Green deep eutectic solvent-enabled rapid detection of edible oil adulteration via capsaicinoids: experimental and density functional theory studies

To address the technical challenges in detecting edible oil adulteration, this study developed a series of green deep eutectic solvents (DESs) by combining tetrabutylammonium chloride (TBAC), tetrabutylammonium bromide (TBAB), and choline chloride (ChCl) with acetic acid (AcOH). These DESs were innovatively coupled with liquid-liquid microextraction (LLME) technology to establish a rapid and sustainable method for identifying adulterated edible oils. Critical parameters were methodically evaluated, including DES composition, solvent volume, and extraction time. The results indicated that TBAC-AcOH (molar ratio 1:2) DES exhibited the best extraction ability, the optimal extractant dosage was 120 μL and the extraction time was 3 min. Under the optimized experimental conditions, the proposed method showed a good linearity (R 2  ≥ 0.998), the spiked recoveries in real oil samples ranged from 85.1% to 98.2%, with relative standard deviation (RSD) ≤ 3.5%. The constitution of the DES was verified by nuclear magnetic resonance ( 1 H NMR), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), and differential scanning calorimetry (DSC). Mechanistic investigations via theoretical calculations revealed that DESs primarily extract nonivamide and dihydrocapsaicin through hydrogen bonding interactions. This method provides a convenient, novel and green strategy for the identification of capsaicinoids in edible oil adulteration or illegal addition.