We aim to develop a solid-phase extraction (SPE) based on a dummy molecularly imprinted polymer (MIP) and liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS) for selective determination of four pyridine carboxylic acid herbicides (aminopyralid, picloram, fluroxypyr, and clopyralid) in milk samples. Using picloram as the dummy template, MIP nanocomposites with highly selective recognition and adsorption for the target molecule and its structural analogs were successfully synthesized by precipitation polymerization. Adsorption isotherms and kinetics were used to determine the adsorption performance and specific recognition mechanism of both MIPs and non-molecularly imprinted polymers (NIP). The Scatchard plot analysis revealed that two different binding sites were formed in the MIP with maximum binding capacity (Qmax) of 1171.8 μg·g-1 and 3022.5 μg·g-1, respectively. Recovery at three spiking levels of 10, 20, and 50 μg·L-1 ranged between 75.3 and 89.8% with relative standard deviations (RSDs) <14.3%.The limit of detection (LOD) was estimated to be 0.124 μg·L-1. Finally, the feasibility of the proposed methodology was successfully applied to quantify aminopyralid and another three pyridine carboxylic acid herbicides in milk.
Keywords: Milk; Molecularly imprinted polymers; Pyridine carboxylic acid herbicides; Residue determination; Solid-phase extraction.
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