Enantiomeric Separations of Terbutaline by CE with a Sulfated β-Cyclodextrin Chiral Selector:  A Quantitative Binding Study

Sulfated β-cyclodextrin, a negatively charged chiral selector, was used for the enantiomeric separation of racemic terbutaline by capillary electrophoresis. Chiral separation was found to increase with decreasing cyclodextrin concentration. Host−guest complex binding constants for this system were determined by UV difference spectroscopy (K av = 1490 M-1) and by CE under conditions of minimal EOF and reversed polarity (K 1 = 1730 M-1, K 2 = 1590 M-1, α = 1.09). The effect of organic modifiers, methanol, and acetonitrile was also studied over a wide range of modifier concentrations. Binding constants decreased while selectivity increased with increasing organic modifier concentration (10% MeOH: K 1 = 1590 M-1, K 2 = 1130 M-1, α = 1.41. 10% ACN: K 1 = 1320 M-1, K 2 = 870 M-1, α = 1.52). Experimental results are discussed in the context of existing separation models.