Spectrofluorimetric determination of benzoimidazolic pesticides: Effect of p-sulfonatocalix[6]arene and cyclodextrins

Abstract

The effect of the addition of a macrocyclic host ( H) such as p-sulfonatocalix[6]arene ( C6S), native and modified cyclodextrins ( CDs), on the fluorescence of benzoimidazolic fungicides ( P), like Benomyl ( BY) and Carbendazim ( CZ), has been studied. The fluorescence of BY in water at pH 1.000 and 25.0 °C was increased in the presence of C6S, α CD and hydroxypropyl-β- CD ( HPCD). The association constants determined by fluorescence enhancement showed weak interactions ( K A ∼ 10 1 to 10 2 M −1) between the fungicide with both CDs, whereas they were stronger with C6S ( K A ∼ 10 5 M −1). Molecular recognition of BY for C6S was mainly attributed to electrostatic interactions, and for CDs to the hydrophobic effect and hydrogen bond formation. On the other hand, the fluorescent behaviour of CZ in the presence of C6S at pH 6.994 was interpreted as the formation of two complexes with 1:1 ( P:H) and 1:2 ( P:H 2 ) stoichiometry, the latter being less fluorescent than the free analyte. Relative fluorescence quantum yield ratios between the complexed and free BY ( ϕ P:H / ϕ P) were 2.00 ± 0.05, 1.40 ± 0.03 and 2.8 ± 0.4 for C6S, α CD and HPCD, respectively. The analytical parameters improved in the presence of C6S and CDs. The best limit of detection ( L D, ng mL −1) was 17.4 ± 0.8 with HPCD. The proposed method with C6S and HPCD was successfully applied to fortified samples of tap water and orange flesh extract with good recoveries (91–106%) and R.S.D. (≤2%) by triplicate analysis. The method is rapid, direct and simple and needs no previous degradation or derivatization reaction.