Kazhal Khazaei, Shahram Seidi, Mahsa Shirkhodaie, Sara Bakhshmaleki
A novel, and efficient spin-assisted dispersive micro-solid phase extraction (SA-DµSPE) method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for quantifying trace levels of organophosphorus pesticide (OPP) residues in plant-based milk alternatives (PBMAs). To fabricate the extraction sorbent, silica-coated magnetite nanoparticles were incorporated into a copper-based metal-organic gel (MOG) network, followed by freeze-drying, yielding a porous magnetic aerogel with excellent adsorption properties. A custom-built electrical device was employed to promote sorbent dispersion and expedite its magnetic separation. Adsorption and desorption parameters were optimized using a rotatable central composite design (RCCD) and one-variable-at-a-time (OVAT) approach. Matrix effect (ME%) values ranged from 15.0% to 34.9%; therefore, a matrix-matched calibration method was employed for OPP quantification. Under the optimal conditions, calibration curves in various matrices were linear within the range of 0.05-200.0 ng mL-1, with coefficients of determination (R²) ≥ 0.9978. Limits of detection (LODs) and quantification (LOQs) ranged from 0.03 to 0.08 ng mL-1 and 0.05 to 0.25 ng mL⁻¹, respectively. Preconcentration factors (PFs) were calculated in the range of 16.3 to 24.3 for different matrices, corresponding to absolute extraction recoveries (ER%) between 40.8% and 60.8%. The method provided relative recoveries (RR%s) of 90.0%-111.3% and relative standard deviations (RSD%) of 3.5-6.8% for the determination of OPPs in almond, soy, and hazelnut milks. The newly prepared aerogel combined with LC-MS/MS provided efficient retention of the target analytes, which, together with the other analytical figures of merit, confirms the proposed method as a suitable alternative for OPP determination in PBMAs.