An alternative approach for carbaryl determination based on the change in the oscillation period of the Belousov-Zhabotinsky (BZ) reaction under the addition of carbaryl is demonstrated. The oscillations were observed by spectrophotometric measurement at 320 nm, corresponding to the maximum absorption wavelength of cerium(IV) catalyst. The oscillation periods increase with the carbaryl concentrations, which can be discussed based on the Field-Körös-Noyes (FKN) mechanism. The increase of oscillation periods is proportional to the concentration of carbaryl in the range of 0.1-200 mg L-1 with the regression coefficient of 0.9938. The limits of detection and quantification were 0.044 and 0.147 mg L-1, respectively. The precisions in terms of intra-day and inter-day measurements were efficient with relative standard deviation (RSD) lower than 2.1%. Accuracy of carbaryl in different water samples was obtained with high recoveries in the range of 94-106% and also comparable to the results of high performance liquid chromatography (HPLC) analysis. The proposed method is precise, cost-effective and can be alternatively employed for the screening and determination of carbaryl residues in water samples.

A method using micellar precipitation process using cationic surfactant cetyltrimethyl ammonium bromide at ambient temperature was investigated for simultaneous determination of benzimidazoles coupled with high-performance liquid chromatography (HPLC) analysis. The studied benzimidazoles was selected as model compounds including thiabendazole, albendazole, mebendazole, and fenbendazole. The experimental parameters affected the extraction efficiency, including the kind and concentration of salt, pH, concentration of CTAB, volume of 1-octanol, and the centrifugation extraction time, was optimized. The optimum extraction condition: 0.030 mol L-1 CTAB, 10% (m/v) NaCl, pH 4.0, 300 µL 1-octanol and centrifugation time 10 min. Under optimum conditions, enrichment factors of between 60 and 90 fold were obtained, leading to lower limit of detection in the range of 0.5-0.7 µg L-1, depending on the analytes. The calibration range of the method was linear over the wide range of 0.5-1000 µg L-1, with correlation coefficients more than 0.999. Finally, the proposed method was successfully applied in the analysis of benzimidazoles in milk samples.

Methyl salicylate based dispersive liquid-liquid microextraction method of benzimidazole fungicides (i.e., carbendazim, thiabendazole and fluberidazole) in water samples and analysis by high performance liquid chromatography has been firstly developed. The target fungicides in aqueous sample were extracted under the selected conditions of 250 µL of methyl salicylate without disperser solvent and 1.0% (m/v) sodium acetate without pH adjustment. The preconcentration factor and extraction recovery were obtained in the range of 24-38 and 54-85%, respectively. Limits of detection ranged from 0.03 to 0.05 µg L–1, while limits of quantification were in the range of 0.20-0.50 µg L–1. Recoveries at three spiked concentration levels of 5, 10, and 50 µg L–1 were obtained in the range of 74.1-118.4%, with the relative standard deviation (RSD) below 11%. The developed method was simple, rapid, low cost, and reliable for trace determination of the studied fungicides.