Cyclodextrin-Enhanced Photo-Induced Fluorescence of Tau-Fluvalinate, Molecular Modelling of Inclusion Complexes and Determination in Natural Waters

The effect of adding organized supramolecular systems such as -cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) upon the photochemically-induced fluorescence (PIF) spectral properties of tau-fluvalinate (TFV) in aqueous solutions were examined. The influence of pH, UV irradiation time and photoproduct stability on the cyclodextrin-enhanced photochemically-induced fluorescence intensity was also investigated. The spectral changes associated with the inclusion process yielded values for the formation constants of TFV inclusion complexes between 450 and 640 M-1, were calculated using the nonlinear iterative regression approach least squares. In addition, host-guest interaction was clearly determined by PIF enhancement and a 1:1 stoichiometry was found for the β-CD and HP-β-CD complexes formed with TFV. The negative free energy (∆G°) value indicated that, the reaction of TFV with cyclodextrins was thermodynamically favorable. Furthermore, the structures of inclusion complexes of TFV with cyclodextrins were elucidated by 3-21G ab-initio calculations. The limits of detection and quantification obtained ranged between 1.3 to 4.0 ng mL-1 and from 4.4 to 13.0 ng mL-1 in β-CD and HP-β-CD media, respectively. The analytical application on tap and river water samples yielded satisfactory mean recoveries going from about 98.12 to 102.97 %. Due to its sensitivity and ease of use, this method can be reliably applied to routine analysis.