Spectrofluorimetric study of the β-cyclodextrin–dapsone–linear alcohol supramolecular system and determination of dapsone Original Research Article

Dapsone (DDS) forms a 1:1 supramolecular complex with β-cyclodextrin (β-CD) both in the absence and presence of linear alcohols. The apparent association constants (Kapp) were measured using a steady-state fluorescence method. Kapp decreases linearly with an increasing number of carbon atoms in the chain of the alcohol. We attribute this to a competition between dapsone and linear alcohol for the β-CD hydrophobic cavity as detailed analysis of Kapp as a function of the concentration of alcohol suggests that the interactions in the β-CD–dapsone–linear alcohol system do not result in the formation of ternary supramolecular complex. Quenching the fluorescence of dapsone with NaI shows that the β-CD cavity acts as a shield against contact between dapsone and this aqueous phase quencher, while addition of alcohols inhibits this protective effect. This again suggests that alcohols occupy the space within the β-CD cavity with the result that dapsone molecules are forced to reside in the aqueous environment. Based on the significant enhancement of the fluorescence intensity of dapsone produced through complex formation, a spectrofluorimetric method for the determination of dapsone in bulk aqueous solution in the presence of β-CD is developed. The linear relationship between the fluorescence intensity and dapsone concentration was obtained in the range of 3.39 to 1.50×103 ng ml−1, with a correlation coefficient (r) of 0.9998. The detection limit was 1.02 ng ml−1. There was no interference from the excipients normally used in tablet formulations. The application of the present method to the determination of dapsone in tablets and human plasma gave satisfactory results and was compared with the pharmacopoeia method.