The influence of the carrier gas on retention in capillary gas-solid chromatography

In capillary gas-solid chromatography where interactions between solute and carrier gas and adsorption of the solute on the surface of the adsorbent are considered to be imperfect, it has been shown that chromatographic retention is determined largely by adsorption processes. It has been established that correlation relationships k(P₂)=A k(P₁) + B, where k is the retention factor, and A and B are equation constants, was valid for use of different carrier gases P₁ and P₂. Column efficiency could be improved by use of carbon dioxide. The advantages of using carbon dioxide as the carrier gas were investigated.     

Investigation of the role of the carrier gas in capillary gas-solid chromatography

Nonideal interactions of the sorbate and the carrier gas and adsorption of the sorbate on the adsorbent surface in capillary gas-solid chromatography were studied. Chromatographic retention was found to be largely determined by adsorption processes. With respect to the retention coefficients (capacity factors) of a sorbate (k) with different carrier gases (P₁ and P₂), the correlation relationshipk(P₂) =A·k(P₁) +B (A, B are parameters of the equation) is closely obeyed. The advantages of carbon dioxide as the carrier gas were analyzed; the use of carbon dioxide allows the efficiency of the column to be enhanced.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 627–633, March, 1996.     

Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997.     

Influence of the carrier gas on retention factors of gaseous hydrocarbons on polytrimethylsilylpropyne using capillary gas chromatography

The retention factor and height equivalent of a theoretical plate for gaseous hydrocarbons C₁—C₄ were studied on capillary columns with the layer of the new polymeric adsorbent polytrimethylsilylpropyne (PTMSP) as functions of the nature and pressure of the carrier gas. The retention factor k increases in the series helium < nitrogen < carbon dioxide. The k values depend linearly on the average pressure of the carrier gas in a capillary column with the adsorption PTMSP layer.     

Solubility of some carrier gases in stationary liquid phases used in gas-liquid chromatography

A simple gas chromatographic technique for the determination of the solubility of gases in low-volatile liquids was proposed. The procedure is based on the introduction of a certain volume of the liquid saturated with the gas at atmospheric pressure into a gas chromatograph. The solubility of carrier gases (helium, hydrogen, nitrogen, methane, and carbon dioxide) in various stationary liquid phases (SLP), such as pentadecane, polydimethylsiloxane PMS-100, and polyethylene glycol PEG-600, was studied. The carrier gases studied can be arranged in the following series by solubility in SLP: He<H₂<N₂<CH₄<CO₂. This order coincides with the series reflecting change in the retention values in GLC for different carrier gases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 923–925, May, 1999.     

Ammonia as a carrier gas for acidic-basic chromatography

The influence of ammonia as a basic carrier gas on the retention of acidic and basic solutes was experimentally studied. Use of the basic carrier gas (ammonia) leads to an increase in retention of acidic solutes. A simplified theory on the influence of carrier gas basicity influence on the retention of acidic and basic solutes was developed. Contact of an inert gas with ammonia water at ambient temperature can be used to obtain basic humid carrier gas and to improve the chromatographic characteristics of amine's zones.     

Influence of a water vapor admixture in the carrier gas on capacity coefficients of polar organic compounds

The influence of a water vapor admixture in helium, nitrogen, and carbon dioxide on capacity coefficients of C₃−C₅ alcohols and pyridine during chromatography process in capillary columns with polar (PEG-20M) and nonpolar (SE-30) stationary phases was studied. The introduction of a water admixture into the carrier gas, increases the capacity coefficient of polar organic compounds on the capillary column with PEG-20M and has almost no effect on this value in the case of SE-30. The change in retention of polar organic compounds on the capillary column with the PEG-20M polar phase occurs due to a change in the properties of the stationary phase when it adsorbs water from the mobile phase. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2258–2261, November, 1998.     

Trapping Efficiencies of Various Adsorbents in Supercritical Fluid Extraction with Modified Carbon Dioxide

One way of collecting extracted analytes after a supercritical fluid extraction (SFE) is to pass the depressurized fluid through a trap composed of a solid adsorbent. The influence of the adsorbent nature on the trap efficiency has been studied. First, the retention factors of each compound of a polarity test mix (tetracosane, naphthalene, fluoranthene, acetophenone, N,N-dimethylaniline, 2-naphthol, decanoic acid) have been determined on five high specific area (greater than 800 m²/g) polymeric phases by supercritical fluid chromatography (SFC). The comparison of this values with those obtained on octadecyl silica (ODS) showed that polymeric phases have the greatest retention power. After that, the efficiency of a solid trap filled with the greatest retention power polymeric adsorbent was evaluated by using pure carbon dioxide and 2.5%, 5%, 10%, and 20% methanol-modified carbon dioxide. As expected, this trap permitted a quantitative collection of all the former compounds even when a content as high as 10% of methanol was implemented. A solid trap filled with ODS adsorbent allowed quantitative collection of all the compounds only at a methanol content lower than 2.5%.     

重量法测定灰岩中的二氧化碳

采用重量法对灰岩中的二氧化碳进行测定。首先用酸分解试样,在载气作用下,产生的二氧化碳被吸收液完全吸收,最后用重量法间接求出二氧化碳的含量。实验结果准确度高,矿石中的硫不干扰测定,可测定0.1%以上的二氧化碳。不经过复杂的气体净化步骤,操作准确、简单、易行,可用于灰岩中二氧化碳的测定。     

Continuous determination of carbon dioxide evolved during thermal decomposition reactions

A simple device suitable for continuous monitoring of carbon dioxide evolved during thermal decomposition reactions is described. Carbon dioxide is transported by a carrier gas through the device connected to thermoanalytical equipment and absorbed by soda lime reagent. The reaction heat released is linearly proportional to the amount of carbon dioxide absorbed.     

Reversed-Phase High Performance Liquid Chromatography of Carbon Dioxide

Abstract

An investigation of the qualitative aspects of the liquid chromatography of carbon dioxide is described. It is demonstrated that although injected as a high pressure liquid, carbon dioxide dissolves in aqueous methanol mobile phases and elutes as a solution. The detector response is discussed in terms of the possible chemical interactions between the carbon dioxide molecule and the mobile phase; the effect of eluent pH upon the response is described. The variation of relative retention with mobile phase composition is detailed and the results discussed in terms of Horvath's solvophobic theory.     

CO2 production from degraded woods via a novel integrated pyrolysis-combustion process

The process of combustion produces minimal amounts of CO₂ for conventional radiocarbon dating, making it difficult to estimate the age of the archaeological wood. Thus, the objective of this paper is to introduce a novel integrated pyrolysis-combustion process that will maximize the production of CO₂. Degraded wood samples were assumed to be archaeological samples for this study, namely Karas (Aquilaria malaccensis), Meranti (Shorea acuminate) and Setumpol (Hydnocarpus spp.) were used for this process. The process of CO₂ production was optimized by the application of design of experiment (DOE) and response surface method. The mathematical model was examined using the analysis of variance (ANOVA) at 5% level of significance. The temperature during the pyrolysis process, retention time and flow rates for the carrier gas (argon) were found to have a positive influence on the production of CO₂. A second-order model was obtained to predict the production of CO₂ as a function of temperature, retention time and flow rate. Optimum conditions for the production of CO₂ were obtained at a pyrolysis temperature of 300 °C, 20 min retention and 980, 984 and 987.6 ml/min argon flow rate for Karas, Meranti and Setumpol, respectively. The optimized yields of carbon dioxide produced were 82.57, 79.7 and 84% for Karas, Meranti and Setumpol, respectively. The different yields of carbon dioxide were due to the carbon content in the individual samples.     

Carbon dioxide separation from hydrogen and nitrogen by fixed facilitated transport in swollen chitosan membranes

The separation of carbon dioxide from hydrogen and nitrogen at high temperatures would be valuable to fuel cell, flue gas purification, and ammonia processes. A feed gas mixture of carbon dioxide, hydrogen and nitrogen (10% CO₂, 10% H₂, and 80% N₂) was used to evaluate water-swollen chitosan as a facilitated transport membrane for these applications. The amino group of the chitosan repeating unit could be the fixed carrier that facilitates carbon dioxide transport in the presence of water.     

Cationic Zinc Hydride Catalyzed Carbon Dioxide Reduction to Formate: Deciphering Elementary Reactions,Isolation of Intermediates,and Computational Investigations

Zinc has been an element of choice for carbon dioxide reduction in recent years. Zinc compounds have been showcased as catalysts for carbon dioxide hydrosilylation and hydroboration. The extent of carbon dioxide reduction can depend on various factors, including electrophilicity at the zinc center and the denticity of the ancillary ligands. In a few cases, the addition of Lewis acids to zinc hydride catalysts markedly influences carbon dioxide reduction. These factors have been investigated by exploring elementary reactions of carbon dioxide hydrosilylation and hydroboration by using cationic zinc hydrides bearing tetradentate tris[2-(dimethylamino)ethyl]amine and tridentate N,N,N′,N′′,N′′-pentamethyldiethylenetriamine in the presence of triphenylborane and tris(pentafluorophenyl)borane.     

Capillary electrochromatography using columns packed with a supercritical fluid carrier

Summary Columns for capillary electrochromatography may be prepared by packing reversed phase silica-based material using a supercritical fluid carbon dioxide carrier. Procedures for the in-situ manufacture of frits and UV detection windows, and the wetting of columns are described. The columns were employed in two commercial instruments (and a home-built system), and their properties investigated during the separation of standard mixtures of test compounds. The columns are highly efficient and durable, with reduced plate heights of 1.0–1.4. The repeatability of retention time, peak area and peak height was measured. The influence of applied voltage and column temperature and of electrokinetic injection parameters was explored, along with other practical considerations.     

Bimetallic systems containing Fe, Co, Ni, and Mn nanoparticles as catalysts for the hydrogenation of carbon oxides

The hydrogenation reaction of carbon dioxide and a mixture of carbon oxides on bimetallic catalytic systems containing nanoparticles of Fe, Ni, Co, and Mn supported on an inert carrier is studied. It is found that the ratio of saturated and unsaturated hydrocarbons in the hydrogenation products and the synergistic effect are determined mainly by the number of hydrogen atoms that are capable of migrating from one active center to another and by composition of those centers. Differences in the catalytic activity and selectivity of the bimetallic samples are explained by different rates of the spillover of weakly bound hydrogen (H_I) and the different rates of the jumpover of CH _x radicals from one center to another at which their further hydrogenation takes place.     

Carbon dioxide versus xenon as a mobile phase for flow cell packed column SFC/FT-IR

Xenon is compared to carbon dioxide as a mobile phase for super critical fluid chromatography/Fourier transform infrared spectrometry. The study showed xenon to be comparable to carbon dioxide in terms of resulting chromatography for non-polar analytes. Xenon was confirmed to be a very poor mobile phase, however, for polar analytes. It was determined that small wavenumber shifts in the infrared spectra of probe analytes occurred as either the density or temperature of the mobile phase was increased. The degree of these shifts was often similar for xenon and carbon dioxide. Analyte spectra for five different compounds were produced in both super critical xenon and carbon dioxide and compared to condensed phase and vapor phase library spectra. In all cases, carbon dioxide spectra were readily matched to their corresponding vapor phase spectra, despite having blanked portions of the spectrum due to carbon dioxide infrared absorption. Xenon produced technically superior spectra without such blanked regions, but at a much higher economical cost than carbon dioxide and with no real improvement in terms of library matching.     

固载Ru基催化剂上二氧化碳加氢合成甲酸的研究(IV): 反应机理

探讨了在CO₂加H₂合成HCOOH过程中原位合成的固载Ru基催化剂的可能结构、CO₂的活化方式以及可能的反应机理. 在反应中, 固载Ru配合物中的一个P配体首先解离, 被质子型溶剂ROH取代而生成循环活性物质, 然后CO₂正插入Ru—H键生成甲酸酯配合物, 之后甲酸酯配合物中的Ru—O₂CH键被H₂氢解生成HCOOH, 而本身重新转化为活性物质, 完成催化循环.     

Comparison of different packing methods for capillary electrochromatography columns

A study was carried out in which 50 microm I.D. fused-silica capillaries were packed with 3 microm octadecylsilane bonded silica, from the same batch, by four methods; liquid slurry and carbon dioxide supercritical carrier, each with and without the use of an ultrasonic probe. A neutral test mixture was analysed by capillary column in reversed-phase mode, and the reproducibility of the electroosmotic flow and of migration time, column efficiency and retention factors, was determined. Initially results suggested that there was no significant difference between properties of columns packed by different methods, and a more thorough statistical evaluation confirmed this; differences observed in the column performance were attributed to random variations between replicate columns, and not between packing methods. However, the variation was least when applying the ultrasonication during liquid slurry.     

Supercritical fluid extraction of oxindole alkaloids from Uncaria tormentosa

Supercritical fluid extraction of oxindole alkaloids from Uncaria Tormentosa is described. The extraction was performed with supercritical carbon dioxide alone and with supercritical carbon dioxide modified with 10% metanol, and the extracts were analyzed by GC/MS and HPLC/MS.