Improved competitive indicator methods for the study of alpha-cyclodextrin complexes.

The competitive indicator method for studying molecular complexes is extended to systems forming 1:1 (SL) and 1:2 (SL2) complexes of substrate (S) and ligand (L). A modification is described for slightly soluble substrates, in which the presence of solid substrate establishes a constant concentration of uncomplexed substrate. These methods are applied to complexes of alpha-cyclodextrin with some aromatic substrates, with methyl orange as the indicator in acid solution; nitrazine yellow is introduced as an indicator for these studies in basic solution.