Supercritical fluid chromatography enantiomers separation

Beside the use of MIPs in conventional HPLC, Mi-polymers may also be established in supercritical fluid chromatography, which is characterized by faster equilibration times combined with the use of the environmental friendly C02 as mobile phase. Although preliminary results show relatively broad peaks, chiral separation could be performed based on polymers imprinted with an enantiomer. However, the long-term stability of the photochemically generated polymers seems to be a problem [89]. 

Figure 17. Enantiomer separation by supercritical fluid chromatography of 7-chloro-2,3.4,5-tetrahydro-l-methyl-5-phenyl-1,4-benzodiazepin-2(l//)-one (dihydrodiazepam) on a 2.5 m x0.05 mm (i.d.) fused silica capillary column, containing immobilized octamethylenc-Chirasil-Dex [carbon dioxide at 90CC. density programmed from 0.31 g/mL (130 atm) at 0.0029 g/mL min 1 after an initial 2.0-min period at 0.31 g/ mL]130.

The specific development of a batch process is illustrated in the following example, namely the separation of the enantiomers of racemic trans-stilbene oxide (TSO) [28], For this example, supercritical fluid chromatography was particularly appropriate for the resolution. 

Phinney KW, Sub- and supercritical fluid chromatography for enantiomer separations, in Chiral Separation Techniques A Practical Approach, (Suhramanian G, Ed.), p. 299, VCH Verlag, Weinheim, Germany (2001). 

The racemate of 1,3,2-benzodithiazole 1-oxide 42 was separated by supercritical fluid chromatography on the (A j )-Whelk-( )l column with supercritical carbon dioxide containing 20% methanol as a mobile phase. Peak areas of enantiomers prior to and after the separation, used for the calculation of the enantiomerization barrier, were detected by computer-assisted peak deconvolution of peak clusters registered on chromatograms using computer software <2002CH1334>. 

Steuer et al. demonstrated the use of supercritical fluid chromatography in the separation of enantiomers of 1,2 amino alcohols, namely pindolol, metoprolol, oxprenolol, propranolol, and DPT 201-106 using ionpairing modifiers [21]. The mobile phase consisted of carbon dioxide mixed with acetonitrile containing triethylamine as a counterion and /V-benzo-xycarbonylglycyl-L-proline as a chiral counterion. They found that the ca-... 

M. Jung and V. Schurig, Extending the scope of enantiomer separation by capillary supercritical fluid chromatography on immobilized polysiloxane anchored permethyl-B-cyclodextrin (Chirasil-Dex), J. High Resolut. Chromstogr., 76 215 (1993). 

Williams, K.L. and Sander, L.C. 1997. Enantiomer separations on chiral stationary phases in supercritical fluid chromatography. Journal of Chromatography A, 785 149-58. 

Chiral Stationary Phases for GC and HPLC. Enantiomerically pure NEA has been used to prepare a variety of chiral stationary phases for liquid, gas, and supercritical fluid chromatography. These stationary phases are used to separate enantiomers without derivatization of the substrate with a chiral agent. 

TLC has also been used for the separation of diastereomeric derivatives of enantiomers, but this form of chromatography has not attained widespread use in indirect resolutions. Other chromatographic techniques, for example, supercritical fluid chromatography, capillary electrophoresis, countercurrent chromatography, etc., have not received much attention in indirect enantioseparation. 

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