Page 314 - Chiral Separation Techniques

306 12 Sub- and Supercritical Fluid Chromatography for Enantiomer Separations

Fig. 12-3. Separation of ingredients of an expectorant syrup, on a Chiralpak AD CSP (a) and the
coupled cyano/Chiralpak AD CSP (b). Chromatographic conditions: 10 % methanol with 0.5 % iso-
–1
propylamine in carbon dioxide, 2.0 mL min , 15 MPa, 30 °C. Peaks are benzoic acid (BA), guaifenesin
(GF), and phenylpropanolamine (PPA).

12.3.4 Preparative Separations

Packed column SFC has also been applied to preparative-scale separations [42]. In
comparison to preparative LC, SFC offers reduced solvent consumption and easier
product recovery [43]. Whatley [44] described the preparative-scale resolution of
potassium channel blockers. Increased resolution in SFC improved peak symmetry
and allowed higher sample throughput when compared to LC. The enhanced resolu-
tion obtained in SFC also increases the enantiomeric purity of the fractions col-
lected. Currently, the major obstacle to widespread use of preparative SFC has been
the cost and complexity of the instrumentation.