Determination of the Association Constant of Alpha and Beta Cyclodextrins Using Methyl Orange

This work describes a method for determination of the association constants of cyclodextrins (CDs) using methyl orange (MO) dye and complexation theory. The best operational conditions were complexation between the dye and the CDs at pH 3.0, using disodium citrate-phosphate buffer, a detection wavelength of 500 nm, and a maximum dye concentration of 0.045 × 10 -3 mol/L. Under these conditions, the constants obtained were 2527/M for the complex formed between the α-CD and MO, and 952/M for the complex formed between the β-CD and MO. In both cases, the molar absorptivity of the complexes diminished by almost a third after complexation with the CDs. These values can be used with complexation theory to model the values of the constants for association between CDs and other substances.