Preparation of molecularly imprinted polymer coatings based on via a sandwich method for solid-phase microextraction of 2,4-dichlorophenoxyacetic acid from milk

This study proposes new molecularly imprinted solid-phase microextraction (MIP-SPME) coatings based on a sandwich method for the extraction of 2,4-dichlorophenoxyacetic acid (2,4-D) from milk samples. MIP-SPME coatings were prepared by sandwich surface polymerization, using 2,4-dichlorophenoxyacetic acid (2,4-D) as the template, 4-vinylpyridine as the functional monomer and PTFE membrane as supporting material. MIP-SPME coatings were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, Brunner Emmet Teller measurements and adsorption experiments. The adsorption capacities of nonimprinted polymer solid-phase microextraction and MIP-SPME coatings were 41.8 mg/g and 31.8 mg/g, respectively. Regeneration adsorption was achieved in 137 runs (relative standard deviation, RSD <= 6.35%) with an indication of high stability and reusability. The parameters, such as loading solvent, time and washing and elution solvents were optimized and found to be methanol-water (1/9, v/v), 1 h, water and acetonitrile-methanol (1/9, v/v), respectively. Under the optimized conditions, the developed SPME method was successfully applied for the selective extraction and determination of 2,4-D in milk samples coupled with HPLC, with a recovery of 88.8-96.6% (RSD <= 5.1%). The limits of determination and the limits of quantitation were found to be 0.03 and 0.1 mg L-1, respectively.