A

Silica

Figure 6 Optimized association between the optimized structures of (R)-propranolol (without carbon dioxide) and ChyRoSine-A CSP. (Reproduced with permission from Bargmann-Leyder N, Sella C, Bauer D, Tambute, A and Caude M (1995) Separation of ^-blockers using supercritical fluid chromatography: investigation of the chiral recognition mechanism using molecular modelling. AnalyticalChemistry 67: 952-958.)

2-propanol) are almost equivalent. Water should not be used since it decreases selectivity significantly.

As reported by Macaudiere and co-workers, the use of cyclodextrin CSPs in SFC allows particular selectivities to be obtained. A comparison between solute behaviour in reversed-phase and in normalphase liquid chromatography clearly demonstrated that SFC and reversed-phase liquid chromatography are two complementary techniques; this result has widened the range of cyclodextrin phase applications. Figure 9 shows the comparison of the separation of the 2-naphthyl and o-anisyl phosphine oxides on Cyclobond I in normal-phase LC and SFC. No or very weak enantiomeric resolution is achieved using normal-phase LC.

Enantiomeric separation of a variety of drugs and related compounds (ancymidol, coumachlor, ibuprofen, mephenytoin, tropicamide, verapamil, etc.) on an (S)-naphthylethylcarbamoylated-^-cyclo-dextrin phase using sub- and supercritical fluid chromatography has been accomplished by Williams and co-workers. Compounds previously resolved on native or derivatized cyclodextrin CSPs in LC using reversed-phase or polar organic mobile phases could be resolved in SFC using a simple carbon dioxide/methanol eluent. Resolution of cromakalim was

Figure 7 Optimized associations between the optimized structures of (R)- and (S)-propranolol (with carbon dioxide) and ChyRoSine-A CSP. (Reproduced with permission from Bargmann-Leyder N, Sella C, Bauer D, Tambute A and Caude M (1995) Separation of p-blockers using supercritical fluid chromatography: investigation of the chiral recognition mechanism using molecular modelling. AnalyticalChemistry 67: 952-958.)

Figure 7 Optimized associations between the optimized structures of (R)- and (S)-propranolol (with carbon dioxide) and ChyRoSine-A CSP. (Reproduced with permission from Bargmann-Leyder N, Sella C, Bauer D, Tambute A and Caude M (1995) Separation of p-blockers using supercritical fluid chromatography: investigation of the chiral recognition mechanism using molecular modelling. AnalyticalChemistry 67: 952-958.)

Figure 8 High-speed enantiomeric separation of (A) propranolol and (B) pindolol on ChyRoSine-A CSP. Operating conditions: column, 50 x 3.2 mm i.d.; mobile phase, carbon diox-ide/(ethanol containing 1 % (v/v) of n-propylamine) (80: 20, (v/v); flow rate 7.5 mL min-1 at 0°C; temperature, 27°C; pressure, 220 bar; UV detection at 224 nm. (Reproduced with permission from Bargmann-Leyder N, Thiebaut D and Vergne F etal. (1995) High speed chiral separation of ^-blockers by supercritical fluid chromatography on ChyRoSine-A. Chromatographia 39: 673-681.)

Figure 8 High-speed enantiomeric separation of (A) propranolol and (B) pindolol on ChyRoSine-A CSP. Operating conditions: column, 50 x 3.2 mm i.d.; mobile phase, carbon diox-ide/(ethanol containing 1 % (v/v) of n-propylamine) (80: 20, (v/v); flow rate 7.5 mL min-1 at 0°C; temperature, 27°C; pressure, 220 bar; UV detection at 224 nm. (Reproduced with permission from Bargmann-Leyder N, Thiebaut D and Vergne F etal. (1995) High speed chiral separation of ^-blockers by supercritical fluid chromatography on ChyRoSine-A. Chromatographia 39: 673-681.)

not obtained on the (S)-naphthylethylcarbamoylated-ft-cyclodextrin CSP using LC, but was readily accomplished using SFC (Figure 10). The separation of the enantiomers of N-(3,5-dinitrobenzoyl)valine methyl ester, ancymidol and proglumide was also obtained in a single run using carbon dioxide/methanol eluent, whereas the same separations in LC required three different mobile phases.

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