Analysis Of Gas Mixtures Research Articles

Analysis of Gases by Raman Spectroscopy: Determination of Isotopic Composition of Hydrogen Mixtures (H2, D2 and T2)

The Raman spectroscopy is a very attractive method for real time, in-situ process monitoring and control in a tritium facility. From the viewpoint of safety and inventory of the tritium, the Raman spectroscopy allows the content of tritium in different points on a process to be measured. It’s a dynamic measurement with a short analytical period. Coupled with fiber optics, a Raman spectrometer allows on-line analysis of a tritiated process in a glove box with the spectrometer exterior to the glove box. This method should be applied to isotopic analysis of gas mixtures. The experimental results show that this technique is suitable for qualitative and quantitative analysis of tritiated gas mixtures.

Detection of characteristic metabolites of Aspergillus fumigatus and Candida species using ion mobility spectrometry - metabolic profiling by volatile organic compounds

Volatile metabolites of Aspergillus fumigatus and Candida species can be detected by gas chromatography/mass spectrometry (GC/MS). A multi-capillary column - ion mobility spectrometer (MCC-IMS) was used in this study to assess volatile organic compounds (VOCs) in the headspace above A. fumigatus and the four Candida species Candida albicans, Candida parapsilosis, Candida glabrata and Candida tropicalis in an innovative approach, validated for A. fumigatus and C. albicans by GC/MS analyses. For the detection of VOCs, a special stainless steel measurement chamber for the microbial cultures was used. The gas outlet was either attached to MCC-IMS or to adsorption tubes (Tenax GR) for GC/MS measurements. Isoamyl alcohol, cyclohexanone, 3-octanone and phenethylalcohol can be described as discriminating substances by means of GC/MS. With MCC-IMS, the results for 3-octanone and phenethylalcohol are concordant and additionally to GC/MS, ethanol and two further compounds (p_0642_1/p_683_1 and p_705_3) can be described. Isoamyl alcohol and cyclohexanone were not properly detectable with MCC-IMS. The major advantage of the MCC-IMS system is the feasibility of rapid analysis of complex gas mixtures without pre-concentration or preparation of samples and regardless of water vapour content in an online setup. Discrimination of fungi on genus level of the investigated germs by volatile metabolic profile and therefore detection of VOC is feasible. However, a further discrimination on species level for Candida species was not possible.

On reliability of neural network sensitivity analysis applied for sensor array optimization

Sensor arrays are nowadays first choice solution for low-cost and portable gas mixtures analysis systems. The key issue in construction of such systems is selection of sensors. The authors try to apply neural network sensitivity analysis for this task. The algorithm starts from huge set of sensors, which provides satisfying operation of the system, and then detects the most redundant elements, which may be removed without significant decrease of system accuracy. Eventually the small but efficient array of sensors is obtained. Authors present the method, propose some modifications and discuss problems with its application. Results of sensitivity analysis approach are compared with exhaustive search for the best set of sensors. The case study is quantitative analysis of volatile organic compounds mixtures by means of commercial, tin dioxide, TGS 800 series sensors characterized in in-house developed gas chamber.

A Wireless Electronic Nose System Using a Fe2O3 Gas Sensing Array and Least Squares Support Vector Regression

This paper describes the design and implementation of a wireless electronic nose (WEN) system which can online detect the combustible gases methane and hydrogen (CH4/H2) and estimate their concentrations, either singly or in mixtures. The system is composed of two wireless sensor nodes—a slave node and a master node. The former comprises a Fe2O3 gas sensing array for the combustible gas detection, a digital signal processor (DSP) system for real-time sampling and processing the sensor array data and a wireless transceiver unit (WTU) by which the detection results can be transmitted to the master node connected with a computer. A type of Fe2O3 gas sensor insensitive to humidity is developed for resistance to environmental influences. A threshold-based least square support vector regression (LS-SVR)estimator is implemented on a DSP for classification and concentration measurements. Experimental results confirm that LS-SVR produces higher accuracy compared with artificial neural networks (ANNs) and a faster convergence rate than the standard support vector regression (SVR). The designed WEN system effectively achieves gas mixture analysis in a real-time process.

Optical absorption method for the real-time component analysis of natural gas: Part 1. Analysis of mixtures enriched with ethane and propane

An optical method is developed for the real-time component analysis of natural gas mixtures. The method is based on the measurement of the absorption coefficients of the gas mixture at several wavelengths in the IR spectral range (7–14 μm). The resulting accuracy of the measurements of the methane, ethane, and propane contents in gas mixtures is sufficient for the monitoring of the component composition of natural gas in pipelines.

Quantitative analysis of CO-humidity gas mixtures with self-heated nanowires operated in pulsed mode

Self-heating effect in individual metal oxide nanowires can be used to activate their response to gases with power consumptions below tenths of microwatts. The thermal response time of these devices is extremely fast (a few milliseconds) and it makes it possible to observe the kinetics of the interactions between the gas molecules and the metal oxide. In this work we demonstrate that such effects enable an experimental methodology to improve the selectivity of metal oxide-based sensors based on the analysis of their fast response dynamics. Specifically, this work jointly analyzes the magnitude and response time of SnO2 nanowire-based sensors to carbon monoxide (CO) and humidity (H2O) mixtures, proving that a quantitative analysis of CO–H2O gas blends can be achieved by modulating their work temperature through the self-heating effect.

Study of the effect of the fractionation of gas mixtures in the pathway through a mass spectrometer

A novel method was proposed for the investigation of the fractionation effect in a mass spectrometer. Experimental data obtained on a MI-1201AGM mass spectrometer in the analysis of gas mixtures composed of perfluoromethylcyclohexane and uranium hexafluoride are presented.

Applicability of the quantum-chemical calculations of potential and electrooptical function parameters to the standardless spectrum analysis of heteroatomic organic compounds

The quantum-chemical calculation of potential and electrooptical function parameters for 32 heteroatomic (nitrogen-, oxygen-, and sulfur-containing) compounds was performed with the use of the B3LYP/6-311G(3df,3pd) basis set. With the use of a small correction of the potential function with unified scaling factors, the calculated frequencies and absolute intensities of fundamental absorption bands agreed satisfactorily with the experimental values. The average and standard deviations of calculated and experimental frequencies were no higher than the half widths of their absorption bands. The results suggest the applicability of these calculations to the standardless spectrum analysis of gas mixtures.

Development of a IRSN code for dust mobilisation problems in ITER

The analysis of accident scenarios in the ITER Fusion facility such as loss of vacuum accidents (LOVA) or ingress of coolant accidents (ICE) is of primary importance in order to evaluate pressure loads generated by a potential dust explosion or mobilisation. Thus the DUST code for simulation of dust mobilisation has been developed in close collaboration between IRSN (France) and the Technical University of Cartagena (Spain), on the basis of the CAST3M code developed at the Commissariat à l’Energie Atomique (CEA, France). A high dilute model for the analysis of particle and gas mixtures has been implemented in the code. This type of mixtures is expected in the case of a LOVA inside ITER. The code will permit the analysis of dust spatial distribution, remobilisation and entrainment, and explosion. Special attention is paid to the study of the closure relationships which characterise the physical phenomena involved in this sort of problems and a model based on the force balance has been implemented as well. The implementation of the adhesion/re-suspension model is carefully described. To test the code qualitatively, two benchmarks have been studied taking into account the influence of different parameters. Some conclusions are finally drawn.

QEPAS for chemical analysis of multi-component gas mixtures

A gas sensor based on quartz-enhanced photoacoustic spectroscopy and using near-infrared, fiber-coupled diode lasers as an excitation source was developed for chemical analysis of gas mixtures containing H2S, CO2, and CH4 at concentrations from 0 to 100%. Analysis of physical phenomena affecting the sensor operation is performed, the sensor performance is evaluated, and simple algorithms are developed to derive concentrations of the gases from detected electrical signals.

In Situ EELS Analysis of Gas Mixtures in the Environmental TEM

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Laser-induced breakdown spectroscopy in gases using ungated detection in combination with polarization filtering and online background correction

Quantitative and fast analysis of gas mixtures is an important task in the field of chemical, security and environmental analysis. In this paper we present a diagnostic approach based on laser-induced breakdown spectroscopy (LIBS). A polarization filter in the signal collection system enables sufficient suppression of elastically scattered light which otherwise reduces the dynamic range of the measurement. Running the detector with a doubled repetition rate as compared to the laser online background correction is obtained. Quantitative measurements of molecular air components in synthetic, ambient and expiration air are performed and demonstrate the potential of the method. The detection limits for elemental oxygen and hydrogen are in the order of 15 ppm and 10 ppm, respectively.

A Concept of a Sensor System for Determining Composition of Organic Solvents

This paper presents the results of work on a gas sensor system for determining qualitative and quantitative composition of organic solvents. The system performs the analysis of gaseous mixtures, which are obtained by evaporating liquid solvents and therefore directly represent their composition. The system utilizes gas sensor array, which is built of Taguchi gas sensors (TGS). It provides patterns of measured solvents which are analyzed by pattern recognition module. The module employs multivariate statistical tools like discriminant function analysis (DFA) and partial least squares (PLS) regression. The determination of solvent composition is organized in a hierarchical structure. The concept of the system was experimentally verified using the example of two-component solvents. It was here demonstrated that the proposed system is capable of determining qualitative and quantitative composition of liquid solvents.

Metal-modified and vertically aligned carbon nanotube sensors array for landfill gasmonitoring applications

Vertically aligned carbon nanotube (CNT) layers were synthesized on Fe-coatedlow-cost alumina substrates using radio-frequency plasma enhanced chemicalvapour deposition (RF-PECVD) technology. A miniaturized CNT-based gas sensorarray was developed for monitoring landfill gas (LFG) at a temperature of150 °C. The sensor array was composed of 4 sensing elements with unmodified CNT, and CNTloaded with 5 nm nominally thick sputtered nanoclusters of platinum (Pt), ruthenium (Ru)and silver (Ag). Chemical analysis of multicomponent gas mixtures constituted ofCO2,CH4,H2,NH3, COand NO2 has been performed by the array sensor responses and pattern recognition based onprincipal component analysis (PCA). The PCA results demonstrate that themetal-decorated and vertically aligned CNT sensor array is able to discriminate theNO2 presence in the multicomponent mixture LFG. TheNO2 gas detection in the mixture LFG was proved to be very sensitive, e.g.: theCNT:Ru sensor shows a relative change in the resistance of 1.50% and 0.55% forNO2 concentrations of 3.3 ppm and 330 ppb dispersed in the LFG, respectively, with a wideNO2 gas concentration range measured from 0.33 to 3.3 ppm, at the sensor temperature of150 °C. The morphology and structure of the CNT networks have been characterized byscanning electron microscopy (SEM), transmission electron microscopy (TEM)and Raman spectroscopy. A forest-like nanostructure of vertically alignedCNT bundles in the multi-walled form appeared with a height of about 10µm and a single-tube diameter varying in the range of 5–35 nm. The intensity ratio of the Ramanspectroscopy D-peak and G-peak indicates the presence of disorder and defects in the CNTnetworks. The size of the metal (Pt, Ru, Ag) nanoclusters decorating the CNT top surfacevaries in the range of 5–50 nm. Functional characterization based on electrical chargetransfer sensing mechanisms in the metal-modified CNT-chemoresistor array demonstrateshigh sensitivity by providing minimal sub-ppm level detection, e.g., download up to 100 ppbNO2, at the sensortemperature of 150 °C. The gas sensitivity of the CNT sensor array depends on operating temperature, showing alower optimal temperature of maximum sensitivity for the metal-decorated CNT sensorscompared to unmodified CNT sensors. Results indicate that the recovery mechanisms in theCNT chemiresistors can be altered by a rapid heating pulse from room temperature to about110 °C. A comparisonof the NO2 gas sensitivity for the chemiresistors based on disorderly networked CNTs and verticallyaligned CNTs is also reported. Cross-sensitivity towards relative humidity of the CNTsensors array is investigated. Finally, the sensing properties of the metal-decorated andvertically aligned CNT sensor arrays are promising to monitor gas events in the LFG forpractical applications with low power consumption and moderate sensor temperature.

Multivariate curve resolution applied to temperature-modulated metal oxide gas sensors

Metal oxide (MOX) gas sensors have been widely used for years. Temperature modulation of gas sensors is as an alternative to increase their sensitivity and selectivity to different gas species. In order to enhance the extraction of useful information from this kind of signals, data processing techniques are needed. In this work, the use of self-modelling curve resolution techniques, in particular multivariate curve resolution-alternating least squares (MCR-ALS), is presented for the analysis of these signals. First, the performance of MCR in a synthetic dataset generated from temperature-modulated gas sensor response models has been evaluated, showing good results both in the resolution of gas mixtures and in the determination of concentration/sensitivity profiles. Secondly, experimental confirmation of previously obtained conclusions is attempted using temperature-modulated MOX sensors together with MCR-ALS for the analysis of carbon monoxide (CO) and methane (CH4) gas mixtures in dry air. Results allow confirming the possibility of using the proposed approach as a quantitative technique for gas mixtures analysis, and also reveal some limitations.

Technical approaches in the mass spectrometric analysis of hydrogen and helium isotopes

A method of mass spectrometric analysis of gas mixtures of hydrogen and helium isotopes on low-resolution units is proposed. The method is based on the dependence of the ion current intensity on the partial pressure of the gas in the puffing system of the mass spectrometer. The appropriate laboratory procedure for performing the mass spectrometric analysis with simultaneous recording of the mass spectrum and absolute gas pressure in the puffing system of the mass spectrometer is designed. It was shown that it is possible to identify completely overlapping peaks of ion currents of components of the gas mixture, and this is confirmed by the measurement results.

Wireless electronic nose system for real-time quantitative analysis of gas mixtures using micro-gas sensor array and neuro-fuzzy network

A wireless electronic nose system (WENS) is designed for the real-time quantification of ammonia (NH3), hydrogen sulfide (H2S), and their mixtures. The WENS hardware consists of a microcontroller for obtaining measurement data from a micro-gas sensor array, and an RF transceiver for transmitting the data sets to a master sensor node. Meanwhile, the WENS software analyses the binary gas mixtures using a fuzzy ARTMAP classifier and a fuzzy ART-based concentration estimator with multiplicative drift correction based on reference gases. A virtual instrument is developed in the LabVIEW environment for monitoring the analyzed gas mixtures. The performance of the proposed WENS is also assessed and compared with the minimum and product inference methods. The proposed WENS adopting the weighted inference method produces the best concentration estimations as regards the root mean square error.

Gas sensors in a dynamic operation mode

Temperature-modulated metal-oxide gas sensors exhibit different behavior from sensors operating in an isothermal mode. Such temperature-modulated sensor response is affected by stimulating excitation, sensor structure, sensitive layer preparation etc. Due to different reaction rates dependent on modulating temperature, the response yields a special signature for the investigated gas atmosphere. The response can be analyzed using different pattern recognition and artificial intelligence methods. As a result, one can achieve an improvement of selectivity and drift reduction. It is also possible to accomplish a qualitative and quantitative analysis of gas mixtures using a single sensor. One of the most important issues is the selection of proper parameters of a signal that modulates the heater temperature. The range of temperature variations should be chosen according to the gas type and its concentration to achieve good sensitivity. The period of the excitation signal also influences the sensor response and has to be chosen above the value of gas/semiconductor reaction time constant. In this paper the authors describe the ways in which a temperature-modulating signal is selected and discuss the possibility of using a dynamic sensor response to quantitatively determine the concentrations of two gases in a mixture with the help of one sensor.

Resolution and calibration requirements for a time-of-flight mass spectrometer for analyzing gaseous fuel mixtures of a thermonuclear reactor

It is shown that to a large extent the isotopic and chemical analysis of gas mixtures can be performed using a time-of-flight mass spectrometer (mass reflectron), operating in a mode of synchronous detection to eliminate or substantially reduce the background current due to the beta decay of tritium nuclei. To this end, a mass reflectron with resolution ∼600 at 10% height of the peak near 3–4 amu has been developed and built and is now under investigation. Such resolution makes it possible to calibrate instruments by using special gas mixtures, study the relations of the atomic, molecular, associated, and trimer peaks of hydrogen isotopes under different conditions, and on this basis to develop a method for calculating the composition of real fuel mixtures from the experimental mass spectra. The apparatus also permits determining the composition of impurities over a wide range of their concentration in the entire mass range to a high degree of accuracy.

MEMS-based multi-inlet/outlet preconcentrator coated by inkjet printing of polymer adsorbents

Preconcentration plays a major role in the quantitative analysis of gas mixtures. Using microfabrication technology, a microthermal preconcentrator (μTPC) device with high-aspect-ratio 3D structures (240 μm) is presented. The silicon-glass die has outer dimensions of 7 mm × 7 mm, total inner surface area of ∼200 mm2, and a total inner volume of ∼6.5 μL. The μTPC has on-chip thermal desorption capability and comprises more than 3500 micropillars with dimensions of 27 μm × 115 μm × 240 μm. To enhance preconcentration capability, the device was coated with a uniform polymer adsorbent film using a high coverage coating method based on the principle of inkjet printing technology and heated with off-board high-performance ceramic heater. The effect of the distributed inlet/outlet on the μTPC performance has been explored using computational fluid dynamics (CFD) analysis and verified by experimental results. The μTPC demonstrated a very sharp reproducible desorption peak which is needed for fast analytical analysis. A concentration factor of 1000 using Tenax TA adsorbent was achieved. The μTPC was used as a gas chromatography (GC) injector to demonstrate its capability in concentrating a dilute multi-compound hydrocarbon mixture into a sharp pulse suitable for gas chromatographic analysis. The performance of the μTPC was evaluated in terms of adsorption capacity, pillar packing density, and inlet pressure. It was found to be in agreement with the breakthrough model.