Gas chromatographic separation

A variable-size simplex optimization of a gas chromatographic separation using oven temperature and carrier gas flow rate as factors is described in this experiment. 

The first (inconclusive) work bearing on the synthesis of element 104 was published by the Dubna group in 1964. However, the crucial Dubna evidence (1969-70) for the production of element 104 by bombardment of 94PU with loNe came after the development of a sophisticated method for rapid in situ chlorination of the product atoms followed by their gas-chromatographic separation on an atom-by-atom basis. This was a heroic enterprise which combined cyclotron nuclear physics and chemical separations. As we have seen, the actinide series of elements ends with 103 Lr. The next element should be in Group 4 of the transition elements, i.e. a heavier congenor of Ti, Zr and Hf. As such it would be expected to have a chloride... 

This novel manifestation of the gas chromatographic separation demands that Our fundamental understanding of the GC method-invariably of single-dimensional scope-is challenged as follows concepts of column efficiency and separation are now Supplanted by a need to compare the performances of two columns operating... 

When John Phillips, in 1991, presented the practical possibility of acquiring a real comprehensive two-dimensional gas chromatographic separation (33), the analytical chemists in the oil industry were quick to pounce upon this technique. Venkatramani and Phillips (34) subsequently indicated that GC X GC is a very powerful technique, which offers a very high peak capacity, and is therefore eminently suitable for analysing complex oil samples. These authors were able to count over 10 000 peaks in a GC X GC chromatogram of a kerosine. Blomberg, Beens and co-workers... 

Gas chromatography/mass spectrometry (GC/MS) is the synergistic combination of two powerful analytic techniques. The gas chromatograph separates the components of a mixture in time, and the mass spectrometer provides information that aids in the structural identification of each component. The gas chromatograph, the mass spectrometer, and the interface linking these two instruments are described in this chapter. 

Figure 7. Infrared spectrum of pyrethrin I Isolated after dual partition chromatography First partition column. Celite-acetonitrile-hexane Second partition column. Silicic acid-nitromethane-hexane (with 5% acetone). Corresponds to peak 3 of gas chromatographic separation of pyrethrum mixture...

The gas chromatographic separation of some sulphoxide enantiomers was observed on quartz fused silica capillaries coated with the chiral silicon phase chirasil-val280. 

DeWild JF, Olson ML, Olund SD. 2002. Determination of methyl mercury by aqueous phase ethylation, followed by gas chromatographic separation with cold vapor atomic fluorescence detection, U.S. Geological Survey Open File Report 01 45, 23 p. 

TYPICAL HOMOCHIRAL DERIVATIZING REAGENTS FOR GAS CHROMATOGRAPHIC SEPARATION OF ENANTIOMERS... 

Cook WG, Ross RA. 1972. Gas-chromatographic separation of hydrogen sulfide, air, and water. Anal Chem 44 641-642. 

In some cases it is necessary unambiguously to identify selected components separated during gas chromatographic examination of oil spill material. Such methods are needed from the standpoint of the enforcement of pollution control laws. The coupling of a mass spectrometer to the separated components emerging from a gas chromatographic separation column enables such positive identifications to be made. 

The heptafluorobutyrate derivative was selected for gas chromatographic separation, using electron capture detector (ECD), in order to enable the detection of ultramicro quantities43. The interest in the analysis of natural and synthetic hormones in very small concentrations enhanced the development of the GC method, in comparison with the UV study.44... 

Figure 1-18. Gas chromatographic separation of a) synthetic racemic dihydromanicone rac- 44 b) natural 44, obtained by hydrogenation of material from the heads of M. rubida c) co-injected natural-44 and rac-44 d) synthetic (4 5,65 )-44 and e) co-injected synthetic (4RS,6S)-44 and rac-44. Chiral GC phase nickel(II)-bis[3-heptafluorobutyryl-(lR)-camphorate]. Signals 1 and 4 correspond to the pair of diastereomers (4 5,65)-44 signals 2 and 3 correspond to (4RS,6R)-44. Reprinted, with permission, by VCH, Ref. 63.

Recent advances in gas chromatographic separations of enantiomers allow precise determination of the enantiomeric purity of the algal pheromones. The czs-disubstituted cyclopentenes, such as multifidene, viridiene, and caudoxirene, are of high optical purity [ 95% enantiomeric excess (e.e.)] whenever they have been found (32,33). The situation is different with the cyclopropanes and the cycloheptadienes, as shown in Table 2 and Figure 1. Hormosirene from female gametes or thalli of... 

FIGURE 8 Gas chromatographic separation of the volatiles of D. diemensis egg extracts (47). Conditions fused silica column OV 1 (10 m X 0.32 mm) 50°C isotherm for 2 min, then at 10°C/min to 250°C injection port 250°C detector Finnigan ion trap, ITD 800 transfer line at 270°C electron impact (70 eV) scan range, 35-250 Da/sec. For identity of numbered compounds refer to Figure 9. 

MS requires that the components in the sample are driven into the gas phase. All gas chromatographic separations also require the sample components to be in the gaseous state. Thus, the two methods are compatible. It is possible, however, to do an MS analysis on samples without the MS being attached to a gas chromatograph (see Chapter 14). 

Procedures for determining fatty acids in sediments involved liquid-liquid extraction, liquid-solid adsorption chromatography followed by gas liquid chromatographic analysis [10-12], Liquid extractions have been performed with methanol-chloroform [13], methylene chloride [14] and benzene-methanol [15, 16]. Typical liquid-solid adsorbents are silicic acid. Standard gas chromatographic separations for complex mixtures employ non-polar columns packed with OV-1, OV-17, OV-101, SE-30, or glass capillary columns containing similar phases. 

Addison and Ackman [69] have described a direct determination of elementary yellow phosphorus in mud in which the phosphorus is extracted with benzene or isooctane. Gas chromatographic separation is achieved on a 2mx3mm column packed with 3% OV-1 or SE-30 on Chromosorb W maintained at 100 or 120°C respectively. The carrier gas was helium (80ml m 1). A flame photometric detector with a 526nm filter at 200°C was employed. Down to lpg of phosphorus could be determined. 

The high water-solubility of surfactants and their, often more polar, metabolites prevents direct application of gas chromatographic separation (GC) with appropriate detection. The necessary volatilisation without thermal decomposition can be achieved by derivatisation of the analytes, but these manipulations are time- and manpower-consuming and can be susceptible to discrimination. Additionally, each derivatisation step in environmental analysis is normally target-directed to produce volatile derivatives of the compounds to be determined. Unknown surfactants that are simultaneously present, but differ in structure and therefore cannot react with the derivatisation reagent, are discriminated under these conditions. 

There are, in fact, three theories that have gained virtually wide recognition and acceptance in describing a gas chromatographic separation, namely ... 

Another difficulty in the gas chromatographic separation of amino acids is the choice of detector and it may be necessary to split the gas stream and use two different detectors. The flame ionization detector, which is commonly used, is non-specific and will detect any non-amino acid components of the sample unless purification has been performed prior to derivatization. In addition the relative molar response of the flame ionization detector varies for each amino acid, necessitating the production of separate standard curves. As a consequence, although gas chromatography offers theoretical advantages, its practical application is mainly reserved for special circumstances when a nitrogen detector may be useful to increase the specificity. 

The new polysiloxanes are excellently suited as stationary phases for the gas chromatographic separation of the optical antipodes of different compounds classes over a temperature range from 70° to 240° C. 

Al-Thamir, W. K., Laub, R. J. and Purnell, J. H. J. Chromatog. 142 (1977) 3. Gas chromatographic separation of ail C1-C4 hydrocarbons by multi-substrate gas-sohd-hquid chromatography. 

Gas chromatographic separation may be facilitated, and important structural information may be obtained upon the formation of ... 

Investigations on the stereochemistry of chiral semiochemicals may be carried out by (gas) chromatographic separation of stereoisomers using chiral stationary phases, e.g. modified cyclodextrins [32]. Alter natively, formation of diastereomers (e.g. Mosher s ester or derivatives involving lactic acid etc.) may be followed by separation on conventional achiral stationary phases. Assignment of the absolute configuration of the natural product will again need comparison with an authentic (synthetic) reference sample. 

Note In FI-MS, the ionization efficiency is very low, because of the low probability for a neutral effusing from any inlet system towards the field emitter to come close enough to the whiskers. Consequently, FI-MS produces very low ion currents. The application of FI-MS is therefore restricted to samples that are too volatile for FD-MS or require gas chromatographic separation before. 

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