Interaction of β-cyclodextrin with cetyltrimethylammonium bromide in the presence of neutral red and its application to the spectrophotometric determination of β-cyclodextrin

The effects of addition of beta-cyclodextrin (beta-CD) to the neutral red-cetyltrimethylammonium bromide (CTAB) associates in pH 7 phosphate buffer solutions were investigated. Addition of beta-CD to neutral red-CTAB association causes decomposition of the associate by displacement of neutral red with beta-CD. The inclusion complex of CTAB with beta-CD is more stable than that with neutral red. The results indicate that formation of inclusion complex of CTAB with beta-CD prevents its association with neutral red, and inclusion complex formation of beta-CD and neutral red in the presence of CTAB takes place after total consumption of CTAB. The competition of beta-CD and neutral red on the interaction with CTAB can be used for the simple, rapid and sensitive spectrophotometric determination of beta-CD.