Determination of apparent association constants of steroid–cyclodextrin inclusion complexes using a modification of the Hummel–Dreyer method

A modified Hummel–Dreyer method was used to calculate the apparent association constants of steroid–cyclodextrin inclusion complexes. An external calibration technique was employed, using the y-intercept from a plot of peak area versus concentration to correct for sample solvent effects. Mobile phase temperature and sample diluent organic content were found to be critical factors affecting the accuracy and reproducibility of the results. For four of six sets of data, the modified Hummel–Dreyer method yielded statistically equivalent results to another HPLC method for determining apparent association constants. Limitations of the modified Hummel–Dreyer method are discussed. In particular, the accuracy of the method is poor when measuring small apparent association constants.