Supercritical chromatography

For the validation of chromatographic methods a good starting point can be found in the EURACHEM/ WELAC document on Accreditation of Chemical Laboratories [30]. ASTM Committee E19 on Chromatography covers all forms of chromatography including gas, liquid, ion and supercritical chromatography. 

IUPAC defines supercritical chromatography as a separation technique in which the mobile phase is kept above (or relatively close to) its critical temperature and pressure. 

Todd, J., Mylchreest, I., Berry, T. and Games, D. Supercritical chromatography mass spectrometry with an ion-trap detector. Finnigan MAT IDT 46. 

Retention in supercritical chromatography is affected by the nature of both the mobile and the stationary phase. A variety of stationary phases, including high boiling liquids, polymer films, solid supports and chemically bonded monolayers, has been used. 

Adsorption equilibria and adsorption dynamics in supercritical fluids have been reported recently and it will be possible to apply the supercritical fluid to some new adsorptive separation processes. Fundamental informations on adsorption under supercritical conditions are necessary to design such processes. Supercritical chromatography has been used for study on the adsorption equilibria and adsorption dynamics. Adsorption of organics, i.e., benzene, toluene and m xylene, respectively, on MSC under supercritical conditions has already been reported in reference (Chihara, 1995). In the previous study, chromatographic measurements were made for the adsorption of benzene, toluene and m-xylene on MSC in supercritical CO2 mixed with benzene, toluene and m-xylene respectively. Moment analysis of the chromatogram was carried out. In the study, the organics used in the form of pulse were the same as organics mixed with supercritical CO2. The dependencies of adsorption equilibrium and micropore difliisivities on the amount adsorbed were obtained. 

A number of other substances have served as mobile phases in supercritical chromatography, including ethane, pentane, dichlorodifluoromethane, diethyl ether, and tetrahydrofuran. 

Accurate pressure- and ternperatiire-control facilities are required for supercritical chromatography. The mobile phase must be heated to the correct temperature in a spiral before the injection valve. The spiral, valve, column and detector should all be placed in an oven. A restrictor must be placed behind the detector so that the whole system can be maintained at a sufficiently high pressure. As columns it is possible to use either open capillaries, which allows us to obtain very high plate numbers, as well... 

The application of supercritical fluids, for example SCCO2, as an environmentally acceptable replacement for conventional solvents, is well documented in the industry. Based on the work of Zosel, the decaffeination of coffee and tea using SCCO2 was the first industrial use of this technology [1]. The advantages of supercritical fluids are not only useful in separation techniques, for example supercritical fluid extraction (SFE) or supercritical chromatography (SFC), their application as process solvents is well recognized [2, 3]. 

The sorption applications include regeneration of porous beds, preparative scale supercritical chromatography, simulated moving beds, thermal swing schemes, and adsorp-tion/desorptions cycles. Although initial applications of supercritical fluids in this domain were on regeneration of porous beds, more recent emphasis on fractionation best reflects... 

About 60,000 hquid crystals are known, and over 250 have been investigated as stationary phases in gas chromatography, high-pressure hquid chromatography, and supercritical chromatography. 

Supercritical chromatography is covered by Schneider in these proceedings. 

J. Todd, C. Mylchreest, T. Berry and D. Graves, Supercritical Chromatography Mass Spectroscopy with an Ion-Trap Detector, Finnegan MAT IDT Publication 46. 

Liquid ammonia and liquid sulphur dioxide appear to offer attractive possibilities for chromatographic purposes as both these substances, particular liquid sulphur dioxide, are very good solvents for organic substances. Such liquids would also lead to a unique form of supercritical chromatography (7). Furthermore, they are likely to ionize specific organic materials that otherwise do not normally ionize in water or are insoluble in... 

---