Complexation study of diclofenac with β-cyclodextrin and spectrofluorimetric determination

Abstract

The inclusional complexation between the anti-inflammatory pharmaceutical diclofenac and β-cyclodextrin (β-CD) was studied by potentiometry, spectrophotometry and spectrofluorimetry, in both acid and neutral pH. Guest–host 1∶1 stoichiometries for the complexes in both media were determined, and their equilibrium constants were calculated. The values obtained from the different methods used are in very good agreement and are in the order of 10³. From the analysis of the pK_a value for diclofenac in both the absence and presence of β-CD (4.84 and 4.90 respectively), it was inferred that in the inclusion complex the carboxylic group is located outside the cavity. Further structural characterization of the inclusate was carried out by means of ¹H NMR spectra and AM1 semiempirical calculations. Based on the obtained results, a spectrofluorimetric method for the determination of diclofenac in the presence of β-CD was developed in the range of 0–5 µg ml^–1. Better limits of detection (0.03

µg ml^–1) and quantification (0.1 µg ml^–1) were obtained in this latter case with respect to those obtained in the absence of β-CD. The method was satisfactorily applied to the quantification of diclofenac in pharmaceutical preparations.