Spectrofluorimetric determination of diclofenac in the presence of α-cyclodextrin

This study focuses on the complex formed between α-cyclodextrin (CD) and the anti-inflammatory drug diclofenac in aqueous solution and also on its potential analytical applications. It was corroborated that the fluorescence emission band of diclofenac is significantly intensified in the presence of α-CD. From the changes in the fluorescence spectra, it was concluded that α-CD forms a 1:1 inclusional complex with diclofenac and its equilibrium constant was calculated to be 1.20(3)×103 M−1. With the purpose of characterizing the inclusion complex, the acid–base behaviour of diclofenac in both the presence and absence of α-CD was spectrophotometrically investigated. From the results obtained, it was inferred that both the carboxyl and the secondary amino groups of the guest molecule remain outside the cyclodextrin cavity. Further details on the complex structure was obtained by 1H NMR measurements and semiempirical calculations. In addition to the analysis of the α-CD–diclofenac interaction, a new approach for the quantification of diclofenac in the presence of α-CD is described in the range 0–5 μg ml−1. An application of the method to the determination of the studied drug in pharmaceutical preparations is shown.