Micellar enhanced fluorimetric determination of carbendazim in natural waters

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

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 degrees C was increased in the presence of C6S, alphaCD and hydroxypropyl-beta-CD (HPCD). The association constants determined by fluorescence enhancement showed weak interactions (K(A) approximately 10(1) to 10(2) M(-1)) between the fungicide with both CDs, whereas they were stronger with C6S (K(A) approximately 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 (phi(P:H)/phi(P)) were 2.00+/-0.05, 1.40+/-0.03 and 2.8+/-0.4 for C6S, alphaCD 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. (< or = 2%) by triplicate analysis. The method is rapid, direct and simple and needs no previous degradation or derivatization reaction.

Partial least-squares with residual bilinearization for the spectrofluorimetric determination of pesticides. A solution of the problems of inner-filter effects and matrix interferents

This paper demonstrates for the first time the power of a chemometric second-order algorithm for predicting, in a simple way and using spectrofluorimetric data, the concentration of analytes in the presence of both the inner-filter effect and unsuspected species. The simultaneous determination of the systemic fungicides carbendazim and thiabendazole was achieved and employed for the discussion of the scopes of the applied second-order chemometric tools: parallel factor analysis (PARAFAC) and partial least-squares with residual bilinearization (PLS/RBL). The chemometric study was performed using fluorescence excitation-emission matrices obtained after the extraction of the analytes over a C18-membrane surface. The ability of PLS/RBL to recognize and overcome the significant changes produced by thiabendazole in both the excitation and emission spectra of carbendazim is demonstrated. The high performance of the selected PLS/RBL method was established with the determination of both pesticides in artificial and real samples.

Fluorescence enhancement of Carbendazim in the presence of cyclodextrins and micellar media: a reappraisal

This study focuses on the spectrofluorimetric behavior of the pesticide carbendazim in the presence of selected organized assemblies and also on their potential analytical applications. The relatively weak fluorescence emission band of carbendazim is significantly enhanced by micellar media formed by sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, and decyltrimethylammonium bromide. The influence of the surfactant structures, concentrations, and working experimental conditions on the fluorescence spectra of carbendazim was thoroughly evaluated and discussed. Although the interaction of carbendazim with different cyclodextrins is rather weak, it was corroborated that the fluorescence intensity of this compound in the presence of (2-hydroxy)propyl beta-cyclodextrin is increased by a factor of two. Among the studied organized media, the cationic surfactant hexadecyltrimethylammonium bromide produced the largest signals for the compound of interest. Consequently, the optimal working conditions for the spectrofluorimetric determination of carbendazim in the presence of the latter detergent were analyzed, concluding that previous literature reports should be reconsidered.