Binding constant dependency of amphetamines with various commercial methylated beta-cyclodextrins

Cyclodextrins play an important role in enantioselective separations. They represent the major class of chiral selectors used by capillary electrophor esis. Unfortunately, the purity of commercial cyclodextrins is often not we ll characterized, and similar selectors sold by various suppliers may show totally different enantioselectivities. In this study, the composition of s everal commercial methylated-beta-cyclodextrins is evaluated by means of pr eviously developed analytical methods. Then, different calculation methodol ogies, such as graphical determinations, as well as nonlinear or linear reg ression approaches, are evaluated in order to calculate the binding constan ts of inclusion complexes formed by some amphetamine derivatives with methy lated-beta-cyclodextrins. The nonlinear curve-fitting methodology proves to be the most suitable for these determinations. Comparisons are made betwee n the different selectors and several hypotheses are proposed concerning th e formation of the inclusion complex. Finally, enantiomeric resolutions are evaluated for these selectors and conclusions drawn about the knowledge of selector composition.