Vancomycin is a very stable chiral stationary phase, has a relatively high sample capacity, and when covalently bonded to the silica gel, has multiple linkages to the silica gel surface. It can either be used with mobile phases with a high water content, as a reversed phase, or with a high solvent content, as a largely polar stationary phase. For example, when used as a reversed phase the strongly polar THF–water mixtures would be very effective mobile phases. Conversely, when used as a polar stationary phase, n-hexane–ethanol mixtures would be more appropriate. Vancomycin has a number of ionizing groups and, thus, can be used over a range of different pH values (pH 4.0 to 7.0) and exhibit a wide range of retention characteristics and chiral selectivities.

Ammonium nitrate, triethylammonium acetate and sodium citrate buffers have all been used satisfactorily with this stationary phase. Other than controlling the pH, the effect of the chosen buffer has little or no effect on chiral selectivity. This is verified by the chromatograms shown in figure 53.

Figure 53 The Separations of the Isomers of Terbutaline Employing Different Buffer Solutions

It is seen that virtually the same selectivity is obtained from all three buffers irrespective of the actual chemical nature of the buffers themselves. However, although the difference is exceedingly small, the slightly greater separation ratio obtained from the buffer containing triethylamine might reflect the relatively strong dispersive character of the ethyl groups in the buffer molecule. The enthalpy contributions to retention can be strongly dispersive, and/or strongly polar, or result from induced dipole interactivity.