Development of COF@MOF Nanocomposite-Based Dispersive Solid-Phase Microextraction for the Extraction of Pesticides from Strawberries

A dispersive solid-phase extraction approach was developed for extracting certain pesticides from strawberry samples. This method was combined with dispersive liquid–liquid microextraction to further enrich the samples. To achieve this, 5 mg of the synthesized nanocomposite was used for the extraction of the analytes from 5 mL of the sample solution under agitation by vortexing for 8 min. After centrifugation (at 5000 rpm for 3 min), the supernatant was removed. Then, the adsorbed analytes were eluted with 1.0 mL of ethanol using ultrasonication. The mixture was then centrifuged at 5000 rpm for 3 min, and the eluent was transferred into another microtube and mixed with 80 µL of chloroform. The mixture was aspirated into a syringe and then rapidly injected into 5-mL sodium chloride solution (4%, w/v). The resulting cloudy solution was centrifuged and 1 µL of the settled phase was used in the analysis step. The validity of the method was assessed after optimizing the experimental conditions. The obtained results showed that the limits of detection (LOD) and quantification (LOQ) for the analytes were in the ranges of 0.08–0.48 and 0.29–1.4 ng mL⁻¹, respectively. The calibration graphs were linear in the range of 1.4–3000 ng mL⁻¹ with a coefficient of determination (r²) ≥ 0.991. The relative standard deviations (RSDs) for replicate analyses were ≤ 5.2%. The enrichment factors (EFs) and extraction recoveries (ERs) for the studied analytes were in the ranges of 365–405 and 73–81%, respectively. The developed method was performed on several strawberry samples and the results showed that the samples were free of the studied pesticides.