Indirect capillary electrophoresis with 8-anilino-1-naphthalenesulfonic acid as a fluorescence probe for determining the apparent stability constant of an inclusion complex formed between a cyclodextrin and a solute

An indirect capillary electrophoresis (CE) method was developed based on two competitive chemical equilibria for determining the stability constant of an inclusion complex formed between a cyclodextrin and a solute. 8-Anilino-1-naphthalenesulfonic acid was employed as a fluorescence probe. A linear relationship between mobility difference and concentration of uncomplexed ligand was theoretically established and experimentally verified. The principle of the method was explained using an example of determining stability constant of an inclusion complex formed between a ligand of hydroxypropyl-β-cyclodextrin and a solute of amantadine. The stability constant was determined to be ∼2·102 M−1. It was calculated without knowledge of the mobility of the complex measured at saturating ligand concentrations. This indirect method can be applied to solutes and ligands lacking signal response on the selected detector in the CE. In addition, the indirect method is valid for both charged and neutral solutes and ligands.