Molecularly imprinted polymers and HPLC-MS/MS for determining penicillins in infant formulas

The β-lactams are among the most widely used anti-microbial drugs in veterinary medicine, including the penicillins and the cephalosporins. The dairy cattle may suffer from respiratory and digestive infections very often, but the inflammation of the mammary gland is very problematic for the farmer. Mastitis, although an animal welfare problem, is a big economic problem because it increases the somatic cell count, a milk quality indicator. These infections are frequently treated with penicillins, one of the most applied drugs in dairy cattle. However, the incorrect use of these antibiotics may result in the presence of residues in food and represents a potential risk for consumers. To avoid health risks for the consumer due to residues, the EU has defined safe maximum residue limits (MRL) through Commission Regulation (EU) No. 37/2010. On the other hand, the presence of residues in milk may lead to their presence also in dairy products, such as milk powder and/or infant formulas. Although LC–MS is a trustful option for confirmation and quantification of antibiotics, the analysis of real samples with complex matrices usually implies previous clean-up steps using common solid-phase extraction procedures. The main drawback of this extraction technique is the lack of selectivity of the sorbents. Molecularly imprinted polymers (MIP) are synthetic materials with recognition sites that specifically bind target molecules in mixtures with other compounds. The aim of the present work is to test the suitability of various MIP, synthesized using different templates and cross-linker monomers, for the simultaneous extraction of eight penicillins (ampicillin, amoxicillin, oxacillin, penicillin G, penicillin V, cloxacillin, dicloxacillin and nafcillin). The detection was performed using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and the applicability of these polymers as sorbents for the extraction of penicillins at the level of interest (MRLs) in infant formulas was proved.