Rapid analysis of hydrocarbons and inert gases by a multidimensional gas chromatograph

A combination of a pressure switching system with multiple columns and photoionization detectors makes possible rapid analysis of a mixture of inorganic gases and hydrocarbons. Hydrocarbons are separated by a narrow bore capillary column. An alumina PLOT column is used for the separation of lower molecular weight hydrocarbons, especially C4 isomers, while a combination of a micro-packed column with Porapak N and a PLOT capillary column with Molecular Sieve 5A is used for the fast separation of inorganic gases. A photoionization detector is a powerful additional tool for organic gas analysis.     

Development of direct microwave desorption/gas chromatography mass spectrometry system for rapid analysis of volatile components in medicinal plants

A new direct microwave desorption–gas chromatography‐mass spectrometry method was developed for the analysis of the essential oils of medicinal plants. A homemade direct microwave desorption system was fabricated and used for the desorption of volatile components of medicinal herbs. The desorbed volatiles are transferred directly into the gas chromatography injector for analysis in a one‐step process. Approximately 0.3 g of the herb was needed for the desorption of samples in 60 s. In this study, more than 53 volatile compounds were identified and quantified for Echinophora platyloba DC as model herb sample. The results were found to be in good agreement with the conventional hydrodistillation extraction data. The described results show that direct microwave desorption is fast, simple, and easy to automate and requires only a small amount of sample. The results indicate that essential oil components valuable for varietal identification and characteristic of each variety analyzed when direct microwave desorption–gas chromatography‐mass spectrometry was used for analysis.     

固相萃取-毛细管气相色谱法检测淫羊霍等药用植物有机氯农药残留

建立了淫羊霍等药用植物中六六六及滴滴涕异构体残留量的毛细管气相色谱检测方法。样品采用微量化学法进行提取,固相萃取法净化,以不分流方式进样,用HP 5弹性石英毛细管柱程序升温分离样品,微电子捕获检测器检测,外标法计算其质量分数。结果表明,最小检测量为1.4×10-14～1.2×10-12g,加样平均回收率为92.16%～100.59%,相对标准偏差为0.5%～4.2%。该法各项技术指标均满足农药残留检测的要求。     

Miniaturized system of a gas chromatograph coupled with a Paul ion trap mass spectrometer

Miniature gas chromatography (GC) and miniature mass spectrometry (MS) instrumentation has been developed to identify and quantify the chemical compounds present in complex mixtures of gases. The design approach utilizes micro-GC components coupled with a Paul quadrupole ion trap (QIT) mass spectrometer. Inherent to the system are high sensitivity, good dynamic range, good QIT resolution, low GC flow-rates to minimize vacuum requirements and the need for consumables; and the use of a modular approach to adapt to volatile organic compounds dissolved in water or present in sediment. Measurements are reported on system response to gaseous species at concentrations varying over four orders of magnitude. The ability of the system to deal with complicated mixtures is demonstrated, and future improvements are discussed. The GC/QIT system described herein has a mass, volume and power that are, conservatively, one-twentieth of those of commercial off-the-shelf systems. Potential applications are to spacecraft cabin-air monitoring, robotic planetary exploration and trace-species detection for residual gas analysis and environmental monitoring.     

Micro-flame ionization detector with a novel structure for portable gas chromatograph

A micro-flame ionization detector (μ-FID) for portable gas chromatograph (GC) based on conventional mechanical fabrication techniques was developed and evaluated. Structure was redesigned and dimensions were optimized for best performance. Air is introduced from upper part of the detector, flowing downwards into the burning chamber along a narrow round gap between the collection electrode and the inner wall of the detector body, forming a uniform flow field around the burning jet. The lowest detection limit of the μ-FID was 5 × 10⁻¹³ g/s for n-decane, with a linear response range of five orders of magnitude. The consumption of gases is only 10 ml/min for hydrogen, and 120 ml/min for air, that is about 1/3 of the gases required for conventional FIDs. A comparative study between the μ-FID and commercial FID was also performed that proved the advantages of the μ-FID. The μ-FID is simple in structure, low heating power, and low consumption of gases that not only decrease the cost of running, but also increase the portability of GC for filed applications.     

Temperature‐programmed multicapillary gas chromatograph microcolumn for the analysis of odorous sulfur pollutants

We report the fabrication and performance of a silicon‐on‐glass micro gas chromatography eight‐capillary column based on microelectromechanical systems technology that is 50 cm long, 30 μm wide, and 300 μm deep. According to the theory of a gas chromatography column, an even gas flow among different capillaries play a vital role in the peak broadening. Thus, a flow splitter structure is designed by the finite element method through the comparison of the velocity distributions of the eight‐capillary columns with and without splitter as well as an open tubular column. The simulation results reveal that eight‐capillary column with flow splitters can receive more uniform flow velocity in different capillaries, hence decreases the peak broadening and in turn increases the separation efficiency. The separation experiment results show that the separation efficiency of about 22 000 plates/m is achieved with the chip column temperature programmed for analysis of odorous sulfur pollutants. This figure is nearly two times higher than that of the commercial capillary column coated the similar stationary phase. And the separation time of all the components in the microcolumn is less than 3.8 min, which is faster than the commercial capillary column.     

Fitting formula for the injection volume of a gas chromatograph for radio‐xenon sampling in the lower troposphere

GC is usually used for xenon concentration and radon removal in the International Monitoring System of the Comprehensive Nuclear‐Test‐Ban Treaty. In a gas chromatograph, the injection volume is defined to calculate the column capacity. In this paper, the injection volume was investigated and a fitting formula for the injection volume was derived and discussed subsequently. As a consequence, the xenon injection volume exponentially decreased with the column temperature increased, but exponentially increased as the flow rate increased.     

基于Unity 3D的气相色谱仪虚拟仿真实验系统的构建

虚拟仿真技术被广泛认为是一项重大技术进步,可以提供一种新颖的教学方式,能促进化学学习,打破传统教育方法的限制。三维交互式的气相色谱仪虚拟仿真实验系统使用当前主流的Unity 3D软件作为系统的主要开发工具。构建的系统主要包含仪器的动态原理展示、三维结构展示及仿真实验3部分。系统中的模型全部采用三维设计,场景逼真,能够全方位地向使用者展现真实仪器的外形及内部结构,令使用者如同置身于真实实验室中,获得身临其境的操作体验,从而更容易学习和掌握仪器组成、工作原理及相关的实验技能。系统不仅满足了仪器培训和化学实验教学的基本需求,而且对虚拟仿真技术在化学中的应用起了示范效应和推广作用。     

On-site environmental analysis by membrane extraction with a sorbent interface combined with a portable gas chromatograph system

A novel device, membrane extraction with a sorbent interface (MESI) coupled with a portable gas chromatograph (GC) system, has been developed. The main components of this system include a membrane module, a microtrap, and a control unit for the heater and cooler. The membrane module, as an on-line sample-introduction device for this system, can be manipulated in different configurations, allowing for the selective permeation of analytes across the membrane into the carrier/stripping gas. The analytes are trapped and concentrated onto a microtrap, which serves as an injector for gas chromatography separation. A concentration pulse of the trapped analytes is generated through direct electrical heating of the microtrap. The characteristics of this system have been explored, and its applicability and effectiveness have been demonstrated in field monitoring applications including the analysis of toluene in wastewater, Volatile organic compounds (VOCs) in laboratory air, and chloroform in swimming-pool water. This system is very promising, as it is a simple, fast, and portable tool for on-site process environmental monitoring.     

Adulteration or natural variability? enantioselective gas chromatography in purity control of essential oils

The potential of enantioselective capillary gas chromatography with modified cyclodextrins as chiral stationary phases for authenticity control is demonstrated for a selection of economically important essential oils. Adulteration can be easily detected in cases where enantiomerically pure constituents are present in natural oils. In cases of (naturally) varying enantiomeric compositions of chiral constituents, enantioselective gas chromatography may prove insufficient.     

Correlation of TLC/densitometry-data with capillary GC-data of some main volatile components of essential oils

The results of the densitometric and the capillary gas chromatographic investigations of numerous lavender oils of different origin and of essential oils of the woody group were correlated. Especially the main components, the monoterpenes linalool (¯1) and linalyl acetate (¯2), were quantified by densitometry with an average standard deviation of 6–7% in the examined oils. The use of TLC in combination with densitometry in the quantification of the main components to essential oils is thus a valuable addition to capillary gas chromatographic investigation. In addition to this, a useful and efficient alternative is given to groups specialized in TLC/densitometry to obtain data on such volatile compounds of essential oils during quantification. The use of TLC/densitometry thus combines the advantage of LC-with detection of also less volatile compounds—and the possibility of the parallel investigation of more samples in one step in a very efficient way.     

Characterization and Comparison of Tea Tree and Lavender Oils by Using Comprehensive Gas Chromatography

The essential oils from French lavender (Lavandula angustifolia) and tea tree (Melaleuca alternifolia) were separated by the two‐dimensional GC technique of comprehensive gas chromatography. A coupled column combination of non‐polar (5% phenyl equivalent) and polyethylene glycol phase columns was used to provide the desired resolution performance. By using a range of known standards, some of the peaks in lavender oil can be assigned. Some of these also occur in tea tree oil; however, from our knowledge of the major constituents in this oil and their relative retention behaviour, most of the major peaks may be tentatively assigned within the 2‐dimensional separation space. There appear to be elution patterns within the 2‐D space which should be useful in correlating retention with chemical and structural properties of the components, although this will require further evaluation. A range of coeluting peaks, which may not be so readily separated by using a single column capillary GC analysis, are resolved in the experiment described.     

制备气相色谱在挥发性成分分离中的应用研究进展北大核心CSCD

分析型气相色谱仪对低沸点易挥发的有机化合物展现出优异的分离性能,通过在其色谱柱末端加装馏分收集装置,建立了现代制备气相色谱(Prep GC)技术,该技术可用于挥发性成分的快速分离富集。制备气相色谱仪是由分析型气相色谱仪改装而来,其进样系统、分离系统、检测系统、馏分收集系统也在不断地优化升级,以提高目标化合物的回收效率和纯度。Prep GC与现代波谱技术(如紫外可见吸收光谱、红外吸收光谱、拉曼光谱、质谱、X射线衍射、核磁共振波谱)耦合,可对分离富集得到的目标化合物的结构进行精准确证。近年来,与Prep GC在各种挥发性成分分离中的应用相关的报道逐渐增多,展现出良好的应用前景。然而,Prep GC在分离过程中也存在着无法制备热敏性化合物、分离成本高、易引入外源性污染等问题。该文根据近年来国内外研究学者的相关研究工作,对制备气相色谱仪的结构及其在精油单体化合物、昆虫信息素、食品和植物挥发性成分、地质生物标志物及持久性环境污染物的分离等领域的应用研究进展进行综述。最后,还对Prep GC在挥发性成分分离中的应用进行了总结与展望,旨在为拓展Prep GC应用领域提供参考。     

Some applications of multidimensional gas chromatography to the enrichment of minor components in essential oil analysis

The use of multidimensional gas chromatography (MDGC) for the analysis of essential oils is gaining in importance. A rarely used application consists in the enrichment of minor components through a MDGC system provided with a cold trap between trap column and analytical column. Under suitable conditions, in fact, the cold-trap can store a trapped compound (or a fraction) for a long time. Consequently, the same fraction can be heart-cut from several successive chromatographic runs on the first column and stored together in order to accumulate trace compounds; afterwards the accumulated fraction can be injected in the analytical column. The possibilities of this technique will illustrated through some examples of analysis of complex essential oils.     

The preparation of immobilized polysiloxane coated on packings materials for high-pressure gas chromatography

Summary In high pressure gas chromatography efficient columns can be packed by the slurry packing technique. However, polysiloxane stationary phases like OV 101 and OV 3 dissolve in the packing liquids. In order to make them suitable for slurry packing these stationary phases have to be made insoluble. This immobilization is achieved by bonding the stationary phases to the surface by means of a high temperature treatment. Successive layers are applied by recoating and are immobilized by a cross-link reaction. A range of loading percentages from 4 upto 20 by weight could be prepared in this way. On the evaluated columns compounds like butanol and dioxane elute as rather symmetrical peaks with the correct values for the retention index, indicating the absence of adsorption effects. Efficiency is good and bleeding rate is low. The columns could be successfully used in the analysis of turpentines.     

Packed column SFC of gas oils part I: Hydrocarbon group separation using pure carbon dioxide

In this paper, the critical application of the ASTM method to hydrocarbon group separation in gas oils using conventional packed column SFC coupled to FID is described. Resolution of model compounds is studied using a recent commercial apparatus and the chromatographic conditions such as pressure, temperature, and density of the mobile phase and the nature of the stationary phase after FID detection conditions have been selected to give the best sensitivity. Three gas oils differing in composition (ratio arimatic/non-aromatic hydrocarbons)have been selected to evaluate the method for separation of the non-aromatic hydrocarbon group from mono-, di-, and polyaromatic hydrocarbons groups (sub-aromatic groups). The ASTM requiements for this analysis are very easy to obtain in adsorption chromatography. However, in adsorption or normal phase chromatography, SFC results cannot be perfect either for the quantification of aromatic and non-aromatic hydrocarbon fractions because there is still an overlap between the two groups (the separation is better in adsorption chromatography than in normal phase chromatography) or for sub-aromatic fractionation (the separation is better in normal phase chromatography than in adsorption chromatography); combination of both separation techniques only improves the sub-aromatic group fractionation. Thus, further enhancement of resolution for group and sub-group separation is needed.