Determination of the binding constant of salbutamol to unmodified and ethylated cyclodextrins by affinity capillary electrophoresis

This paper describes a capillary electrophoretic method for the accurate determination of the binding constants (K) for inclusion complexes of beta-cyclodextrin (beta-CD) and ethylated beta-cyclodextrin (Et-beta-CD) with salbutamol. The model is designed to compensate for the change in viscosity caused by CD addition, which was shown to greatly affect the measurements, The influence of several operating parameters, e.g. temperature, pH of the running buffer and voltage, on the binding constants is discussed. The values for K obtained for beta-CD and Et-beta-CD are compared, and it is concluded that Et-beta-CD has a greater affinity for salbutamol than beta-CD. For the case of limited modified-CD solubility, a method is proposed to estimate the affinity of salbutamol for the CD. Finally, we demonstrate that the described method can efficiently predict the release-rate of a drug complexed with a given CD.