Subcritical fluids

Figure 7.4 The Subcritical Fluid Cliromatography range. This occupies the volume in the phase diagram below the locus of critical temperatures, above and below the locus of critical pressures, and is composed mostly of the more volatile mobile-phase component. Reproduced by peimission of the American Chemical Society.

C. Wolf and W. FI. Prrkle, Enantioseparations by subcritical fluid cliromatography at cryogenic temperatures , 7. Chromatogr. 785 173-178 (1997). 

Achiral-chiral chromatography has also been accomplished using subcritical fluid chromatography (Phinney et al., 1998). In this work, the structurally related [3-blockers, 1,4-benzodiazepines, and two cold medicines were separated using methanol or ethanol modified carbon dioxide mobile phases. The (3-blockers were separated using cyanopropyl and Chiracel OD columns connected in series. Likewise, an amino bonded phase and Chiracel OD column were used for the separation of the 1,4-benzodiazepines. Guaifenesin and phenylpropanolamine from cough syrup were separated on cyanopropyl and Chiralpak AD columns in series. 

Sandra, P, Kot, A., David, F. (1994). Subcritical fluid chromatography of coupled CSP columns for the separation of drug enantiomers. Chim. Oggi. 12, 33-36. 

Subcritical fluid 3545 Soil Semivolatile, nonvolatile Laboratory... 

Shaking or vortexing (can also be used for volatiles) Soxhlet Sonication Supercritical fluid Subcritical fluid... 

A screening approach was described in subcritical fluid chromatography for basic compounds by Stringham [52]. The analyzing conditions of the screening step are the following a flowrate of 2 mL/min, 180 bars of backpressure, and room temperature. The column for screening was Chiralpak AD-H, i.e. 5-p.m material was used. The mobile phase contained CO2, 20% of ethanol, and 0.1 % ethanesulfonic acid (ESA)... 

Stringham, R.W Chiral separation of amines in subcritical fluid chromatography using polysaccharide stationary phases and acidic additives. J. Chromatogr. A 2005, 1070, 163-170. 

Pirkle-type CSPs do not involve ionic interactions and therefore are almost exclusively operated in the normal-phase mode. The use of subcritical carbon dioxide based mobile phase, i.e., subcritical fluid... 

Extraction of stevia sweeteners from dried leaves can be accomplished with acetonitrile in the presence of calcium carbonate solution (116) or with boiling water adjusted to pH 9.0 (107). Ahmed and Dobberstein (117) extracted stevioside and rebaudioside A and C from dried leaves of S. rebaudiana in a micro-Soxhlet apparatus. They observed that chloroform/methanol provided the best results, compared to chloroform or to chloroform/methanol/water. Extraction of stevioside, rebaudioside A and C, and dulcoside A can also be performed by subcritical fluid extraction using C02 and methanol as a modifier. Such an extraction technique has been gaining popularity as an analytical tool because it is rapid, simple, and less expensive in terms of solvent cost (110). Beverages, tabletop sweeteners, beverages containing pulp, and candies are prepared as indicated in Sec. I.C (110,115,118). 

Supercritical fluid extraction [153,154], accelerated solvent extraction [68] and subcritical fluid extraction [107,155] have been studied. To reduce the equipment cost and the analysis time in the extraction process and sample preconcentration, a solid-phase microextraction method was proposed by Pawliszyn and coworkers [156-158]. 

Peytavin et al. [17] have reported on the chiral resolution of mefloquine, halofantrine, enpiroline, quinine, quinidine, chloroquine, and primaquine by subcritical fluid chromatography on a (S) naphthylurea column (250 X 4.6 mm ID). The mobile phase consisted of carbon dioxide, methanol, and triethylamine at a 3-ml/min flow rate. Except for primaquine and... 

Edder, R, Staub, C., Veuthey, J.L., Pierroz, I., Haerdi, W., Subcritical fluid extraction of opiates in hair of drug addicts, J. Chromatogr. B., 658, 75-86, 1994. 

A relatively new technique utilizing subcritical fluid extraction (SFE) was developed for the analysis of opioids in hair by Edder et al. Hair samples were washed. 

W. H. Pirkle and J. A. Burke, Enantioseparations by subcritical fluid chromatography at cryogenic temperatures J. Chromatogr. 5S1 (1991), 173-185. 

T. Loughlin, R. Thompson, G. Bicker, R Tway, and N. Grinberg, Use of subcritical fluid chromatography for the separation of enantiomers using packed column cellulose based stationary phase. Chirality 8 (1996), 157. 

Subcritical fluid chromatography using a carbon dioxide/methanol mobile phase has been performed on diastereo-meric mixtures of isoxazolines 28-30. 

Normal phases composed of hexane modified with 2-propanol have been successfully used with the 3,5-dimethylphenyl carbamate and para-toluoyl ester forms of the CD CSP. The P-CD CSP has been used in subcritical fluid chromatography with a mobile phase composed of carbon dioxide modified with methanol, ethanol, or 2-propanol (69). Under these conditions, racemic amides and phosphine oxides were enantiomerically resolved. 

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