Multiresidue analysis of cephalosporin antibiotics in bovine milk based on molecularly imprinted polymer extraction followed by liquid chromatography-tandem mass spectrometry

- A MIP able to recognize six cephalosporins simultaneously has been developed.
- A novel cephalosporins' surrogate was designed and prepared for the MIP synthesis.
- Tuning of the polymer composition has led to porous MIP microbeads for fast SPE.
- A MISPE-UHPLC-MS/MS method was developed to analyze the antibiotics in raw milk.
- Detection limits are well below the MRLs set by the European Union legislation.

This work reports the preparation of molecularly imprinted polymers (MIPs) selective to cephalosporin (CF) antibiotics, and their application as molecularly imprinted solid-phase extraction (MISPE) sorbents for the determination of these antimicrobials in milk samples. Several functional monomers and cross-linkers have been screened to select the best combination that provides high selectivity for the simultaneous multiresidue extraction of cefthiofur (THIO), cefazolin (AZO), cefquinome (QUI), cephapirin (API), cephalexin (ALE) and cephalonium (ALO) from the samples. The novel MIPs were prepared by a non-covalent imprinting approach in the form of spherical microparticles using the synthetic surrogate molecule sodium 7-(2-biphenylylcarboxamido)-3-methyl-3-cepheme-4-carboxylate, N-3,5-bis(trifluoromethyl)phenyl-N′-4-vinylphenyl urea (VPU) as functional monomer, and divinylbenzene (DVB) as crosslinking agent in a 1:2:20 molar ratio. The optimized MISPE method allowed the extraction of the target antimicrobials from raw cow milk samples using a selective washing with 5 mL methanol/2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) buffer (0.1 M, pH 7.5) (2:98, v/v) to remove the non-specifically retained compounds, followed by elution with 1 mL of trifluoroacetic acid (TFA) in methanol (0.1:99.9, v/v). The extracts have been analysed by UHPLC-MS/MS and the analytical method has been validated according to EU guideline 2002/657/EC. The limits of quantification (S/N = 10) were in the 1.7-12.5 μg kg−1 range, well below the maximum residue limits (MRLs) currently established for the quantified cephalosporins in milk samples. The developed MIP allows mutiresidual determination of the six cephalosporin antibiotics mentioned above, significantly broadening the application to food analysis of MISPE methods.