Simultaneous Determination of Eight Pesticide Residues in Cowpeas by GC-ECD

Monoclonal Antibody-Based Colorimetric Lateral Flow Immunoassay for the Detection of Pyridaben in the Environment

Pyridaben, a broad-spectrum pyridazinone acaricide that is widely used in agricultural production, can induce neurotoxicity and reproductive abnormalities, and is highly toxic to aquatic organisms. In this study, a pyridaben hapten was synthesized and used to prepare monoclonal antibodies (mAbs), among which 6E3G8D7 showed the highest sensitivity in indirect competitive enzyme-linked immunosorbent assay, with a 50% inhibitory concentration (IC₅₀) of 3.49 ng mL^-1. The mAb, 6E3G8D7, was further applied to a gold nanoparticle-based colorimetric lateral flow immunoassay (CLFIA) for pyridaben detection, according to the signal intensity ratio of the test line to the control line, which showed a visual limit of detection of 5 ng mL^-1. The CLFIA also showed high specificity and achieved excellent accuracy in different matrices. In addition, the amounts of pyridaben in blind samples detected by the CLFIA, were consistent with high-performance liquid chromatography. Therefore, the developed CLFIA is considered a promising, reliable, and portable method for pyridaben on-site detection in agro-products and environmental samples.

Research and Application of In Situ Sample-Processing Methods for Rapid Simultaneous Detection of Pyrethroid Pesticides in Vegetables

A novel rapid and cost-effective pre-processing method for the simultaneous determination of pyrethroid pesticides in vegetables has been developed and validated. The process of pesticide extraction was carried out by the QuEChERS (quick, easy, cheap, effective, rugged and safe) method combined with filtration by filter paper, and cleanup was carried out by the multi-plug-filtration-cleanup (m-PFC) method with no centrifuge program during the whole process. The pre-processing method is optimized for gas chromatography (GC). The process is convenient and time saving, requiring just a few seconds per sample. The recovery rate (70–120%), limit of detection (0.0001–0.007 mg/kg), precision (0.2–9.3%) and accuracy for each analyte were determined in 10 representative vegetables with good results. Finally, the feasibility of the developed method was further confirmed by the successful determination of pyrethroid-pesticide residues in pyrethroid-containing practical samples within the processing method coupled with thin-layer chromatography and a colloidal-gold test strip.

Determination, dissipation dynamics, terminal residues and dietary risk assessment of thiophanate-methyl and its metabolite carbendazim in cowpeas collected from different locations in China under field conditions

BACKGROUND

Thiophanate-methyl and its metabolite carbendazim are broad-spectrum fungicides used on many crops. The residues of these chemicals could result in potential environmental and human health problems. Therefore, investigations of the dissipation and residue behaviors of thiophanate-methyl and its metabolite carbendazim on cowpeas and associated dietary risk assessments are essential for the safety of agricultural products.

RESULTS

A simple analytical approach using liquid chromatography with tandem mass spectrometry was developed and validated for the determination of thiophanate-methyl and carbendazim concentrations in cowpeas. Good linearity (R²  > 0.998) was obtained, and the recoveries and relative standard deviations were 80.0-104.7% and 1.4-5.2%, respectively. The dissipation rates of thiophanate-methyl, carbendazim and total carbendazim were high (half-lives of 1.61-2.46 days) and varied in the field cowpea samples because of the different weather conditions and planting patterns. Based on the definition of thiophanate-methyl, the terminal residues of total carbendazim in cowpea samples were below the maximum residue limits set by Japan for other legumes. The acute and chronic risk quotients of three analytes were 0.0-27.6% in cowpea samples gathered from all terminal residue treatments, which were below 100%.

CONCLUSION

An optimized approach for detecting thiophanate-methyl and carbendazim in cowpeas was applied for the investigation of field-trial samples. The potential acute and chronic dietary risks of thiophanate-methyl, carbendazim and total carbendazim to the health of Chinese consumers were low. These results could guide the safe and proper use of thiophanate-methyl in cowpeas and offer data for the dietary risk assessment of thiophanate-methyl in cowpeas. © 2021 Society of Chemical Industry.

Headspace Solid-Phase Microextraction: Validation of the Method and Determination of Allyl Isothiocyanate Persistence in Cowpea Beans

Essential oils are widely recognized as an efficient and safe alternative for controlling pests in foods. However, a few studies have determined the persistence of these compounds in stored grains. The present study optimized and validated a fast and effective method for extraction and quantification of allyl isothiocyanate (AITC-the main component of mustard essential oil) residue in cowpea beans. It also investigated the persistence of this substance in the grains. The proposed method employs headspace solid-phase microextraction (HS-SPME) and gas chromatography with a flame ionization detector (GC/FID). For optimizing it, a central composite design (CCD) was used, where the best conditions for the extraction of the AITC were achieved using 15 min fiber exposure at 30 °C. The performance of the method was assessed by studying selectivity, linearity, limits of detection (LOD) and quantification (LOQ), precision, and accuracy. The LOD and LOQ for AITC were 0.11 and 0.33 μg kg^-1, respectively. The determination coefficient (R ²) was above 0.99. The relative recovery rate ranged from 108.2 to 114.8%, with an interday coefficient of variation below 9%. After 36 h, no residue was detected in the samples, demonstrating that the AITC has low persistence and can be safely used as a bioinsecticide for grains.

Method validation for bifenthrin emulsifiable concentrate and uncertainty calculation using gas chromatographic approach

Background

Bifenthrin is the third-generation synthetic pyrethroid insecticide having an effective control on the pest of cotton, vegetable, and fruits. This study is focused on the validation of the test procedure for the quantitative determination of bifenthrin contents in the emulsifiable concentrate and measurement of uncertainty. The purpose of this validation procedure is to demonstrate that it is suitable for the intended use. This was determined by gas chromatography with a flame ionization detector (FID). The estimation was carried out on Shimadzu GC equipped with TRB-5 (95% dimethyl, 5% diphenyl polysiloxane) column using a nitrogen carrier gas.

Results

Different parameters of validation (precision, accuracy, linearity, specificity, selectivity, and robustness) were executed. All steps of method validation were performed, and its uncertainty is determined. The method is simple, selective, accurate, precise, cost-effective, and suitable. The validation parameters are based on harmonized guidelines on the validation of the analytical test method.

Conclusions

Pesticide formulation bodies can use this method for the qualitative and quantitative determination of bifenthrin different formulations. These data verify that the method is validated, and all results are in an acceptable limit. The method is developed on GC. Moreover, the analysis time is also short as compared to that of HPLC. The developed method is simple reliable and has a realistic approach.