Determination of methomyl in grain using deep eutectic solvent-based extraction combined with fluorescence-based enzyme inhibition assays

A deep eutectic solvent (DES)-based extraction method is established to facilitate the determination of methomyl in grain via enzyme inhibition fluorescence. The environmentally-friendly DES was synthesized from proline and ethylene glycol and used as a green replacement for traditional extraction solvents that are generally toxic. The DES was added to grain samples and vortex extraction of methomyl, the supernatant was then collected for fluorescence detection. Biomass carbon quantum dots (CQDs) synthesized from millet were used as fluorescent probes. Acetylcholinesterase catalyzes the hydrolysis of acetylthiocholine iodide to thiocholine. The positively-charged thiocholine interacts electrostatically with the negatively-charged quantum dots resulting in the quenching of their fluorescent emission. The pesticide extract solution blocks the enzyme activity and thus recovers the fluorescent from the quantum dots. The fluorescence response was correlated with the amount of methomyl residue in the grain over the range 0.01 to 5 mg kg^-1. The limit of detection was found to be 0.003 mg kg^-1, and the limit of quantification 0.01 mg kg^-1. Recoveries of 86.5% to 107.8% were obtained using real samples, including millet, rice, wheat, and barley, with a relative standard deviation of less than 3.8%. The method is efficient and convenient and has good application prospects for extracting and detecting pesticides in grain samples.

A novel luminescent terbium-3-carboxycoumarin probe for time-resolved fluorescence sensing of pesticides methomyl, aldicarb and prometryne

The luminescence arising from lanthanide cations offers several advantages over organic fluorescent molecules: sharp, distinctive emission bands allow for easy resolution between multiple lanthanide signals; long emission lifetimes (μs-ms) make them excellent candidates for time-resolved measurements; and high resistance to photo bleaching allow for long or repeated experiments. A time-resolved (gated) luminescence-based method for determination of pesticides methomyl, aldicarb and prometryne in microtiterplate format using the long-lived terbium-3-carboxycoumarin in 1:3 metal:ligand ratio has been developed. The limit of detection is 1.20×10(6), 5.19×10(5) and 2.74×10(6)ng L(-1) for methomyl, prometryne and aldicarb, respectively. The quantum yield (QY=0.08) of Tb(III)-3-carboxycoumarin was determined using 3-(2-benzothiazolyl)-7-diethylamino-coumarin (coumarin 6). Stern-volmer studies at different temperatures indicate that collisional quenching dominates for methomyl, aldicarb and prometryne. Binding constants were determined at 303, 308 and 313 K by using Lineweaver-Burk equation. A thermodynamic analysis showed that the reaction is spontaneous with negative ΔG. Effect of some relevant interferents on the detection of pesticides has been investigated.

A kinetic spectrophotometric method for simultaneous determination of phenol and its three derivatives with the aid of artificial neural network

A novel kinetic spectrophotometric method was developed for determination of pyrocatechol, resorcin, hydroquinone and phenol based on their inhibitory effect on the oxidation of Rhodamine B (RhB) in acid medium at pH=3.0. A linear relationship was observed between the inhibitory effect and the concentrations of the compounds. The absorbance associated with the kinetic reactions was monitored at the maximum wavelength of 557nm. The effects of different parameters such as pH, concentration of RhB and KBrO(3), and temperature of the reaction were investigated and optimum conditions were established. The linear ranges were 0.22-3.30, 0.108-0.828, 0.36-3.96 and 1.52-19.76μg mL(-1) for pyrocatechol, resorcin, hydroquinone and phenol, respectively, and their corresponding detection limits were 0.15, 0.044, 0.16 and 0.60μg mL(-1). The measured data were processed by several chemometrics methods, such as principal component regression (PCR), partial least squares (PLS) and artificial neural network (ANN), and a set of synthetic mixtures of these compounds was used to verify the established models. It was found that the prediction ability of PLS, PCR and RBF-ANN was similar, however, the RBF-ANN model did perform somewhat better than the other methods. The proposed method was also applied satisfactorily for the simultaneous determination of pyrocatechol, resorcin, hydroquinone and phenol in real water samples.