Vapour phase chromatography

Gas chromatography vapour-phase therm products resulting ft radicals and niirogi... 

Kiran, E. and GillheWi, J.K., Pyrolysis-Molecular Weight-Chromatography-Vapour Phase Infra Red Spectrophotometry An On Line System for Analysis of Polymers. In Developments in Polymer Degradation 2j. Grassle, N. (Ed), Appl. Sci. Publ. London (1979). 

More information has appeared concerning the nature of the side reactions, such as acetoxylation, which occur when certain methylated aromatic hydrocarbons are treated with mixtures prepared from nitric acid and acetic anhydride. Blackstock, Fischer, Richards, Vaughan and Wright have provided excellent evidence in support of a suggested ( 5.3.5) addition-elimination route towards 3,4-dimethylphenyl acetate in the reaction of o-xylene. Two intermediates were isolated, both of which gave rise to 3,4-dimethylphenyl acetate in aqueous acidic media and when subjected to vapour phase chromatography. One was positively identified, by ultraviolet, infra-red, n.m.r., and mass spectrometric studies, as the compound (l). The other was less stable and less well identified, but could be (ll). 

The major chromatographic techniques can also be categorised according to tbe nature of the mobile phase used -vapour phase chromatography for when a gas is the mobile phase and liquid chromatography for when a liquid is the mobile phase. 

In contrast to vapour phase chromatography, the mobile phase in liquid chromatography is a liquid. In general, there are four main types of liquid chromatography adsorption, partition, ion-chromatography, and gel filtration. 

Dried with Linde type 5A molecular sieves or Na2S04 and fractionally distd at reduced pressure. Alternatively, it was refluxed with, and distd from, BaO. Also purified by fractional crystn from the melt and distd from zinc dust. Converted to its phosphate (m 135°) or picrate (m 223°), which were purified by crystn and the free base recovered and distd. [Packer, Vaughn and Wong J Am Chem Soc 80 905 1958.] The procedure for purifying via the picrate comprises the addition of quinoline to picric acid dissolved in the minimum volume of 95% EtOH to yield yellow crystals which are washed with EtOH and air dried before recrystn from acetonitrile. The crystals are dissolved in dimethyl sulfoxide (previously dried over 4A molecular sieves) and passed through a basic alumina column, on which picric acid is adsorbed. The free base in the effluent is extracted with n-pentane and distd under vacuum. Traces of solvent are removed by vapour phase chromatography. [Mooman and Anton J Phys Chem 80 2243 1976.]... 

Small amounts of pyridine have been purified by vapour-phase chromatography, using a 180-cm column of polyethyleneglycol-4(X) (Shell 5%) on Embacel (May and Baker) at 100°, with argon as carrier gas. The Karl Fischer titration can be used for determining water content. A colour test for pyrrole as a contaminant is described by Biddiscombe et al. [J Ghent Soc 1957 1 954]. 

S. W. Green, The quantitative analysis of mixtures of chlorofluoromethanes in vapour phase cliromatography , in Vapour Phase Chromatography D. H. Desty (Ed.), Butterwoiths, London, pp. 388 (1957). 

In cases of quite volatile compounds, vapour-phase chromatography gives excellent specificity, although the usefulness of the method is limited because of the low vapour pressures and poor heat resistance of many organometallic compounds. 

Figure 7.10 Typical optical arrangements employed for detection of (a) vapour phase (b) liquid phase and (c) solid chromatographic phases. After White [167], Reprinted from R. White (ed.), Chromatography/Fourier Transform Infrared Spectroscopy and Its Applications Marcel Dekker Inc., New York, NY (1990), by courtesy of Marcel Dekker Inc.

Gas chromatography is a most favourable case for interfacing to a mass spectrometer, as the mobile phases commonly used do not generally influence the spectra observed, and the sample, being in the vapour phase, is compatible with the widest range of mass-spectral ionisation techniques. The primary incompatibility in the case of GC-MS is the difference in operating pressure for the two hyphenated instruments. The column outlet in GC is typically at atmospheric pressure, while source pressures in the mass spectrometer range from 2 to... 

TLC may be combined with column chromatography and vapour-phase chromatography as discussed here briefly ... 

Principle The underlying principle of head space gas chromatography is the analysis of the vapour phase in equilibrium with the solid or liquid phase. 

V2. Van Meter, J. C., Buckmaster, H. S., and Shelley, L. L., Concurrent assay of phenobarbital and diphenylhydantoin in plasma by vapour-phase chromatography. Clin. Chem. 16, 135-138 (1970). 

Chromatography is often used with advantage for the purification of small amounts of complex organic mixtures, either as liquid chromatography or as vapour phase (gas) chromatography. 

The mobile phase in vapour phase chromatography is a gas (e.g. hydrogen, helium, nitrogen or argon) and the stationary phase is a non-volatile liquid impregnated onto a porous material. The mixture to be purified is injected into a heated inlet whereby it is vaporised and taken into the column by the carrier gas. It is separated into its components by partition between the liquid on the porous support and the gas. For this reason vapour-phase chromatography is sometimes referred to as gas-liquid chromatography. 

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