Study of the Selectivity of Binary Agents by Gas–Liquid Chromatography

Theoretical Foundations of Chemical Engineering - The selective properties of individual and binary agents are compared according to data obtained by gas–liquid chromatography (GLC). The...     

The Choice of Selective Agents for Extractive Distillation by Gas–Liquid Chromatography

Data on the selectivity in the case of infinite dilution obtained using gas–liquid chromatography have been analyzed for seven industrial separating agents. Selective agents for the extractive distillation of binary systems of various types have been recommended.     

Analysis of Cyanolipids from Sapindaceae Seed Oils by Gas Chromatography–EI-Mass Spectrometry

As a continuation of our investigation on unusual lipids, in the present work we describe a method based on GC–FID and GC–EI-MS to analyze the molecular composition of intact cyanolipids (CL) from selected Sapindaceae plants. We applied our method to the study of CL of type I (1-cyano-2-hydroxymethyl-prop-2-en-1-ol-diester) from Paullinia cupana var. sorbilis and Allophylus dregeanus and CL type III (1-cyano-2-hydroxymethyl-prop-1-en-3-ol-diester) from A. natalensis and Nephelium lappaceum. Our analytical approach allowed us to obtain useful mass spectra to identify individual isomeric molecular species composing the CL mixtures and resulted in the very sensitive detection and identification of minor CL. Defined CL mass spectra resulted in suitable detection of these phytochemicals in complex plant oil mixtures containing acylglycerols. To the best of our knowledge GC–EI-MS spectra of cyanolipids have never been reported before. Moreover, this study improved previous knowledge of the lipid chemistry of Sapindaceae plants.     

Characterization of the Organic Matter of Humic Acids by Pyrolytic Gas Chromatography–Mass Spectrometry

The results of the pyrolytic analysis of products of the organic matter of Sphagnum fuscum, fuscum peat, and humic acids separated from peat with the use of pyrolysis–chromatography–mass spectrometry in the Rock-Eval version are presented. It was shown that Sphagnum fuscum and peat differed only slightly in the degrees of chemical transformation. Benzene, phenol, and their alkyl-substituted homologues predominated in the thermal desorption products of humic acids upon pyrolysis to 400°C. Acetic acid, monohydric phenols, syringol, and guaiacol, which are the basic compounds in the high-temperature fraction, were formed on the pyrolysis humic acids to 700°C from the carbohydrate, phenylpropionic, and guaiacylpropane structural fragments.     

Identification of Host and Nonhost Semiochemicals of Eucalyptus Woodborer Phoracantha semipunctata by Gas Chromatography–Electroantennography

The host range of the eucalyptus woodborer, Phoracantha semipunctata, is restricted mainly to species of Eucalyptus (Myrtaceae). Volatile semiochemicals possibly involved in host selection and nonhost rejection were identified by high-resolution gas chromatography–electroantennography on samples obtained by air entrainment of foliage from host and nonhost trees. Compounds from the main host E. globulus, active at physiologically significant levels, included 3-hydroxy-2-butanone, 3-methyl1-butanol, a branched epoxyalkane, ethyl 3-methylbutanoate, (Z)-3-hexen1-ol, -pinene, -pinene, p-cymene, 1,8-cineole, limonene, and guaiene. E. camaldulensis gave a similar spectrum of volatiles that also included -terpinene and linalool. The volatiles from E. tereticornis were similar to E. globulus but without ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, 1,8-cineole, or limonene. The nonhost Pinus pinaster (Pinaceae) yielded active compounds common to the host species, including ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, -pinene, -pinene, p-cymene, 1,8-cineole, limonene, and linalool but, in addition, myrcene, (E)--ocimene, and -cubebene as candidate nonhost cues. The nonhost Olea europeae (Oleaceae) also shared some active compounds in common with the host species, including 3-hydroxy-2-butanone, 3-methyl-1-butanol, the branched epoxyalkane, ethyl 3-methylbutanoate, (Z)-3-hexen-1-ol, -pinene, but an apparent nonhost cue from this species was the homomonoterpene (E)-4,8-dimethylnona-1,3,7triene, plus other compounds so far unidentified.     

Organic Vapor/Gas Mixture Separation by Membrane–-A Parametric Study

Abstract

A parametric study was carried out for the membrane separation of organic vapor-gas mixtures. Based on a set of basic transport equations, the effect of the concentration polarization on the membrane surface as a function of mass transfer coefficient is illustrated. It is shown that the concentration polarization is negligible for membranes of low permeability but would be significant for highly permeable and selective membranes. The effects of some operating parameters and membrane permselectivity on the separation performance are also discussed. The results demonstrate the utility of parametric analyses for exploring the effects of variations in the membrane separation of organic vapor-gas mixtures.     

Combustion of Solid‐Propellant Charges with Highly Progressive Gas Release

The problem of the burning of structural configurations ensuring highly progressive gasrelease is solved. Cylindrical, mushroomlike, and toroidal configurations are considered. Solutions are obtained in the form of quadratures or elementary functions. It is shown that in all the cases considered, not only the first but also the second derivative of the burning surface as functions of the amount of the burnt vault are positive. The increase in burning surface as a function of the length of the burnt vault is nonlinear in all cases, and it can be more rapid than a quadratic parabola (for spiral cylindrical and mushroomlike charges).     

Explosive Hazard of Vapor–Gas Mixtures of Fluoride‐Containing Saturated Hydrocarbons with Fluoride and Chlorine Trifluoride

The limits of explosion of the CF₃CFH₂–F₂–N₂, C₃F₈–F₂–N₂, C₄F₈–F₂–N₂, C₄F₈–ClF₃–N₂, C₄F₁₀–ClF₃–N₂, and F₂ClCF₂Cl–F₂–N₂ mixtures are determined. For some compositions of the first two mixtures, the maximum pressure of explosion and the maximum pressuregrowth rate are measured. The transition from deflagration to detonation is observed in undiluted mixtures close to stoichiometric compositions. The burning rates of the mixtures examined are comparable with the burning rates of oxygen–hydrogen mixtures.     

On-line Thermal Desorption–Gas Chromatography of Intact Insects for Pheromone Analysis

By using a thermodesorption system (TDS) together with a programmable temperature vaporizer (PTV) injector, we confirmed the composition of the sex pheromone of Adoxophyes orana (Lepidoptera: Tortricidae) and Campylomma verbasci (Heteroptera: Miridae) from a single insect per analysis. Intact females and males or pheromone glands were placed in the oven part of the TDS, which was subsequently heated. The compounds released were transferred to the PTV, which was cooled to –150°C. Injection was on a dual-column GC by heating the PTV rapidly to 250°C. The major sex pheromone compounds of A. orana were found only in the pheromone gland of females. Male and female C. verbasci showed fingerprint-identical chromatograms, except for the two sex pheromone compounds, which were present only in females. No distinct differences were found in compounds released from female and male Lygocoris pabulinus (Heteroptera: Miridae). The advantages of this rapid method are the high sensitivity and the low degree of degradation and contamination. This technique was effective in analyzing small insects by gas chromatography–mass spectrometry (GC-MS) without prior manipulation, such as solvent extraction or distillation.     

Mathematical Combustion Model of a Two–Component Gas Suspension Including a Powder Combustible and a Powder Oxidizer

A mathematical model of the ignition and combustion of aluminum and ammonium perchlorate powders in a propulsion system that takes into account their polydisperse distribution and the difference between the gas and disperse–phase velocities and temperatures is developed. The effect of the pressure, the ratios between the components, and the dispersivity of aluminum particles on the structure of a gas–disperse flame, the basic characteristics of the combustion of a gas suspension, and the completeness of propellant combustion is studied.     

Combination of TLC Blotting and Gas Chromatography–Mass Spectrometry for Analysis of Peroxidized Cholesterol

We have established a sensitive and convenient method for analysis of cholesterol hydroperoxides (Chol-OOHs) as trimethylsilyloxyl derivatives using diphenylpyrenylphosphine (DPPP)-thin-layer chromatography (TLC) blotting and gas chromatography–electron ionization–mass spectrometry/selected-ion monitoring (GC–EI–MS/SIM). Chol-OOH standards were prepared by photosensitized oxidation and azo radical-induced peroxidation of cholesterol. Trimethylsilyloxyl derivatives of cholesterol 5α-hydroperoxide (Chol 5α-OOH), cholesterol 7α-hydroperoxide (Chol 7α-OOH), and cholesterol 7β-hydroperoxide (Chol 7β-OOH) could be separated from one another in the SIM chromatogram using a fragment ion with elimination of trimethylsilanol from the molecular ion. This method was used to characterize peroxidized cholesterol from azo radical-exposed human low-density lipoprotein and UVA-irradiated human keratinocytes in the presence of hematoporphyrin. Finally, we succeeded in the quantification of each Chol-OOH isomer present in hairless mouse skin with and without UVA irradiation by use of β-sitosterol hydroperoxide as internal standard. The accumulation of Chol 5α-OOH with Chol 7α/βOOH in the skin indicates that singlet molecular oxygen (¹O₂) participated in the peroxidation of skin cholesterol, because Chol 5α-OOH is known to be a ¹O₂ specific cholesterol peroxidation product. We concluded that the combination of DPPP-TLC blotting and GC–EI–MS/SIM is useful for quantifying peroxidized cholesterol in biological samples and confirming the participation of ¹O₂ in oxidative stress.     

Gas‐Dynamic Method of Determining Combustion Efficiency in a Model with Combustion

A method of determining combustion efficiency and testgas parameters along the combustion chamber with a supersonic velocity of air at the entrance is considered. The composition and properties of the test gas are determined by a thermodynamic calculation with allowance for dissociation and temperature dependence of the energy of internal degrees of freedom. The sources of errors and the influence of accuracy of initial data definition in a zerodimensional approach to determining the combustion curve and flow parameters are studied.     

Separation of Binary Liquid Systems by Sorption—A Comparison with Pervaporation

Abstract

Studies were carried out on the separation of the ethanol-water and the methanol-acetone systems by sorption using different commercially available molecular sieves (m.s.) as adsorbents. The separation factor (α) is found to be around 100 for m.s. 3A/ethanol-water system and is around 85 for m.s. 4A/ methanol-acetone system at respective azeotropic compositions. These separation factors appear to be better than the results reported by many workers using membrane process “pervaporation.” A comparison is made between the selectivity of pervaporation and sorption with respect to the systems studied.     

Separation of Gas Mixtures by the Absorption–Pervaporation Method

Absorption–pervaporation separation of gas mixtures is studied and compared with membrane gas separation. The absorption–pervaporation method ensures a much higher separation coefficient of the HCl–H₂mixture. An equation is derived for calculating the fluxes of the mixture components through the absorbent–membrane system.     

Structural Study of Li–Fe–P–O Powder Synthesized by the Extraction-Pyrolytic Method

Theoretical Foundations of Chemical Engineering - Iron lithium phosphorus oxide, which is promising for use as a cathode material in lithium-ion batteries, has been synthesized by the...     

Calculation Studies of the Separation of Rare-Earth Metals by Countercurrent Liquid–Liquid Chromatography

Theoretical Foundations of Chemical Engineering - Calculation studies have been made of the separation and concentration of rare-earth metals by countercurrent liquid–liquid chromatography...     

Deuterium Tracer Studies and Gas Chromatography–Mass Spectrometry Analysis of Deuterated Products during Fischer–Tropsch Synthesis

Hydrogen is one of the two reagents of Fischer–Tropsch (FT) synthesis. In order to have the information about the role of hydrogen, which is the key to understand the mechanism of the reaction, deuterium tracer experiments are useful. One of the obstacles in conducting deuterium tracer experiments during FT reactions is to accurately determine the amounts of isotopomers of a hydrocarbon in the FT products. Because of an inverse isotope effect for isotopomers on a GC column, the isotopomer with more deuterium atoms will be eluted first. If the difference in deuterium atoms is >3, the quantitative analysis of a mixture of isotopomers can be conducted using GC–FID. However, if the difference in deuterium atoms is <3, an accurate measurement of the relative amounts of isotopomers of a compound requires a determination of the total area of all of the molecular ions by gas chromatography–mass spectrometry (GC–MS). The results determined using this method are close to the true value (by weight) with an error of ±3 %. The deuterium tracer technique and GC–MS analysis of FT products have been used to study the accumulation effects, the role of H₂O, the isotope effect, the role of C₂ species derived from ethanol and ethene, and deuterium enrichment during FT reactions.     

The Analysis of Dimethylphenanthrenes by Direct Deposition Gas Chromatography – Fourier Transform Infrared Spectroscopy (GC-FTIR)

Abstract

Dimethylphenanthrenes (DMPs) occur as complex mixtures in crude oils and sedimentary rock extracts. Conventionally these mixtures are analysed using gas chromatography-mass spectrometry (GC-MS) employing a column with a medium polarity stationary phase. Under these conditions, complete resolution of the mixture is not achieved and several isomers co-elute. Furthermore, the mass spectra of these co-eluting isomers may be so similar that one is unable to differentiate between them, and their abundance may therefore not be determined.

In this paper, we describe the application of GC-FTIR as a complementary technique to GC-MS in the analysis of three co-eluting DMP isomers. Since each isomer has a unique infrared spectrum, the proportion of each in the mixture was determined by comparing the spectrum of the co-eluting compounds with the spectrum of each of the isomers. The result of this analysis was confirmed by the use of mordenite molecular sieves to separate the mixture into simpler fractions, and subsequent analysis by GC-MS and GC-FTIR.     

Evaluation of Lysophospholipid Measurement in Cerebrospinal Fluid Samples using Liquid Chromatography–Tandem Mass Spectrometry

A quantification system for lysophospholipids (lysoPL) was developed, especially for blood samples, using liquid chromatography–tandem mass spectrometry (LC–MS/MS). However, the lysoPL measurement in cerebrospinal fluid (CSF) has not been validated. Therefore, the present study aimed to validate the lysoPL measurement using CSF samples and to elucidate the possible clinical significance of the lysoPL measurement in CSF. For the validation, we observed a good precision and linearity in a sample with high lysoPL levels. The concentrations of lysoPL changed after incubation but the changes were smaller than those observed for serum samples. Moreover, we observed that the CSF levels of 16:0, 18:0 lysophosphatidylcholine, and 18:0, 18:1, and 20:4 lysophosphatidic acid were significantly higher in subjects with central nervous system invasion caused by hematological malignancies or carcinoma than in subjects with no abnormal CSF test results. In conclusion, an LC–MS/MS quantification system for lysoPL in CSF might be useful and could be applied to clinical laboratory testing.