Magnetic molecularly imprinted polymers for the detection of aminopyralid in milk using dispersive solid-phase extraction†
A method for dummy molecular imprinting-magnetic dispersive solid-phase extraction (MI-MDSPE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the selective determination of aminopyralid in milk. The magnetic material and polymers were combined via a series of modifications in Fe3O4. Fe3O4@SiO2–NH2@MIP, Fe3O4@SiO2–COOH@MIP and two types of aminopyralid-specific magnetic molecularly imprinted polymers (MMIPs) were prepared on the surface of magnetic nanoparticles modified with amino and carboxyl groups. The morphology and magnetic properties of the polymer were characterized. Fe3O4@SiO2–NH2@MIP exhibits not only good dispersibility and magnetic properties, but also an outstanding recognition pattern to the target analyte. Adsorption experiments demonstrated that Fe3O4@SiO2–NH2@MIP, with a high specific surface area and fast mass transfer rate, had a higher affinity than Fe3O4@SiO2–COOH@MIP towards aminopyralid. Under the optimized MI-MDSPE conditions, the method had good linearity (R2 > 0.9972), excellent recoveries (83.3–90%), and good precision (relative standard deviations (RSDs) < 12.6%). This method has limits of detection (LOD) and quantification (LOQ) of 0.231 and 0.77 μg kg−1, respectively, indicating that these MMIPs can be used to analyse trace levels of aminopyralid in real samples.