Application of capillary gas chromatography in the analysis of hydrocarbons in the environment

Summary Hydrocarbons are emitted into the environment in quantity and diversity. Some of these can be detrimental in low concentration, many can be active in photochemical smog production. For combatment there is also interest in the sources of hydrocarbons in the atmosphere. For source recognition fine-structured chromatographic fingerprints are essential. This also holds for oil pollution. A complicating factor in the determination of hydrocarbon pollutants may arise from the occurrence of recently biosynthesized hydrocarbons. For distinguishing between these two types the application of capillary gas chromatography is preferred to packed column gc. It will be clear that the application of capillary gc in the analysis of hydrocarbons in the environment is of great practical value. The modified Grob method used by us for the analysis of hydrocarbons in air is discussed. For the characterization and source recognition of oil pollution in water and soil application of capillary gc fingerprinting is essential; in this way valuable information can be gathered about weathering of oil pollution. Sources of oil pollution in water areas and harbour regions can be traced in certain cases. Also the possibility of measurement of residence time is present. Typical examples are given.Publication No. 601 of the TNO Research Institute for Environmental Hygiene.     

The critical gas saturation in a porous medium in the presence of gravity

The critical gas saturation, S(gc), denotes the volume fraction of the gas phase at the onset of bulk gas flow during the depressurization of a supersaturated liquid in a porous medium. In the absence of gradients due to viscous or gravity forces, S(gc) is controlled by nucleation, capillary forces, and the rate of decline of the supersaturation. In this paper we address one important additional effect, that of buoyancy. We use 2-D pore-network simulations, based on invasion percolation in a gradient (IPG), and corresponding scaling relations to obtain the dependence of S(gc) on the gravity Bond number, B, under conditions of slow growth, namely when mass transfer is sufficiently fast. The critical gas saturation approaches two plateau values at low and high Bond numbers. In the in-between region it scales as a power law of B, which for a 2-D lattice is S(gc) approximately B(-0.91).     

Practical aspects of the dependence of polarity on temperature

Summary It is not commonly appreciated that retention indices are temperature dependent. It is even less common to express this fact in more practical terms by saying that polarity is temperature dependent. Although the meaning of both statements is identical, we believe the second to be particularly relevant, since the majority of practical gas chromatographers tends to handle polarity as an invariable characteristic of a stationary phase.The variability of polarity with temperature is the major source of inadequate reproducibility of exact finger-printing, this particularly when gc/ms traces have to be compared to those obtained by pure gc. On the other hand, the temperature dependence provides a practical means to optimize the polarity of a given column for a given analysis. Film thickness is an essential parameter in this context because of its influence on column temperature and, therefore, on column polarity.     

Direct injection of large sample volumes into capillary columns with packed column injector

A direct injection method for large volume samples which avoids severe tailing of the solvent peak has been developed using a packed column injector (up to 100 μl) leading into an ordinary capillary column (0.3 mm i.d.). Modifications are made to the cooler zones of the inlet port and on the carrier gas flow control system. This injection technique is based on the effective use of phase soaking and cold trapping using a retention gap. The large volume of solvent vapor is rapidly purged out of the injector with a higher flow of carrier gas while the solutes trapped at the head of the column are subsequently analyzed with another optimum flow rate. The proposed carrier gas flow regulation system is also compared with conventional split/splitless injection methods.     

Capillary gas chromatography of some metal acetylacetonates

Summary The retention and resolution of simple mixture of Al(III), Cr(III), Co(III), and Fe(III) acetylacetonates were investigated on capillary columns coated with methyl and methyl phenyl silicones (OV-1 or OV-17) used as the stationary phase, at different column temperatures and carrier gas flow rates. Successful elution and good resolution were obtained only for the Al(III) and Cr(III) complexes, both under isothermal and programmed-temperature conditions; better resolution was observed on the column coated with OV 17.     

Study of Injection Angle and Carrier Gas Flow Rate Effects on Particles In-Flight Characteristics in Plasma Spray Process: Modeling and Experiments

This paper investigates the influence of particle injection angle on particle in-flight behaviors and characteristics at different primary and carrier gas flow rates through an integrated modeling and experimental approach. Particle in-flight status such as temperature, velocity, size and their distribution are analyzed to examine particle’s melting status before impact. Results from the experiments and numerical simulations both show that, when carrier gas flow rate is fixed, a small injection angle favors the particle melting and flattening. This behavior is independent of primary and secondary gas flow rates, spray distance and carrier gas flow rate. When both carrier gas flow and injection angle vary, a high carrier gas flow rate and a small injection angle are recommended for high particle temperature and velocity.     

Design,Development and Testing of Miniature Liquid-liquid Extraction Contactors for R&D Studies in Nuclear Environment

Testing liquid-liquid extraction flowsheets on radioactive solutions at laboratory scale requires specific contactors, that must be as small as possible (to minimize the quantities of reagents) and suitable for use in glove boxes or hot cells. As such contactors are not commercially available, CEA designs dedicated apparatus for its experiments. Two examples of such contactors are highlighted: a stage-wise one (a miniature mixer-settler) and a differential one (the Taylor-Couette column). Both combine similarities with larger contactors that make possible flowsheet extrapolation to industrial scale, and specific features, mainly because of the major role of materials wettability when volumes are reduced.     

氨基功能化金属有机骨架光催化剂的制备及性能研究

氨基功能化金属有机骨架材料(Metal-organic frameworks,MOFs)是一种非常具有吸引力的功能化MOFs,其兼具MOFs的高比表面积、孔道易调控及氨基的可后处理修饰的性能。通过简单的化学反应可实现功能基团的转化,从而制得新型的功能化MOFs,在气体存储、药物载体、选择性吸附气体小分子和催化等领域具有潜在的应用价值,因此开发氨基功能化的MOFs备受人们关注。本文综述了近年来氨基功能化MOFs在催化和吸附领域的研究进展,包括氨基功能化MOFs的制备方法、影响因素以及在环境方面的应用,并对今后的发展前景进行了展望。     

Influence of carrier gas on the prediction of gas chromatographic retention times based on thermodynamic parameters

We present an investigation into the influence of carrier gas on the thermodynamics governing a capillary gas chromatographic separation. Thermodynamic parameters are estimated for a series of alkanes and alcohols on three common stationary phases using helium, hydrogen, and nitrogen carrier gases. It is shown that the substitution of carrier gases for one another results in a change in the thermodynamic parameters governing the separation. The effect of the carrier gas on the thermodynamic parameters is large enough to compromise the accuracy of the retention time calculations based on thermodynamic parameters collected in a carrier gas other than the one actually in use in a specific gas chromatographic system. A possible kinetic explanation for these observations is also investigated.     

Computer comparisons of variables in capillary gas chromatography

A series of computer-constructed van Deemter curves that permits evaluation of a number of variables in capillary gas chromatography is presented. The graphs permit the comparison of inter-related parameters, including the choice of carrier gas (hydrogen vs helium vs nitrogen), column length (10-100 m), column diameter (0.20, 0.25, 0.32, 0.4 mm), solute partition ratios (0-10), and liquid phase film thickness (0.1, 0.25, 0.5, 1.0 μm). The curves are evaluated, both in terms of the relative magnitude of the optimum average linear carrier gas velocity, and in terms of the significance of the sharpness of the curve.     

The combination of gas chromatography-olfactometry and multidimensional gas chromatography for the characterisation of essential oils

A research area of great interest to the flavour industry is the analysis of odour active compounds in essential oils. In this paper, a methodology is presented for the identification of character-impact odorants in essential oil samples using (a) gas chromatography-olfactometry (GC-O); (b) comprehensive two-dimensional gas chromatography (GC x GC) combined to time-of-flight mass spectrometry (TOFMS) and (c) heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The specific advantages and limitations of each technique are discussed. The advantage of combining these techniques in a strategy to identify character-impact odorants is demonstrated using examples from coriander leaf (Coriandrum sativum) and hop (Humulus lupulus) essential oils. In particular, resolution of co-eluting regions of compounds and evaluation of their individual odour activity is discussed. In coriander leaf, only E-2-dodecenal was found to contribute to a co-eluting odour region, E-2-dodecen-1-ol and 1-dodecanol being present below detection threshold. Using MDGC on a hop essential oil sample, eight significant peaks were resolved from an 18 s heart-cut where a potent odorant was perceived during GC-O.     

Alltech集束毛细管柱和常规毛细管柱的比较

对集束毛细管气相色谱柱的色谱性能,如流速对柱效的影响、柱温对柱效的影响、柱容量等进行了考察,并将其对典型火炸药成分ＤＮＴ,ＴＮＴ的分离与常规毛细管气相色谱柱进行了比较。结果表明,集束毛细管气相色谱柱综合了填充柱与石英毛细管气相色谱柱之优点,弥补了二者的不足,是一种柱容量较大且分离效能好、可以在高载气流速下操作的新型气相色谱柱。     

乙烯基吡咯烷酮与二乙烯基苯原位共聚有机多孔高聚物毛细管柱的制备与性能

以乙烯基吡咯烷酮为单体，二乙烯基本为交联剂原位聚会制备出有机多孔高聚物OPPLOT－R型毛细管柱，对柱子的色谱性能进行了评价，考察了水以及载气中的O2，乙烯基吡咯烷酮含量的变化等对柱性能的影响，并对柱子的分离机理进行了初步探讨，最后给出了一些分析的实例。     

Mass Transport of β-Diketonate Precursors for MOCVD of YBa_2Cu_3O_(7-δ) High T_c Superconducting Thin Films

IntroductionSoonafterthediscoveryofhighT.supercoducting(HTSC)oxides,metalor-ganicchemicalvapourdeposition(MOCVD)wasproposedforpreparingtheirthinfilms[1j.Asgenerallyacceptedtoday['J,thistechniquehasdemonstrateditssuperioradvantagesinmakinglargeareahighqualityHTSCthinfilmsandwillplayamajorroleintheadvanceofdeviceapplicationofHTSCthinfilmsoverthenextfewyears.TheprecursorsusedinMOCVDforpreparinghighT.superconductingthinfilmsaremostlymetalbeta-diketonates.Theyaresolidsatroomtemperatureand…     

In situ infrared spectroscopy at electrochemical interfaces

An insight into the in situ FTIR spectroscopy method as applied in Electrochemistry is given. The particular aspects inherent to the electrochemical method are described in a concise form. Selected examples cover the results of about the last 8 years, on a variety of systems including carbon monoxide, small organic molecules and double-layer components (hydrogen, anions and water). The experimental data refer mostly to adsorption on well-defined single-crystal surfaces. Analogies and differences with data from the metal/gas interface are discussed.     

A new configuration for coupling purge-and-trap/cryogenic focusing/capillary column gas chromatography with splitless injection mode

A new configuration for coupling a purge-and-trap unit to a capillary column gas chromatograph via a cryogenic focusing interface has been developed. In this configuration, the precolumn of the cryogenic focusing interface was inserted through the septum of a split/splitless injection port where it served as both sample transfer and carrier gas supply lines. The injection port of the gas chromatograph was modified by plugging the carrier gas and the septum purge lines. This configuration allowed for the desorption of analytes at high flow rates while maintaining low, analytical-column flow rates which are necessary for optimum capillary column operation. The capillary column flow rate is still controlled by the column backpressure regulator. Chromatograms of purgeable aromatics exhibited improved resolution, especially for early eluting components compared to those obtained by direct liquid injection using the normal splitless injection mode. Quantitative sample transfer to the analytical column afforded excellent linearity and reproducibility of compounds studied.     

胺功能化配体多孔配位聚合物材料的碳捕捉和封存研究进展

近十年,多孔配位聚合物(porous coordination polymers, PCPs)因其晶体结构中可调节的孔道尺寸、形状以及化学功能化,在小分子的选择性吸附及分离领域受到了极大的关注。基于环境问题的严峻性,胺功能化PCPs材料对煤电厂燃烧废气中CO2优异的选择性吸附性能,使其在该领域拥有较好的应用潜力。本文综述了含末端氨基配体的PCPs材料应用于二氧化碳捕捉及存储的代表性工作,并对所存在的问题及发展方向进行了分析总结。     

Performance characteristics of a new prototype for a portable GC using ambient air as carrier gas for on-site analysis

The performance characteristics of a portable GC instrument requiring no compressed gas supplies and using relatively lightweight transportable components for the analysis of volatile organic components in large-volume air samples are described. To avoid the need for compressed gas tanks, ambient air is used as the carrier gas, and a vacuum pump is used to pull the carrier gas and injected samples through the wall-coated capillary column and a photoionization detector (PID). At-column heating is used eliminating the need for a conventional oven. The fused silica column is wrapped with heater wire and sensor wire so that heating is provided directly at the column. A PID is used since it requires no external gas supplies and has high sensitivity for many compounds of interest in environmental air monitoring. In order to achieve detection limits in the ppb range, an online multibed preconcentrator containing beds of graphitized carbons and carbon molecular sieves is used. After sample collection, the flow direction through the preconcentrator is reversed, and the sample is thermally desorbed directly into the column. Decomposition of sensitive compounds during desorption is greater with air as the carrier gas than with hydrogen.     

Theory of fast capillary gas chromatography part. 2: Speed of analysis

Using hold-up time as a measure of the speed of analysis with a given column efficiency, a theory of pneumatic optimization of a column in the fast high pressure drop isothermal and temperature programmed GC is developed. Expression for the hold-up time as a function of column efficiency, carrier gas velocity and film thickness is derived. Also found are the expressions for the minimum hold-up time and optimum gas velocity in a speed-optimized column. These quantities are compared with their counterparts in the efficiency-optimized column.     

A study of the oxidation of vegetable oils by inverse gas chromatography

Summary Inverse gas chromatography is shown to be suitable for the study of the oxidation of vegetable oils. With air as carrier gas characteristic plots of retention index versus time are obtained for hydroxylic test solutes that are consistent with the oxidation behaviour of vegetable oils. Shifts of retention are found to be accompanied by changes of column efficiency due to the oxidative crosslinking of polyunsaturated vegetable oils. The technique also leads to useful information concerning the oxidation of antioxidant inhibited systems. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984