Microextraction of organophosphorus pesticides from tea samples with di-(2-ethylhexyl) phosphoric acid based supramolecular solvent

In this work, a new supramolecular solvent (SUPRAS) was prepared using di-(2-ethylhexyl) phosphoric acid, and its feasibility was investigated for the microextraction of organophosphorus pesticides from tea drinks. Fenitrothion, phosalone, and chlorpyrifos were chosen as model organophosphorus pesticides due to their widespread use in agricultural production. The SUPRAS-based microextraction method was then combined with high-performance liquid chromatography-ultraviolet detection (HPLC-UV) for the simultaneous separation and analysis of extracted analytes. The sample preparation method was based on the extraction of analytes into the spontaneously formed SUPRAS phase in a ternary mixture consisting of di-(2-ethylhexyl) phosphoric acid, tetrahydrofuran and aqueous sample. A phase diagram showing the boundaries of the SUPRAS region was created, and the shape, size and structural properties of the coacervate droplets in the SUPRAS phase were investigated using an optical microscope. Some parameters affecting the performance of the extraction method including the volume of di-(2-ethylhexyl) phosphoric acid, volume of tetrahydrofuran, ionic strength, and extraction time were thoroughly investigated and optimized. Under optimized conditions, extraction efficiencies and enrichment factors were obtained in the range of 77–98 and 15–19%, respectively. The calibration plots were linear over the concentration range of 25–1000 μg/L with coefficients of determination greater than 0.9994 for all pesticides. Moreover, low limits of detection (6–10 μg/L) and good reproducibility (<9.5 %) were achieved for the target analytes. Finally, the proposed method was successfully applied to the analysis of different tea samples, and the relative recoveries of organophosphorus pesticides from the spiked samples were found to be in the range of 82–106 %.