Liquid Chromatography - Macrocyclic Glycopeptide Phases 4
This material can also be bonded to 5 mm silica gel particles by multiple covalent linkages. Teicoplanin contains 20 chiral centers surrounding four molecular 'pockets' or 'cavities'. Neighboring groups are strongly polar and aromatic rings provide ready polarizability. The proposed structure of Teicoplanin is shown in figure 51. This stationary phase is claimed to be complementary to the Vancomycin phase and can be used with the same types of mobile phase, one often providing chiral selectivity, when the other does not. Teicoplanin can be used in a reversed phase mode using strongly polar mixtures such as acetonitrile/aqueous buffer : 10/90 v/v, THF/aqueous buffer 10/90 : v/v, and ethanol/aqueous buffer : 20/80 v/v). It can also be used as a polar stationary phase using n-hexane/ethanol mixtures as the mobile phase. In some cases it is advisable to control the pH even when the solutes are not ionic, suitable buffers being ammonium nitrate and triethylamine acetate.
The separation of the Propranolol enantiomers on Teicoplanin is shown in figure 52.
Figure 52 The Separation of the Enantiomers of Propranolol Employing Different Acid/Base Ratios