A comprehensive two-dimensional gas chromatography (GC x GC) instrument has been created by coupling a flow-switching modulator and a standard gas chromatograph. The instrument was used to characterize the aromatic composition of gasoline. The high-resolution separation produced by flow-switching GC x GC allowed gasoline aromatics to be fully resolved from saturated components. The aromatic compounds were further separated into groups having the same carbon number. A standard gasoline sample was analyzed to evaluate the quantitative accuracy and precision of this technique. The data show that flow-switching GC x GC produces results that are comparable to gas chromatography-mass spectrometry (GC-MS) and thermal modulation GC x GC. The simple, low-cost, and robust nature of flow-switching GC x GC makes it an ideal technique for the routine analysis of aromatic compounds in gasoline. 相似文献
A laser-based ionization source for the direct analysis of liquid samples in ion mobility (IM) spectrometry is presented and characterized. Ionization of aromatic substances in liquids is achieved, analogous to atmospheric pressure laser ionization (APLI) in mass spectrometry, by vaporizing the liquid and subsequently ionizing the aromatic substances by resonance-enhanced multiphoton ionization (REMPI). The effects of parameters, such as composition and flow rate of the solvent as well as laser wavelength and pulse energy, are systematically investigated. The characterization of the IM spectrometer is carried out by means of selected substances from diverse fields of applications, e.g., polycyclic aromatic hydrocarbons (PAH), pesticides, wood preservatives and drug compounds. Limits of detection (LOD) down to 10 fmol and linear ranges up to three orders of magnitude are established. In addition to direct laser ionization, indirect laser ionization via dopants (toluene) for substances with low ionization efficiencies is investigated. Ionization occurs as a result of proton transfer from toluene radical cations to substances of sufficiently high proton affinities. As a result of indirect laser ionization, LOD could be decreased by up to two orders of magnitude. Ionization products are investigated by means of a combination of IM and mass spectrometer. Depending on the substance investigated primary ions (radical cations) and secondary ions (protonated molecules) resulting from ion molecule reactions are formed. 相似文献
This paper describes a method for determining both the total sulfur content and the concentration of oxygenated additives in gasoline by gas chromatography with atomic emission detection (GC-AED). The AED provides selective detection of oxygen and sulfur compounds. Because the response factors for sulfur and oxygen are largely independent of the type of compound, calibration and determination of total element content are simplified. The use of a 0.1 mm i.d. capillary column enables complete elution of the components of the gasoline in under 10 minutes. 相似文献
Summary This work reports a rapid and easy procedure for the analysis of the aromatic fraction in gasoline. No sample pretreatment is required, since the gasoline is diluted in methanol and directly injected into a liquid chromatograph. A spectrophotometer detector and a spectrofluorimeter detector are used in series. The procedure has been applied to a large number of Italian and European refined gasoline samples.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday. 相似文献
Headspace solid-phase microextraction has been applied to the analysis of aroma compounds in vinegar. Silica fibre coated with Carboxen-polydimethylsiloxane was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, Carbowax-divinylbenzene, and polydimethylsiloxane-divinylbenzene, but its repeatability was low. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength, and sample volume were optimised using a two-level factorial design expanded further to a central composite design. This chemometric tool is very appropriate in screening experiments where the aim is to investigate several possibly influential and/or interacting factors. The extraction efficiency is inversely affected by the acetic acid content-an increase in the acetic acid concentration decreases the extraction efficiency. No interference is observed with the increase in content of polyphenols. 相似文献
The possibility of determining pyrene, anthracene, and fluorene in gasoline by phosphorimetry at room temperature after the
micellar extraction with sodium dodecyl sulfate was examined. It was found that the above polynuclear aromatic hydrocarbons
simultaneously present in gasoline can be selectively determined by room-temperature phosphorimetry using different techniques
for the excitation and population of the triplet states of luminophore (stationary and pulse excitation and triplet energy
transfer). The proposed procedure was verified by gas chromatography with a mass-selective detector. 相似文献
A new procedure has been developed for the quantitation of aromatic amines in mainstream cigarette smoke. Two solid-phase extraction (SPE) cleanup steps using different retention mechanisms are required to process the samples. The first step uses a cation-exchange cartridge, followed by a second step that uses a cartridge with a hydrophobic retention character. The aromatic amines eluted from the second SPE cartridge are derivatized with heptafluorobutyric anhydride and analyzed with GC-MS selected ion monitoring in the negative chemical ionization mode. This new method has several advantages over other reported techniques, being sensitive, robust, and easily automated. The detection limits ranged from 0.02 ng/cigarette for tolidine to 1.41 ng/cigarette for aniline and the recoveries were from 79 to 109%. 相似文献
A series of 36 compounds of known structure was used in a study to elucidate the mechanism of separation of gel-permeation chromatography (GPC). The various molecular dimensions were defined and measured for these compounds. The elution volume for these compounds was determined by GPC under specified and controlled conditions. The relationships between elution volume and molecular dimension were investigated using computer-based statistical analysis for the entire set of compounds and manual simultaneous equations for smaller sets of compounds. It was found that, as increasingly more molecular dimensions are considered, (1) the importance of the maximum molecular dimension Ap′ (the only dimension considered by many investigators) significantly decreases and (2) a significantly better prediction of the elution volume of these compounds could be made. 相似文献
Summary Coelectroosmotic capillary zone electrophoresis (CZE) has been investigated as a means of rapid analysis of twelve aromatic
sulphonate compounds. The main factors affecting reversal of electroosmotic flow (EOF)—type of osmotic modifier and concentration-were
studied. Two types of osmotic modifier, an alkylammonium salt (cetyltrimethylammonium bromide, CTAB) and a cationic polyelectrolyte
(hexadimentrine bromide, HDB) were investigated. The composition of the running buffers was optimized according to the characteristics
of each osmotic modifier. A concentration of HDB as low as 0.0001% (w/v) was used successfully to provide a stable and reversed EOF. 相似文献
The investigation of odorants is not an easy task, which needs to be undertaken in the context of fit-for-purpose quality systems. To date, great attention has been paid to determination of the volatile fractions of odorants, since they are responsible for the attributes of global flavor [i.e. a combination of olfactory (aroma) and gustatory (taste) sensations produced by chemicals]. This kind of determination can be carried out by analytical techniques [e.g., gas chromatography (GC) combined with mass spectrometry and/or olfactometric GC]. Methods complementary to GC analysis are available, allowing assessment of the olfactory impact by an electronic nose (e-nose) or a panel of selected individuals. Also, we consider some innovative analytical techniques to study the effects of odorants in food during consumption. 相似文献
Trifluoromethyl groups attached to aromatic compounds are usually prepared by perchlorinating a methyl group and is subsequently perfluorinated by halogen exchange using a fluorinating agent. In addition to this method, which is also used in industry, there are also a number of different synthesis methods which are however only of limited importance owing to the costly reagents required. The disadvantage of the above-mentioned two-step synthesis lies in the restricted range of application since many of the substituents attached to the aromatic compound hinder the chlorination of the methyl group or they are themselves changed (e. g. methyl, bromine …).By means of a new one-step process, the trifluoromethylation of aromatic compounds is made possible by using the reagent HF/CCl4. RH, alkyl, aryl, halogen, phenoxyThe anhydrous hydrofluoric acid acts as a Friedel-Crafts-catalyst, solvent and fluorinating agent. The fange of application of the reaction is discussed. Apart from indicating the influence of the concentration of the reaction components, temperature and pressure, details are also given concerning catalysts and side reactions. 相似文献
The reaction of β-ethoxyvinylpyrylium salts with aromatic compounds gives styrylpyrylium salts, which are also formed from methylpyrylium salts, ethyl orthoformate, and aromatic compounds. The previously unknown phenomenon of attack by a carbonium cation on the meta position of a benzene ring passivated by a nitro group (nitrobenzene) was detected. 相似文献
The review summarizes new data on the introduction of alkenyl (vinyl) groups into aromatic and heteroaromatic structures via reactions with alkenes and alkynes. The main attention is given to the characterization and estimation of synthetic potential of the alkenylation of aromatic compounds with acetylene derivatives in the presence of transition metal complexes, as well as by the action of electrophiles, Lewis acids, and Brønsted superacids. 相似文献