An improved synthesis of disulfides linked β-cyclodextrin dimer and its analytical application for dequalinium chloride determination by spectrofluorimetry

An improved synthesis of β-cyclodextrin (β-CD) dimer, containing two β-CD moieties that are linked through their sides by disulfides was presented. The dimer was characterized by means of IR, 1H NMR and elemental analysis. The inclusion complexation behavior of β-cyclodextrin dimer with dequalinium chloride (DQC) was studied in an aqueous NH4Ac-HAc buffer solution of pH 4.00 at room temperature by spectrofluorimetry. The apparent association constant of the complex was 1.67 × 104 l mol−1, which showed higher affinity than native β-CD (Ks = 4.99 × 102 l mol−1). Based on the significant enhancement of fluorescence intensity of DQC, a spectrofluorimetric method with high sensitivity and selectivity was developed for the determination of DQC in bulk aqueous solution in presence of β-CD dimer. The linear range was 6.38-1.60 × 103 ng ml−1with the detection limit 1.9 ng ml−1. There was no interference from the excipients normally used in tablets and serum constituents. The proposed method was successfully applied to the determination of DQC in tablets and serum.