Development of a single fluorescence-based optosensor for rapid simultaneous determination of fungicides benomyl and thiabendazole in waters and commercial formulations

Review of Characteristics and Analytical Methods for Determination of Thiabendazole

Thiabendazole (TBZ) is a fungicide and anthelmintic drug commonly found in food products. Due to its toxicity and potential carcinogenicity, its determination in various samples is important for public health. Different analytical methods can be used to determine the presence and concentration of TBZ in samples. Liquid chromatography (LC) and its subtypes, high-performance liquid chromatography (HPLC) and ultra-high-performance liquid chromatography (UHPLC), are the most commonly used methods for TBZ determination representing 19%, 18%, and 18% of the described methods, respectively. Surface-enhanced Raman spectroscopy (SERS) and fluorimetry are two more methods widely used for TBZ determination, representing 13% and 12% of the described methods, respectively. In this review, a number of methods for TBZ determination are described, but due to their limitations, there is a high potential for the further improvement and development of each method in order to obtain a simple, precise, and accurate method that can be used for routine analysis.

Simultaneous Electrochemical Detection of Benzimidazole Fungicides Carbendazim and Thiabendazole Using a Novel Nanohybrid Material-Modified Electrode

In this work, a novel ZnFe₂O₄/SWCNTs nanohybrid was successfully synthesized as electrode material and applied to the simultaneous quantitative determination of carbendazim (CBZ) and thiabendazole (TBZ). The electrochemical behaviors of CBZ and TBZ on the ZnFe₂O₄/SWCNTs/GCE were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The electrochemical active area of modified electrode was calculated, which is nearly 5.5 times that of the bare electrode. The influence of various factors such as accumulation time, pH and scan rates, type of surfactant, and the electrochemical reaction mechanism was studied. The results showed that the reaction of CBZ/TBZ was controlled by adsorption/diffusion and was a quasi-reversible/an irreversible process at the ZnFe₂O₄/SWCNTs/GCE. In the pH 7.0 phosphate-buffered saline (PBS) containing 10.0 μg/mL CTAB, the electrochemical responses of CBZ and TBZ were separately investigated and were linearly dependent on their concentrations ranging from 0.5 to 100.0 μM, with relatively low detection limits of 0.09 and 0.05 μM, respectively. The concentration range for the simultaneous determination of CBZ and TBZ was 1.0-100.0 μM. Furthermore, with satisfactory results, the proposed electrochemical sensor was successfully applied to the determination of CBZ and TBZ in the real samples.

Dispersive liquid-liquid microextraction combined with non-aqueous capillary electrophoresis for the determination of imazalil, prochloraz and thiabendazole in apples, cherry tomatoes and grape juice

BACKGROUND

Fruit and vegetables are frequently treated with fungicides to reduce possible spoilage. As a result, fungicide residues may be accumulated in derived products. This important group of chemical compounds has been heavily regulated because of their potential toxicity. Therefore, a simple and rapid method to determine fungicides is desired.

RESULTS

A simple non-aqueous capillary electrophoresis (NACE) method based on dispersive liquid-liquid microextraction (DLLME) has been proposed for the determination of imazalil, prochloraz and thiabendazole fungicides in fruits and juice samples. Separation buffer consisted of a methanol-acetonitrile mixture (35:65, v/v) containing 30 mmol L⁻¹ ammonium chloride and 0.5% phosphoric acid. The optimum DLLME conditions were 80 µL trichloromethane as extraction solvent, 0.5 mL tetrahydrofuran as disperser solvent, sample solution pH at 6.0, 5% (w/v) NaCl and 10 s extraction time. Recoveries obtained for various samples ranged from 72% to 102%, with relative standard deviation lower than 6.4%. The limits of detection ranged from 0.47 to 0.72 µg kg⁻¹.

CONCLUSION

The proposed method takes the advantages of DLLME and NACE. It is rapid, accurate, sensitive and reproducible for the determination of imazalil, prochloraz and thiabendazole in fruit samples.

Flow injection analysis with on-line nylon powder extraction for room-temperature phosphorescence determination of thiabendazole

A fast and very selective flow-through phosphorescence optosensor was designed and characterized for the determination of the fungicide thiabendazole in water samples. For the first time, thiabendazole was determined using a flow-through optosensor based on the phosphorescence signals obtained when it is retained in a solid support. While thiabendazole does not phosphoresce in packing materials commonly used to fill the flow-cell, significant emission signals are observed when it is retained on nylon powder in the presence of iodide and sulfite. The experimental set-up was based on a flow-injection manifold coupled to an on-line phosphorescence detector containing nylon powder packed in a conventional flow-cell. Potassium iodide and sodium sulfite were added to sample aliquots to improve the thiabendazole phosphorescence and injected in the flow manifold using water as carrier. After the phosphorescence emission was registered, the analyte was eluted from the packed nylon with a 65% (v/v) methanol-water mixture. Optimal instrumentation, experimental and flow conditions were evaluated. Using a sample volume of 2000 microL, the analytical signal showed a very good linearity in the range 12.9-110 ng mL(-1), with a detection limit of 4.5 ng mL(-1), and a sample throughput of about 14 samples per hour. The effects of the presence of concomitant species in the thiabendazole phosphorescence signal were studied, and a comparison with the fluorescence nylon-powder optosensor was carried out and discussed. Finally, the applicability of the proposed optosensor was tested in water samples, and satisfactory recoveries ranging between 97% and 105% were obtained.

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.

Determination of poorly fluorescent carbamate pesticides in water, bendiocarb and promecarb, using cyclodextrin nanocavities and related media

The effect of native cyclodextrins (alpha, beta, or gammaCD with six, seven and eight glucose units, respectively), hydroxypropyl-beta-cyclodextrin (HPCD), chitosan (CHT) and glucose in water solution or water with n-propylamine (PA) as co-solvent upon the UV-vis and fluorescence properties of poorly fluorescent N-methyl carbamates pesticides (C) as bendiocarb (2,2-dimethyl-1,3-benzodioxol-4-ol methylcarbamate, BC) and promecarb (3-methyl-5-(1-methylethyl)phenol methylcarbame, PC) was examined. Fluorescent enhancement was found for both substrates with all CDs in water or PA-water except from PC with alphaCD. The addition of CHT increases the fluorescence of BC but decreases the fluorescence of PC, and glucose addition gives in both cases no spectral changes. Host-guest interaction was clearly determined by fluorescence enhancement with betaCD and HPCD with a 1:1 stoichiometry for the complexes (C:CD). The values obtained for the association constants (K(A), M(-1)) were (6+/-2)x10(2) and (2.3+/-0.3)x10(2) for BC:betaCD and BC:HPCD complexes, respectively. For PC:betaCD and PC:HPCD the values of K(A) were (19+/-2)x10(2) and (21+/-2)x10(2), respectively. The ratio of the fluorescence quantum yields for the bound and free substrates (phi(CCD)/phi(C)) was in the range 1.74-3.8. The limits of detection (L(D), microg mL(-1)) for the best conditions were (0.57+/-0.02) for BC with HPCD and (0.091+/-0.002) for PC with betaCD in water. Application to the analysis in pesticide spiked samples of tap water and fruit yields satisfactory apparent recoveries (84-114%), and for the extraction procedure in fruits and a commercial formulation, recoveries were of 81-98% and 104%, respectively. The method is rapid, simple, direct, sensitive and useful for pesticide analysis.

A new analytical application of nylon-induced room-temperature phosphorescence: Determination of thiabendazole in water samples

This paper discusses the first analytical determination of the widely used fungicide thiabendazole by nylon-induced phosphorimetry. Nylon was investigated as a novel solid-matrix for inducing room-temperature phosphorescence of thiabendazole, which was enhanced under the effect of external heavy-atom salts. Among the investigated salts, lead(II) acetate was the most effective in yielding a high phosphorescence signal. An additional enhancement of the phosphorescence emission was attained when the measurements were carried out under a nitrogen atmosphere. There was only a moderate increase in the presence of cyclodextrins. The room-temperature phosphorescence lifetimes of the adsorbed thiabendazole were measured under different working conditions and, in all cases, two decaying components were detected. On the basis of the obtained results, a very simple and sensitive phosphorimetric method for the determination of thiabendazole was established. The analytical figures of merit obtained under the best experimental conditions were: linear calibration range from 0.031 to 0.26 microg ml(-1) (the lowest value corresponds to the quantitation limit), relative standard deviation, 2.4% (n=5) at a level of 0.096 microg ml(-1), and limit of detection calculated according to 1995 IUPAC Recommendations equal to 0.010 microg ml(-1) (0.03 ng/spot). The potential interference from common agrochemicals was also studied. The feasibility of determining thiabendazole in real samples was successfully evaluated through the analysis of spiked river, tap and mineral water samples.