Development of a Green and Rapid Emulsive Liquid–Liquid Microextraction Method for Organophosphate Insecticides

This study presents a rapid method for detecting organophosphate insecticide residues using emulsive liquid–liquid microextraction combined with ultraviolet spectrophotometry (ELLME-UV). By employing the conductor-like screening model for real solvents to predict the chemical potentials of 17 extractants, oleic acid was identified as the optimal extractant owing to its high binding affinity, eliminating the need for trial-and-error selection. In the ELLME-UV process, an oil-in-water emulsion was formed by combining oleic acid with an aqueous alkaline solution, followed by sample addition, allowing rapid extraction within 1 min. Then, citric acid was added to induce rapid demulsification and separate oleic acid from the sample within 10 s, eliminating the need for a time-consuming centrifugation step. Under alkaline conditions, p-nitrophenol, prepared from parathion-methyl, exhibited a strong UV signal, and it was efficiently transferred to the separated oleic acid phase, enabling its detection in a 96-well plate within 1 min. Using pH adjustment, oleic acid was successfully used as an extractant, achieving emulsification and demulsification in the sample. By integrating extraction and derivatization into a single step, the proposed method simplifies sample pretreatment and detection, increasing the overall efficiency. The ELLME-UV method was successfully applied to various matrices, and recoveries ranged from 85.3 to 102.9%, with relative standard deviations of 0.6–4.5%, demonstrating its accuracy and reproducibility. These results highlight the potential of the proposed method as a rapid, simple, and environmentally sustainable solution for detecting organophosphate insecticide residues. This study highlights the environmentally friendly properties of oleic acid, which has historically been difficult to emulsify.