Gas chromatography separation techniques

Star anise volatile oils can also be isolated by supercritical C02 extraction coupled to a fractional separation technique. Gas chromatography-mass spectrometry analysis of the various fractions obtained in different extraction and fractionation conditions allowed the identification of the best operating conditions for the isolation of essential oil. A good extraction performance was obtained operating at 90 bar and 50°C (for 630min) for both treated materials. Optimum fractionation was achieved in both cases by operating at 90 bar and -10°C in the first separator and at 15 bar and 10°C in the second (Della Porta eta/., 1998). 

In order to analyse a complex mixture, for example natural products, a separation technique - gas chromatography (GC), liquid chromatography (LC) or capillary electrophoresis (CE) - is coupled with the mass spectrometer. The separated products must be introduced one after the other into the spectrometer, either in the gaseous state for GC/MS or in solution for LC/MS and CE/MS. This can occur in two ways the eluting compound is collected and analysed off-line or the chromatograph is connected directly to the mass spectrometer and the mass spectra are acquired while the compounds of the mixture are eluted. The latter method operates on-line. Reviews on the coupling of separation techniques with mass spectrometry have been published in the last few years [1-4]. 

Solid-phase extraction (SPE) has been used in conjunction with separation techniques [gas chromatography (GC), liquid chromatography (LC), and capillary electrophoresis (CE)] for environmental analysis. Recent developments in both SPE and solid-phase microextraction (SPME) have been reviewed. Some of the solid phases investigated previously include graphitized carbon black, octadecylsilica, and Ci8 cartridges. Comparisons of the sorbent materials available for the extraction of phenols have been carried out in conjunction with chromatographic separations. A comparison of polycrystalline graphites and SPME fibers [poly (dimethyl... 

The analysis of pollutants in environmental samples is complicated by the fact that these compounds are often part of a very complex mixture of hundreds of chemicals and that they are present at extremely low concentrations. Thus, any instrumental technique that is to be used successfully in environmental analysis should allow the separation of such complex mixtures and the identification of the constituents at trace level. Mass spectrometry (MS) is particularly suited for this purpose as it can be coupled with the most important instrumental separation techniques - gas chromatography (GC) and liquid chromatography (LC) - while at the same time it is one of the most sensitive instrumental methods available for the analysis of contaminants. Moreovei it is not only the sensitivity, but also the specificity that makes MS the most powerful instrumental method in environmental analysis. 

Separation techniques gas chromatography (GC), and high-performance liquid... 

The combination of chromatography and mass spectrometry (MS) is a subject that has attracted much interest over the last forty years or so. The combination of gas chromatography (GC) with mass spectrometry (GC-MS) was first reported in 1958 and made available commercially in 1967. Since then, it has become increasingly utilized and is probably the most widely used hyphenated or tandem technique, as such combinations are often known. The acceptance of GC-MS as a routine technique has in no small part been due to the fact that interfaces have been available for both packed and capillary columns which allow the vast majority of compounds amenable to separation by gas chromatography to be transferred efficiently to the mass spectrometer. Compounds amenable to analysis by GC need to be both volatile, at the temperatures used to achieve separation, and thermally stable, i.e. the same requirements needed to produce mass spectra from an analyte using either electron (El) or chemical ionization (Cl) (see Chapter 3). In simple terms, therefore, virtually all compounds that pass through a GC column can be ionized and the full analytical capabilities of the mass spectrometer utilized. 

Characterization of various types of damage to DNA by oxygen-derived species can be achieved by the technique of gas chromatography-mass spectrometry (GC-MS), which may be applied to DNA itself or to DNA-protein complexes such as chromatin (Dizdaroglu, 1991). For GC-MS, the DNA or chromatin is hydrolysed (usually by heating with formic acid) and the products are converted to volatile derivatives, which are separated by gas chromatography and conclusively identified by the structural evidence provided by a mass spectrometer. Stable isotope-labelled bases may be used as internal standards... 

A number of techniques have been used for the speciation of arsenic compounds. The most important has been the formation of volatile hydrides of several species, separation by gas chromatography and detection by AAS. HPLC has been used to separate arsenic species. Several types of detectors have been studied for the determination of arsenic species in the column effluent. These have included AAS both off- and on-line, ICPAES and ICP-MS. An important comparative study of coupled chromatography-atomic spectrometry methods for the determination of arsenic was published (Ebdon et al., 1988). Both GC and HPLC were used as separative methods, and the detectors were FAAS, flame atomic fluorescence spectrometry (FAFS) and ICPAES. The conclusions were (1) that hydride generation and cryogenic trapping with GC-FAAS was the most... 

The new technique, gas chromatography or GC, was found to be simple and fast and capable of producing separations of volatile materials that were impossible by distillation. Furthermore, the theories were found to be rather accurate in predicting optimal operating conditions, and the theories could be quickly tested. The field exploded New separations led to new ideas to be tested and vice versa. GC quickly matured. 

The isolation of atropine, scopolamine, and cocaine occurred long before the development of modern analytical techniques. Gas chromatography was the first instrumental technique available in the field of separation science and thus it is not surprising that these alkaloids were firstly analyzed by GC despite their low volatility. With the advent of capillary columns and the proliferation of various sample introduction and detection methods, GC has evolved as the dominant analytical technique for screening, identification, and quantitation of tropane alkaloids of plant origin as well as in biological fluids. The state-of-the-art of GC analysis of tropane alkaloids has been the subject of two comprehensive reviews [45,58]. We shall therefore mainly focus on publications which have appeared since 2002. 

Separated by Gas Chromatography, using a Potassium Bromide Micro-pellet Technique, Z. Anal, Chem. (1969) 246, 294-297. 

Gas chromatography/mass spectrometry was a different story. Because molecules that had been separated by gas chromatography were already in the gas phase, they could be readily ionized and manipulated. Well into its 5th decade, gas chromatography continues to be a successful analytical technique, especially in environmental science. The difficulty with gas chromatography was that it only worked for a minor ( 20) percentage of the molecules of interest [7], and it worked better for nonionic molecules than for ionic molecules. Because of this, gas chromatography has been of limited utility in pharmaceutical science, where the majority of drugs and metabolites are polar or ionic. 

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