Standard Gas Mixtures Research Articles

Gas chromatograph calibration of gas mixtures using a versatile precision volumetric apparatus

A compact, volumetric apparatus was developed for accurate automated preparation of standard gas and gas-liquid mixtures for gas chromatograph detector calibration, with accuracies comparable to those from gravimetric or Coriolis flow methods. The method developed by the principal author is not an adaptation or extension of any other apparatus or technology, and measurements involve only stepper motor steps, temperature, and pressure ratios. Mixture preparation is accomplished via the displacement of gas between chambers in a highly uniform cylinder, separated by a movable piston. Piston movement, with piston end rods of exactly equal diameter, ensures that there is no change in interior volume, and the volume of gas displaced from the bottom into the top compartment is exactly proportional to the piston travel measured to within 10μm. The apparatus, operation, and previously unpublished measurements on common refinery gas mixtures over large concentration ranges are described in detail. These confirmed the accuracy and versatility of the apparatus and also the principle of no pressure change during mixture preparation, from sensitive pressure measurements. Conservative expanded uncertainties in prepared mixture mole fraction ranged from 0.001 to 0.002 over extended composition ranges. Absolute average deviations for the detector response factor for the mixtures ranged from 0.001 to 0.002. An exact new mathematical solution procedure permits the use of impure "pure" gases without loss of accuracy and can be applied to other procedures for standard gas mixture preparation. An exact expression is listed for determining "pure" gas purity.

Multicomponent Alkane IR Measurement System Based on Dynamic Adaptive Moving Window PLS

Infrared (IR) spectroscopy for multicomponent alkane measurement has shown excellent potentials in unconventional oil and gas exploration. However, the cross-sensitivity of alkane IR absorption and the complexity of unconventional oil and gas components place extreme demands on quantitative IR spectroscopy models. To cope with these problems, an adaptive moving partial least square (AMW-PLS) modeling method for the quantitative analysis of IR spectra is proposed in this paper. Based on the designed moving control function and dual endpoint independent moving strategy, AMW-PLS can quickly determine the optimal local modeling interval location and width by tracking the accuracy of the calibration model dynamically. By transposing the proposed AMW-PLS into the designed infrared gas logging system in this paper, 88 samples of 2 different mixture types were tested and compared with the other three typical analytical methods. The experimental results show that AMW-PLS can dynamically track the IR characteristic shifts caused by the changes in the gas mixture component complexity and concentration distribution, and thus achieves the best performance. The instrument achieved an average relative error of 3.3651% for five alkane substances in three standard industrial gas mixtures under strong interference, which provides new technical support for early discovery of oil and gas reservoirs.

A cheap handheld NIR spectrometric system for automatic determination of methane, ethane, and propane in natural gas and biogas

In this study, a new NIR detection system using a cheap handheld NIR spectrometer, and a tungsten lamp coupled to a lab-made NIR flow cell was developed for the successful automatic quantification of methane, ethane, and propane in natural gas and biogas samples. To prepare standard gaseous mixtures for full-spectrum PLS multivariate calibration modeling and to record the NIR spectra of these mixtures and samples, this NIR detection system was connected to a flow automatic system and a gas chromatograph. The raw and second-derivative NIR spectra of the calibration set were then employed to construct PLS models using full cross-validation leave-one-out. All models presented high correlation coefficients (>0.9) and root mean square error (<5% mol mol−1) values. However, the RMSEP values using raw and preprocessed datasets were statistically similar according to the F-test at the 95% confidence level. The advantage of using raw data is the elimination of the preprocessing step for future prediction of samples to be analyzed. Once the NIR detection system has been previously calibrated via an automatic or batch process, it can be used to monitor light hydrocarbons or other gases inline (as in pipelines).

Numerical qualification of eco-friendly gas mixtures for avalanche-mode operation of resistive plate chambers in INO-ICAL

Proposition and qualification of an eco-friendly gas mixture of Ar(5%):CO2(60%): N2(35%) for operating Resistive Plate Chambers of INO-ICAL experiment in avalanche mode is the soul of this work. The detector efficiency and streamer probability for the proposed mixture have been simulated using a hydrodynamic model developed by us. Efficacy of the mixture has been studied by comparing the simulated results to available experimental data for the standard gas mixture of R134a(95.2%):i-C4H10(4.5%):SF6(0.3%) to be used in INO-ICAL, as well as the same observables measured for other eco-friendly hydrofluoroolefin (HFO1234ze)-based potential replacements. To reduce the streamer probability of the proposed argon-based gas mixture at higher voltages, the usual practice of adding a small amount of electronegative gas SF6 has been tested. An alternative approach of lowering electronic threshold has been investigated as well for the same purpose.

Experimental Validation of a Novel Generator of Gas Mixtures Based on Axial Gas Pulses Coupled to a Micromixer.

In this work, a novel generator of gas mixtures previously numerically investigated and based on axial gas pulses coupled to a micromixer has been conceived, manufactured, and validated. Standard gaseous pollutant mixtures and pure nitrogen or pure air were introduced in a microdevice designed to generate alternating axial gas pulses which were downstream homogenized by means of a multi-stage modular micromixer. The dilution, and therefore the final pollutant concentration, was controlled by two parameters: the ratio between the times of each of the two gas pulses and the partial pressure of the pollutant(s) mixture added to the device. The gas mixture generator was coupled to an analyzer to monitor the concentration of aromatic pollutants. The response time was optimized to be lower than 2 min in accordance with the analytical instrument. The quantity of pollutants measured at the micromixer’s outlet increased linearly with the expected gas concentration of 3.7–100 ppb generated by this novel microfluidic generator and fitted perfectly with those obtained by a reference gas dilution bench. At 5 ppb, the precision on the concentration generated is close to that obtained with the conventional gas mixing bench, i.e., around 10%.

CVD synthesis of multi-layered polycrystalline diamond films with reduced roughness using time-limited injections of N2 gas

Multi-layered polycrystalline diamond (PCD) films were synthesized using microwave plasma-assisted chemical vapor deposition (CVD) with periodical addition (injections) of N2 gas to the standard CH4-H2 gas mixture. The aim of such an approach was to reduce the roughness of the films while preserving the overall high quality and phase purity of the PCD material. The thicknesses of the films were in the range of 5 to 51 μm, while the number of layers was from 1 to 15. The introduction of even the smallest amount of nitrogen leads to a significant (more than 2-fold) increase in the growth rate of PCD films. Optimized injection regimes allowed the reduction of the relative roughness (Sq/thickness) of the PCD films by more than 3 times in comparison with standard microcrystalline diamond film grown under similar conditions without N2 addition. The proposed method of periodic injection of N2 during growth restricted the formation of continuous NCD layers, which improved the overall sp3/sp2 ratio in comparison with standard multi-layered MCD/NCD materials. The obtained multi-layered PCD materials with reduced roughness may be used for the formation of protective and hard covers, optical coatings, electrochemical and thermal management applications. Prime novelty statementThe multi-layered PCD films were synthesized in a microwave plasma CVD in regimes with short-term periodic N2 injections in CH4-H2 process gas; the average growth rate is doubled owing to the pulsed nitrogen injection, while the surface roughness is reduced by more than 3 times in comparison with a standard (no N2 injection) microcrystalline film.

Speed of sound data, derived perfect-gas heat capacities, and acoustic virial coefficients of a calibration standard natural gas mixture and a low-calorific H2-enriched mixture

This work aims to address the technical aspects related to the thermodynamic characterization of natural gas mixtures blended with hydrogen for the introduction of alternative energy sources within the Power-to-Gas framework. For that purpose, new experimental speed of sound data are presented in the pressure range between (0.1 up to 13) MPa and at temperatures of (260, 273.16, 300, 325, and 350) K for two mixtures qualified as primary calibration standards: a 11 component synthetic natural gas mixture (11 M), and another low-calorific H2-enriched natural gas mixture with a nominal molar percentage xH2=3%. Measurements have been gathered using a spherical acoustic resonator with an experimental expanded (k = 2) uncertainty better than 200 parts in 106 (0.02%) in the speed of sound. The heat capacity ratio as perfect-gas γpg, the molar heat capacity as perfect-gas Cp,mpg, and the second βa and third γa acoustic virial coefficients are derived from the speed of sound values. All the results are compared with the reference mixture models for natural gas-like mixtures, the AGA8-DC92 EoS and the GERG-2008 EoS, with special attention to the impact of hydrogen on those properties. Data are found to be mostly consistent within the model uncertainty in the 11 M synthetic mixture as expected, but for the hydrogen-enriched mixture in the limit of the model uncertainty at the highest measuring pressures.

Effect of acute isooxic hypercapnia on oxidative activity of systemic neutrophils in endotoxemic rabbits.

IntroductionWhether carbon dioxide (CO2) affects systemic oxidative phenomena under conditions of endotoxemia is not sufficiently clarified. The study aimed to assess the impact of moderate acute hypercapnia on the respiratory burst of circulating neutrophils in mechanically ventilated endotoxemic rabbits.Material and methodsTwenty-four endotoxemic rabbits were mechanically ventilated with standard or CO2-enriched gas mixture in order to obtain isooxic hypercapnia. At a baseline point and following 180 min of hypercapnic ventilation, luminol-dependent chemiluminescence (CL) of circulating neutrophils and serum 2-thiobarbituric acid reactive substance (TBARS) concentrations were measured. Throughout the study, leukocyte and neutrophil counts, pH status, circulatory parameters and body temperature were also assessed.ResultsFollowing 180 min of hypercapnic ventilation, opsonized zymosan (OZ)-stimulated neutrophils showed lower CL vs. the control group (p = 0.004). Other parameters studied were not affected.ConclusionsShort-term isooxic hypercapnia in endotoxemic rabbits preserves circulating neutrophil count pattern and reactive oxygen species (ROS) generation, but it may reduce phagocytosis.

Determination of peppermint compounds in breath by needle trap micro-extraction coupled with gas chromatography–tandem mass spectrometry

Breath analysis is an alternative approach for disease diagnosis and for monitoring therapy. The lack of standardized procedures for collecting and analysing breath samples currently limits its use in clinical practice. In order to overcome this limitation, the ‘Peppermint Consortium’ was established within the breath community to carry out breath wash-out experiments and define reference values for a panel of compounds contained in the peppermint oil capsule. Here, we present a needle trap micro-extraction technique coupled with gas chromatography and tandem mass spectrometry for a rapid and accurate determination of alpha-pinene, beta-pinene, limonene, eucalyptol, menthofuran, menthone, menthol and menthyl acetate in mixed breath samples. Detection limits between 1 and 20 pptv were observed when 25 ml of a humidified standard gas mixture were loaded into a needle trap device at a flow rate of 10 ml min−1. Inter- and intra-day precisions were lower than 15%, thus confirming the reliability of the assay. Our procedure was used to analyse breath samples taken from a nominally healthy volunteer who was invited to swallow a 200 mg capsule of peppermint oil. Six samples were collected at various times within 6 h of ingestion. Analyte concentrations were not affected by the sampling mode (i.e. mixed vs. end-tidal fraction), whereas respiratory rate and exhalation flow rate values slightly influenced the concentration of the target compounds in breath samples.

Development of 100 μmol mol−1 Cl2 Standard Gas Mixture for Accurate Calibration of Ambient Cl2 Sensors and Stack Emission Monitors

To accurately measure Cl2 mixing ratio using stack emission monitors and leak monitoring sensors in a workplace, it is essential calibrating monitors and sensors periodically using a Cl2 standard gas mixture. Because there is no reliable analytical technique for Cl2, an international standard for high-pressure Cl2 gas mixtures has not been established. A novel approach for the quantification of Cl2 was developed using quadrupole mass spectrometry (QMS) with an expanded uncertainty of 0.7 μmol mol−1. A 100 μmol mol−1 chlorine (Cl2)/N2 gas mixture was produced through a two-step procedure involving dilution of Cl2 with N2 in high-pressure aluminum cylinders. To check the consistency between 100 μmol mol−1 Cl2 gas mixtures in different cylinders, Cl2 gas mixtures were quantified using the QMS based approach. It was found that four cylinders of 100 μmol mol−1 Cl2 gas mixtures prepared in 2016 agreed within 0.7 μmol mol−1. The long-term stability of 100 μmol mol−1 Cl2 gas mixtures was assessed through changes in the Cl2 mixing ratio over a one-year. It was found that the 100 μmol mol−1 Cl2 gas mixture was stable within ±0.7 μmol mol−1 over one year. Finally, 100 μmol mol−1 Cl2/N2 gas mixture was successfully developed in a high pressure cylinder with an expanded uncertainty of 2.0 μmol mol−1 (k = 2; 95% confidence level).

Investigation of the Dynamism of Nanosized SOA Particle Formation in Indoor Air by a Scanning Mobility Particle Sizer and Proton-Transfer-Reaction Mass Spectrometry

Terpenes are VOCs of particular importance, since they are emitted from a wide range of indoor sources and are considered to be precursors of Secondary Organic Aerosol (SOA) formation. It has been proven that SOA particles, especially nanosized ones, pose a threat to human health. In this research, experiments with the application of an environmental chamber and real-time measurement techniques were carried out to investigate in a complimentary way the formation of monoterpene oxidation products and nanosized SOA particles initiated by monoterpene ozonolysis. Proton-Transfer-Reaction Mass Spectrometry with a Time-Of-Flight analyzer (PTR-TOF-MS) and a Scanning Mobility Particle Sizer (SMPS) were applied to determine in real time the dynamism of the formation of the corresponding terpene ozonolysis products and submicron SOA particles. Results proved that firstly, oxidation products were formed, and then, they underwent nucleation and condensation, forming particles whose diameters grew with time. The oxidation products formed were different depending on the type of terpenes applied. The comparison of the results obtained during the experiments with gaseous standard mixtures and real samples commonly present and used in indoor air revealed that the diversified chemical composition of the emission source had implications for both the particle formation initiated by the oxidation of essential oil components and the chemical reactions occurring via the oxidation process. With the instrumentation utilized, the concentration changes at the level of a few ppbv could be monitored.

Study of Polyoxometalates Based Films Formation with High Gas Sensitivity

Introduction Inorganic oxide films activated with different additives are the unique sensitive layers for working at room temperature sensors. The sensor behavior of nanostructured activated silica films produced by sol-gel route was examined for environment control. Polyoxometalates (POMs) of Dawson type were used as additives in the silica matrix for gas sensitivity. POMs have good electronic conductivity and chemical stability. These compounds can act as reversible reagents in the reactions of ligand exchange and redox transformations, accompanied by changes in current carrier concentration or catalyze of such transformations that can be used in chemical sensors. Their redox properties can be varied within broad limits due to changing the heteropolyanion composition [1-4]. Porous silica is a unique matrix for chemical sensors, which has a lot of excellent physical and chemical properties [5]. Method The sensor’s interdigital structure was made by microelectronic planar technology as shown in figure 1. The active area of the sensor was 4 x 4 mm. The thickness of the electrodes was 0,2 mm. The width of finger pairs of electrodes and distance between them were 20 μm. The method of hydrolythic polycondensation from tetraethyl orthosilicate solutions was used for forming complex silica films in this work. Films were deposited by a centrifugation from solutions based on tetraethyl orthosilicate and polyoxometalate. POMs with various compositions have been incorporated into the initial solution. The developed technology of multistep temperature treatment up to 413 K allowed film properties stabilizing.The conditions of film formation varied during the tests: solution composition, temperature, and application modes. Morphology and infrared spectra of the layers were studied using Solver-P47 scanning probe microscope (NT-MDT, Russia) and spectrometer Bruker EQUINOX 55 (Germany). Standard gas mixtures (MGPZ, Russia) and Environics – 4000 gas-mixture generator (Environics, USA) were used to measure the properties of sensors. Electrical parameters of the sensors have been measured in real-time mode. Environment influence on sol preparation and films forming was investigated. Results and Conclusions Films had thickness of 200-300 nm and nanoscale pores. The metrological parameters of sensors depend mainly on different parameters: synthesis conditions and chemical content of sensitive film, temperature of the environment, annealing temperature, storage conditions and duration after heat treatment. Temperature treatment and decreasing of environment humidity lead to acceleration of hydrolythic polycondensation of solutions and stabilization of sensitive films at right conditions as demonstrated in figure 2. Introduction of heteropolyanion into film resulted in film’s mass stabilization. The temperature treatment don’t disturb POM molecule in the film. The polyoxometalates didn’t display their catalytic activity at weight content less than 10 % in the film. The increase in conductivity is observed due to an increase in the concentration of charge carriers on the surface of the film, donors of which are introduced into the film POM molecules. And gas sensitivity maximum decreases at weight content more than 50-60 % in matrix what is explained apparently by the formation of crystalline aggregates POM in the volume of the film. Besides the humidity adsorption on the film’s surface contribute to the sensor response. Adding of Mn3P2Mo18O62 into silica film resulted in high sensitivity to ethanolamine (up to 10 times) more than to ammonia as shown in figure 3. Obviously, this is explained by the reaction of ethanolamine complexation with Mn ions, among the possible valence states of which the strongest complex with ethanolamine molecules is formed by Mn3+. An equilibrium shift towards Mn3+ and a decrease in the redox potential of the Mn3+/Mn2+ pair leads to an intramolecular reduction reaction of the heteropolyanion. This interaction is quick (less than 30 s) and reversible at room temperature.

The effects of carbon incorporation on the refractive index of PECVD silicon oxide layers

Silicon oxide (SiOx) has many applications, including as a low-refractive index material. Plasma enhanced chemical vapor deposition (PECVD) processes are facile, low temperature routes to produce thin SiOx layers. A route to decrease the refractive index of SiOx films is to increase the layer porosity although maintaining structural and optical stability remains challenging. Organic carbon-containing sacrificial layers have been shown to modify the growth and resulting structure of PECVD SiOx layers. In this work, we study the effect of adding methane (CH4) to the standard SiOx process gas mixture (silane and nitrous oxide) and varying deposition temperatures and microwave power in an industrial-scale, microwave PECVD reactor. Spectral ellipsometry was used to measure the optical properties of deposited layers, Fourier-transformed infrared (FTIR) spectroscopy to determine bonding and the layer porosity, and optical emission spectroscopy to characterize the plasma. We propose two regimes characterized by whether adding CH4 increases or decreases the refractive index and porosity of deposited layers compared to SiOx layers grown under standard conditions. However, the magnitude of the effect of adding CH4 was not large and would not find industrial application. Furthermore, the deposited layers’ refractive indices increased over time, indicating that the effects of adding CH4 to the process gas mixture were not stable. To help explain our results and to provide guidance for future efforts to better control the refractive index of PECVD SiOx layers via carbon incorporation while maintaining layer stability, we propose possible growth pathways for our layers considering both plasma reactions and surface processes.

Final report of supplementary comparison for APMP.QM-S7.1: methane in nitrogen at 2000 μmol/mol

Methane is one of the major greenhouse gases that affect climate change. To mitigate anthropogenic CH4 emissions effectively, it is necessary to measure and monitor CH4 emissions from the production and transport of fossil fuels. Therefore, it is important for NMIs to demonstrate measurement equivalence for the standard gases of CH4.This is the third comparison on methane in nitrogen or air. The first comparison is the key comparison of CCQM-K82 (ambient level methane in air) and the second comparison is the supplementary comparison of APMP.QM-S7 (2000 μmol/mol methane in nitrogen). As a supplementary comparison, the purpose of this comparison is to study the comparability of CH4 standard gas mixtures at emission level (0.05 cmol/mol - 0.5 mol/mol in nitrogen or air). Furthermore, this comparison can provide a link to APMP.QM-S7 through KRISS who participated in both previous comparisons. In this comparison, KRISS prepared gas standards and sent to participants. Each participant measured the standard on their laboratory and reported their measurement results to KRISS according to the measurement protocol.This report describes the results of a supplementary comparison for methane in nitrogen at 2000 μmol/mol.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Investigation of adsorption characteristics of four toxic gases (nitric oxide, nitrogen dioxide, sulfur dioxide, and hydrogen chloride) on the inner surface of nickel-coated manganese steel cylinders and aluminum cylinders

ABSTRACT To develop standard toxic gas mixtures, it is essential to identify adsorption characteristics of each toxic gas on the inner surface of a gas cylinder. Thus, this study quantified adsorbed amounts of the four toxic gases (nitric oxide [NO], nitrogen dioxide [NO2], sulfur dioxide [SO2], and hydrogen chloride [HCl]) on the inner surface of aluminum cylinders and nickel-coated manganese steel cylinders. After eluting adsorbed gases on the inside of cylinders with ultrapure water, a quantitative analysis was performed on an ion chromatograph. To evaluate the reaction characteristics of the toxic gases with cylinder materials, quantitative analyses of nickel (Ni), iron (Fe), and aluminum (Al) were also performed by inductively coupled plasma optical emission spectrometry (ICP-OES). It was found that the amounts of NO, NO2, and SO2 adsorbed on the inner surface of aluminum cylinders were less than 1.0% at the level of 100 μmol/mol mixing ratio, whereas the signal for most heavy metal elements were below their respective detection limits. This study found that the amounts of HCl adsorbed on the inner surface of nickel-coated manganese steel cylinders were less than 5% at the level of 100 μmol/mol mixing ratio, whereas Ni (86 μmol) and Fe (28 μmol) were detected in the same cylinders. It was revealed that the adsorption mainly took place via the reaction of HCl with inner surface material of nickel-coated manganese steel cylinders. On the other hand, in the case of aluminum cylinders, the amounts of the adsorption were determined to be less than 1% at the level of HCl 100 μmol/mol mixing ratio, whereas most of Ni, Fe, and Al were detected at levels similar to their limits of detection. As a result, this study found that aluminum cylinders are more suitable for preparing HCl gas mixtures than nickel-coated manganese steel cylinders. Implications: To develop a standard toxic gas mixture, it is essential to understand the adsorption characteristics of each toxic gas inside a gas cylinder. It was found that the amounts of NO, NO2, and SO2 adsorbed inside aluminum cylinders were less than 1.0% at the level of 100 μmol/mol mixing ratio. The amounts of HCl adsorbed inside nickel-coated manganese steel cylinders were less than 5% at the level of 100 μmol/mol mixing ratio, whereas those inside aluminum cylinders were less than 1%, indicating that aluminum cylinders are more suitable for preparing HCl gas mixtures.

Verification of nitrous oxide primary standard gas mixtures by gas chromatography and cavity ring-down spectroscopy for ambient measurements in South Africa

Nitrous oxide (N2O) is an important greenhouse gas and is the third-largest contributor to global warming with a global warming potential (GWP) higher than that of carbon dioxide. Ambient N2O is monitored globally and described at nanomole per mole (nmol mol−1) levels. Metrologically traceable and highly accurate N2O gas standards are required to understand the behaviour of the greenhouse gases in the atmosphere and GWP. A group of primary standard gas mixtures (PSGMs) in aluminium cylinder material has been prepared in synthetic air for the calibration of analytical instruments for measurement of N2O at an ambient level. An automatic weighing system with a mass comparator and a fully automated circular rotary plate, as well as a gas filling station, was used in the preparation of the gas mixtures. Analytical methods such as gas chromatography coupled with micro-electron capture detector and cavity ring-down spectroscopy were adopted in the verification process. Four PSGMs in the final preparation step were used to analyse unknown background and filtered air samples at the ambient level. An expanded uncertainty relative to the gravimetric amount fraction was found to be 0.02 %. Results show that the background air samples lie within the calibration range with 329 to 330 nmol mol−1 obtained and 135 nmol mol−1 obtained for filtered air sample.

Using labelled internal standards to improve needle trap micro-extraction technique prior to gas chromatography/mass spectrometry

When working with humid gaseous samples, the amount of water vapour collected in a needle trap along with volatile analytes may vary from sample to sample and decrease during the storage. This has a major impact on desorption efficiency and recovery. We propose the addition of a labelled internal standards to nullify the effect of variable humidity on the analytical performance of needle trap micro-extraction combined with gas chromatography mass spectrometry. Triple-bed (Divinylbenzene/Carbopack X/Carboxen 1000) and single-bed (Tenax GR) needles were tested with standard gaseous mixtures prepared at different relative humidity levels (85%, 50% and 10%). The standard mixtures contained twenty-five analytes representative of breath and ambient air constituents, including hydrocarbons, ketones, aldehydes, aromatics, and sulphurs, in the concentration range 0.1–700 ppbv. The two needles showed different behaviours, as recovery was independent of humidity for single-beds, whereas a low recovery (10–20%) was observed when triple-beds trapped very volatile compounds at low humidity (e.g. pentane and ethanol, 10% relative humidity. Triple-beds showed an almost quantitative recovery (>90%) of all the analytes at 50% and 85% relative humidity. This big difference was probably due to the reduced action of water vapour pressure during the desorption step. The addition of 6D-acetone and 8D-toluene to the sorbent material before gas sampling and the normalization of raw data nullified this effect, thereby lowering the variations of analyte recovery at different humidity levels down to 20%. Internal standards were also exploited to limit within 10–20% alterations in peak areas of very volatile compounds during needle storage at room temperature. This variation may results from a loss of water vapour either retained from the sorbent material and/or condensed on triple-bed needle walls. After normalization, the inter- and intra-day precision were halved to 5% and 10% in the case of single-beds, respectively, and to 15% and 20% with three-beds. The addition of an internal standard to the sorbent helps to keep the overall analytical procedure under control and improves the reliability of needle trap micro-extraction for the analysis of volatile organic compounds at ultra-trace levels.

Trace impurities measurement in ultra-high purity gases and their uncertainties: case study on permanent gas impurities in pure nitrogen

Trace measurement for gas impurities plays an important role in the quality determination of pure-gases. High purity gases will certainly have a higher economic value than gases with lower purity, especially for the ultra-high purity gases used in the preparation of standard gas mixtures. These types of gases shall have a maximum limit for their impurities, which should be verified by a validated method. In this study, an experiment was conducted to determine the impurities in three cylinders of ultra-high purity nitrogen (UHP N2) gases using a validated gas chromatography equipped with pulse dicharge helium ionization detector (GC-PDHID) method. The impurities detected by the GC-PDHID in the aforementioned UHP N2 samples consist of argon (Ar), oxygen (O2), methane (CH4), and carbon monoxide (CO). Meanwhile, hydrogen (H2) and carbon dioxide (CO2) cannot be seen on the chromatogram, then assumed to be lower than the PDHID’s detection limit. Concentrations of the impurities, along with their uncertainties, were found to be 0.987 ± 0.104; 5.818 ± 0.807; 3.163 ± 0.449; and 1.289 ± 0.158 μmol/mol for Ar, O2, CH4, and CO, respectively for the first N2 cylinder. H2and CO2 were estimated to be half of the limit of detection, and H2O component was quoted from the UHP N2 manufacturer’s certificate of analysis. The other two N2 cylinders showed almost similar amounts of impurities. Based on the results, the actual purity for each of the three N2 gases can be estimated as 99.9987% mol/mol; 99.9987% mol/mol; and 99.9988% mol/mol. It is expected that the results of this study could useful as reference for both pure-gas manufacturers and consumers to properly determine the quality of their products.

Electrochemical preparation of standard gas mixtures using solid-state electrolyte membrane

A novel electrochemical method of preparation of standard gas mixtures for calibration of gas-analytical equipment with O2, H2 and CO was elaborated. Utilization of solid state electrolyte membrane allows to perform a nearly 100%-efficient electrochemical generation or conversion of the analyte and avoid some problems typical for liquid electrolytes, such as solvent evaporation and condensation at the inner walls of the gas tubes or deviations from the Faraday’s law. Analysis of uncertainties associated with the calibration procedure showed that the lowest systematic errors are achieved when the calibrant is generated during the electrolysis (i.e. anodic evolution of oxygen or cathodic generation of CO), and the major uncertainties are associated with operation of the flow controllers. For calibration with H2, where the calibrant is partially converted during the electrochemical process, the total uncertainty is essentially determined by molar fractions of the components in H2-Ar mixture, instrumental errors of the equipment, primarily by precision of mass-flow controllers or stability of the gas flow, and the initial flow rate of the calibrant-containing gas mixture. The relative total errors of calibration with oxygen are assessed to be 5–6%; similar uncertainties were calculated for analysis of oxygen content in standard gas mixtures by chromatography using the electrochemical method of calibration.

Performance of high rate MRPC with different gas mixtures

A Time Of Flight system (TOF) based on MRPC technology is widely used and plays an important role in modern high energy and nuclear physics experiments. With the increase of the energy and luminosity of the accelerators, many experiments have higher demand for a better resolution TOF detectors working in an high data rate environment, which undoubtedly represents a big challenge for this technology. FAIR-CBM is a typical high rate experiment and the particle rate of its TOF can reach 30 kHz/cm2. A new type of MRPC, built with low resistive glass with bulk resistivity of about 1010 Ohm cm, has been developed. The rate capability of this high rate MRPC can reach 70 kHz/cm2. The standard gas mixture for the high rate MRPC used for the FAIR-CBM-TOF is 90% C2H2F4, 5% i-C4H10 and 5% SF6. For the high rate MRPC used for the STAR-eTOF the gas mixture contains only two components, namely 95% C2H2F4 and 5% i-C4H10. In order to ensure the long time stability of the high rate MRPC and its use with different gas mixtures, we have studied the performance with different gas mixtures. The first measurements were performed with the standard gas mixture and different gas mixtures were tested by reducing the content of SF6. Three high rate MRPCs were tested at the same time for a cross-check, using a cosmic ray test-stand. The result of the test shows that the working point of the high rate MRPC moves toward a lower value of the high voltage by reducing the SF6 content in the gas mixture. The working point for a chamber efficiency of 95% without SF6 is about 800 V lower than the one with the standard gas mixture. Other properties such as time resolution, noise rate, dark current and cluster size have also been measured with different gas mixtures.