Fast gas chromatography: packed column solvating gas chromatography versus open tubular column gas chromatography

Packed capillary column solvating gas chromatography (SGC) and open tubular column gas chromatography (GC) were compared with respect to their potentials for fast separations. A recently introduced "universal" peak capacity equation was used to compare the performance of these two methods. The effects of various factors on peak capacity were investigated. Results demonstrate that retention factor and column efficiency are the main factors affecting peak capacity for fast separations. Packed columns produce both high retention factors and high selectivities. While high efficiencies and high peak capacities can be demonstrated by both techniques, open tubular column GC can surpass packed capillary column SGC in both measurements, except for the case of the analysis of simple mixtures in short analysis times, where retention factor and selectivity become important. Practical aspects such as pressure drop and sample capacity are compared for SGC and open tubular column GC. It was found that packed column SGC demonstrates higher sample capacities, but requires much higher column inlet pressures than open tubular column GC. A variety of mobile phases can be used for packed column SGC, which can provide high solvating power for large and polar compounds.     

Determination of the gas chromatographic gas hold-up time

Summary New versions are suggested for the gas hold-up time calculation in gas chromatography. The results are compared with those obtained by using other methods. The advantages of the suggested ways of calculation are pointed out.     

Water vapor as a carrier gas in capillary gas chromatography

The use of water vapor as carrier gas in capillary chromatography is analyzed. Under equivalent conditions, a comparison of water vapor and helium as a mobile phase was performed during the separation of diesel fuel components. The advantage of water vapor was demonstrated. The resolutions of peaks were calculated for a pair of substances, C₁₈-iso and C₂₀ (4.4 for water vapor and 3.9 for helium). The Van Deemter dependences were measured, and it was demonstrated that the substantially lower viscosity of the water vapor compared to helium makes it possible to perform the separation of substances in a broader range of linear velocities, comparable to hydrogen used as mobile phase. The prospects for using water vapor was demonstrated in chromatographic analysis of hydrocarbons.     

二维气相色谱法分析天然气水合物区沉积物间隙水中示踪气体的浓度

利用微流路控制技术中心切割装置(Deans Switch)、两根色谱柱(PoraPLOT Q和Molsieve 5A)和3个检测器(脉冲氦离子化检测器、火焰光度检测器、热导检测器),建立了一种二维气相色谱分析系统,实现了海洋中多种示踪气体组分(氢气、甲烷、二氧化碳、硫化氢)的同时分析和精确测定。氢气、甲烷、二氧化碳、硫化氢的含量分别在2～1030、0.6～501、120～10500和0.2～49.1 μmol/mol范围内的校正曲线线性关系良好,检出限分别为0.51、0.17、82和0.08 μmol/mol,10次重复测定含量的相对标准偏差均小于10%。通过对南海天然气水合物区沉积物间隙水顶空气的测定,表明该方法方便、灵敏、可靠,易于实现海上现场测定;与以往采用多种分析方法分别测定示踪气体相比,大大节省了样品量。该方法适用于海洋天然气水合物、海底热液等资源的调查和海洋溶解态气体的研究等。     

Capillary gas chromatography of amines with ammonia as carrier gas

The use of ammonia as a carrier gas for the chromatography of aliphatic and aromatic amines has been investigated. As compared to nitrogen, ammonia gave drastically improved peak symmetry and lower capacity factors (k′) for primary and secondary amines on polar (Polyethylene glycol) and medium Polar (methylphenylcyanopropylsilicone) stationary Phases. The effect of ammonia was more Pronounced at low column temperatures. Considerably better detection limits of primary and secondary amines were obtained with ammonia as carrier gas than with nitrogen. No detrimental effects of using ammonia were observed on the gas chromatograph or on the columns over a period of about one year.     

生物质合成气一步法合成LPG的实验研究

由生物质气化合成液体燃料(甲醇、二甲醇和低碳烃类),是理想的碳中性绿色燃料,将其用作城市交通和民用燃料,已经引起全世界的广泛关注.[1,2]     

Formation and decomposition of gas hydrates of natural gas components

Based on our theoretical and experimental work carried out during the last decade, our understanding of the thermodynamics and the kinetics of formation and decomposition of gas hydrates is presented. Hydrate formation is modelled as a crystallization process where two distinct processes (nucleation and growth) are involved. Prior to the nucleation the concentration of the gas in the liquid water exceeds that corresponding to the vapor-liquid equilibrium. This supersaturation is attributed to the extensive structural orientation in the liquid water and is necessary for the phase change to occur. The growth of the hydrate nuclei or the decomposition of a hydrate particle are modelled as two-step procedures. Only one adjustable parameter for each hydrate forming gas is required for the intrinsic rate of formation or decomposition. In addition the inhibiting effects of electrolytes or methanol on hydrate formation are discussed and experimental data on methane gas hydrate formation in the presence of aqueous solutions of 3% NaCl and 3% NaCl + 3% KCI, are presented along with the predicted values. Finally, the relevence of the ideas to the technological implications of gas hydrates as well as areas where future research is needed are discussed.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Applications of gas chromatography and gamma spectrometry to fission gas measurements

A gas sampler with lead shield has been designed for transferring the grab gas sample taken from the sampling station of Taiwan nuclear power reactor. The methods involving gas chromatography and gamma spectrometry have been developed for the determination of fission gases. A gas chromatograph equipped with TCD was used for measurement of gas composition. Column requirements are identified and optimum operating conditions are discussed. A single analysis is completed within 25 minutes for all of the gas constitutents and 12 minutes for only Xe and Kr. The detection limit is 0.005 mm partial pressure for Kr and Xe and a precision of ±1% relative is achieved for all the sample constituents. Combined error determinations for the method denote an attainable accuracy of less than ±2% for constituents at a sample pressure above 10 mm. Mixing and dispensing of the radioactive gases were carried out in a special gas mixing line. In experiment, calibration factors for measurement of¹³³Xe and⁸⁵Kr in ampules are determined in an isotope calibrator and by Ge(Li) gamma ray spectrometry. The relative precisions of 0.14% and 0.5% are readily achieved for⁸⁵Kr and¹³³Xe, respectively. The calibration uncertainty in⁸⁵Kr measurement is 0.4%.     

Fluctuation-enhanced gas sensing

The sensitivity of gas sensors was earlier measured by classical method-comparison the resistance of sensors in gas media and air. Here we reported results of the study of low-frequency noise characteristics of sensors. We compare data for different Figaro TGS sensors as well as our sol-gel H₂ tin dioxide and porous silicon sensors. The study was performed in dry air and in a mix of dry air with carbon monoxide, hydrogen and alcohol of different concentrations. Higher sensitivity of spectral dependence of noise (SDN) to gas concentration in comparison with classical method of the measurements of gas sensing by a change in the Ohmic resistance part of current-voltage characteristics of samples allows using such SND powerful method for determination of gas concentration in the air or environment.     

Rapid analysis of coke oven gas by capillary gas chromatography

A porous layer open tubular (PLOT) column has been used for monitoring the light hydrocarbons and permanent gases produced in coking plants. The method, which offers a simple alternative to traditional multi column techniques, entails a single injection on to a Carboplot 007 capillary column and simultaneous thermal conductivity and flame ionization detection. The simplified approach proposed is restricted to coke oven gas analysis: application to other gas mixtures has not been considered. The reliability of this procedure compares favorably with that of traditional methods; the technique is also much less time-consuming: seven individual gases can be determined on-line every fifteen minutes. Primary and secondary gas standards were used to determine response curves for the gases. The method also facilitates reliable calculation of heat values associated with the burning of the fuel gas mixtures.     

Wrong gas/liquid partition data by gas chromatography

In a paper published in 1992 [K.S. Reddy, J.-Cl. Dutoit, E.sz. Kováts, Pair-wise interactions by gas chromatography. I. Interaction free enthalpies of solutes with non-associated primary alcohol groups, J. Chromatogr. 609 (1992) 229] retention indices and standard chemical potential differences (SPOT-s) are given for about 160 solutes on a liquid branched paraffin hydrocarbon of the carbon number, z = 78. For the temperature dependence of the SPOT-s the proposal of Kirchhoff was accepted i.e. that at higher temperatures the molar heat capacity difference of the solute between the gas phase and the solution is nearly constant in a broad temperature range. The data were determined under conditions where the effect of adsorption could be neglected. By comparing the published data with those determined on another branched paraffin of the carbon number, z = 87 [F. Riedo, D. Fritz, G. Tarján, E.sz. Kováts, A tailor-made C87 hydrocarbon as a possible non-polar standard stationary phase for gas chromatography, J. Chromatogr. 126 (1976) 63] it is shown that the reported thermodynamic constants of solutes determined experimentally at higher temperatures (the group "H") are wrong on C78. In the present paper, the method of correction and the resulting corrected data are given. In later papers retention data are given on eight polar derivatives of the hydrocarbon C78 relative to those measured on the nonpolar standard [R. Cloux, G. Défayes, K. Fóti, J.-Cl. Dutoit, E.sz. Kováts, Pair-wise interactions by gas chromatography. III. Synthesis of isosteric stationary phases for gas chromatography, Synthesis (1993) 909; G. Défayes, K.S. Reddy, A. Dallos, E.sz. Kováts, Pair-wise interactions by gas chromatography. V. Interaction free enthalpies of solutes with primary chloro- and bromo-alkanes, J. Chromatogr. A 699 (1995) 131; K.S. Reddy, E.sz. Kováts, Pair-wise interactions by gas chromatography. II. Sociation free enthalpies of some hydrogen bonding solutes with non-associated primary alcohol groups, Chromatographia 34 (1992) 249; K.S. Reddy, R. Cloux, E.sz. Kováts, Pair-wise interactions by gas chromatography. IV. Interaction free enthalpies of solutes with trifluoromethyl-substituted alkanes, J. Chromatogr. A 673 (1994) 181; K.S. Reddy, R. Cloux, E.sz. Kováts, Pair-wise interactions by gas chromatography. VI. Interaction free enthalpies of solutes with primary methoxyalkane, cyanoalkane and alkanethiol groups, J. Chromatogr. A 704 (1995) 387; A. Dallos, A. Sisak, Z. Kulcsár, E.sz. Kováts, Pair-wise interactions by gas chromatography. VII. Interaction free enthalpies of solutes with secondary alcohol groups, J. Chromatogr. A 904 (2000) 211]. Obviously, the same data which are wrong in the nonpolar standard are also wrong in these solvents. The corrected data in the polar solvents are given in supplementary tables.     

Inorganic gas chromatography

Summary The possibilities of using gas-solid chromatography as a method for the separation of trace amounts of various elements such as volatile chlorides or oxychlorides are investigated. The use of quartz as the column material and graphite, quartz or quartz coated with different ionic chlorides of low volatility as the stationary phase allows the use of temperatures up to 1100 K and consequently the separation of many elements as chlorides. The theory of linear equilibrium chromatography is applied successfully to the investigation of the influence of temperature and the type of solid (stationary) phase, in order to optimize separations. The dependence of the peak width on the various parameters is more complex, but several general principles can be derived from the experimental results. From these data physicochemical properties of the adsorbate-adsorbent systems investigated can be derived, and the optimum conditions for isothermal separations can be estimated.     

Hydrate capture CO2 from shifted synthesis gas,flue gas and sour natural gas or biogas

CO₂ capture by hydrate formation is a novel gas separation technology, by which CO₂ is selectively engaged in the cages of hydrate and is separated with other gases, based on the differences of phase equilibrium for CO₂ and other gases. However, rigorous temperature and pressure, high energy cost and industrialized hydration separator dragged the development of the hydrate based CO₂ capture. In this paper, the key problems in CO₂ capture from the different sources such as shifted synthesis gas, flue gas and sour natural gas or biogas were analyzed. For shifted synthesis gas and flue gas, its high energy consumption is the barrier, and for the sour natural gas or biogas (CO₂/CH₄ system), the bottleneck is how to enhance the selectivity of CO₂ hydration. For these gases, scale-up is the main difficulty. Also, this paper explored the possibility of separating different gases by selective hydrate formation and reviewed the progress of CO₂ separation from shifted synthesis gas, flue gas and sour natural gas or biogas.     

Configuration and optimization of semiconductor gas sensors as gas chromatographic detectors

A tin oxide, gas-sensitive semiconductor sensor was configured as a gas chromatographic detector and its performance was optimized. Two sensor housings were compared but little difference was found in performance. The flow rate and temperature of the column and the internal heater voltage of the sensor affected both the sensitivity and peak shape. The temperature of the sensor surface was the most critical parameter. Optimal conditions for the gas chromatographic detection of a mixture of alkanes (C₁–C₅) and hydrogen were identified by using the simplex technique. The detection limit for hydrogen was improved by a factor of five to 20 ppb (v/v), illustrating the value of optimization and the excellent sensitivity of the detector. It is concluded that semiconductor gas sensors offer significant advantages as gas chromatographic detectors for the determination of reducing gases.     

Dual-purpose gas chromatographic injection device for pressurized liquid and gas injection

A dual-purpose gas chromatographic injection device, capable of injecting pressurized liquid sample of up to 5000 psig and gas sample with a volume as high as 5000 μL, has been successfully developed and implemented. The injection device is synergized by the effectiveness of a classical flash vaporization of a syringe injection and the reliability of a proven rotary valve. Depending on the matrix involved, this injection device employs either a commercially available four-port internal valve for liquid sampling or a six-port external valve for gas sampling, a modified removable needle used in standard liquid syringe, and an auxiliary flow stream that can be either mechanical or electronic flow controlled for solute transfer. For pressurized liquid, the device was found suitable of up to nC₁₆ hydrocarbon with no observable carry-over despite the injection device was operating at ambient temperature. A relative standard deviation of less than 2% (n = 20) was obtained for hydrocarbon compounds ranging from nC₈ to nC₁₆. For gas injection, the device performed well even under difficult chromatographic conditions such as with a low column inlet pressure of less than 1 psig. A relative standard deviation of less than 0.5% (n = 10) was obtained for reactive sulfur compounds such as alkyl mercaptans. The device can be operated manually or automated with pneumatic or electrical actuator, is platform neutral, and can be moved amongst instruments without hardware modification as well as implemented for on-line or in situ applications. In this paper, the utility of the device was also demonstrated with selected GC applications of industrial significance.     

Clinical applications of gas chromatography and gas chromatography-mass spectrometry of steroids.

This review article underlines the importance of gas chromatography-mass spectrometry (GC-MS) for determination of steroids in man. The use of steroids labelled with stable isotopes as internal standard and subsequent analysis by GC-MS yields up to now the only reliable measurement of steroids in serum. Isotope dilution GC-MS is the reference method for evaluation of routine analysis of serum steroid hormones. GC-MS is an important tool for detection of steroid hormone doping and combined with a combustion furnace and an isotope ratio mass spectrometer the misuse of testosterone by athletes can be discovered. Finally the so called urinary steroid profile by GC and GC-MS is the method of choice for detection of steroid metabolites in health and disease.     

CO2 removal from synthetic natural gas for city gas use

Membrane-based gas separation has been applied for carbon dioxide (CO₂) removal from commercial city gas supply plants in Japan. This paper provides the relationship between methane reforming process, design of two-stage membrane process and their optimization.     

New approaches on gas phase molecular absorption spectrometry detection in gas chromatography

A hyphenated technique for coupling a spectrophotometric detector to a gas chromatograph with a packed column is described. The packed column was connected directly to the flow cell (path length 1 cm) which was placed in a UV-visible molecular absorption spectrophotometer with diode array detector. This detection system was employed for separating and determining benzene, toluene, 1,4-xylene, 1,2-xylene and mesitylene. Molecular absorption spectra of all the separated compounds have also been obtained. A new possibility for coupling capillary gas chromatography and gas phase molecular absorption spectrometry is currently being tested. In this new case, two fibre optics are used and the measurement is performed in the capillary column.     

New approaches on gas phase molecular absorption spectrometry detection in gas chromatography

A hyphenated technique for coupling a spectrophotometric detector to a gas chromatograph with a packed column is described. The packed column was connected directly to the flow cell (path length 1 cm) which was placed in a UV-visible molecular absorption spectrophotometer with diode array detector. This detection system was employed for separating and determining benzene, toluene, 1,4-xylene, 1,2-xylene and mesitylene. Molecular absorption spectra of all the separated compounds have also been obtained. A new possibility for coupling capillary gas chromatography and gas phase molecular absorption spectrometry is currently being tested. In this new case, two fibre optics are used and the measurement is performed in the capillary column.     

裂解气相色谱-质谱法分析裂解气压缩机垢样的组成

采用裂解气相色谱-质谱联用技术对大庆石化公司裂解气压缩机EC301不同压缩段的垢样进行分析。实验使用了RJ-1型管炉式裂解器,在500℃下对垢样进行裂解,色谱柱为60 m DB-1型毛细管色谱柱,质谱采用电子轰击电离源,电离能70 eV。研究表明,垢样的形成与环戊二烯密切相关。裂解气相色谱-质谱法可以作为分析该垢样成因的有效手段。