed of unknown gas samples. For the gases concentrations identification we also show that a correct identification rate can be obtained specially when the relative humidity rate range is reduced.