Enzymatic-microwave assisted extraction and high-performance liquid chromatography–mass spectrometry for the determination of selected veterinary antibiotics in fish and mussel samples

A new method based on enzymatic-microwave assisted extraction prior to high performance liquid chromatography (HPLC) has been developed for the determination of 11 antibiotics (drugs) and the main metabolites of five of them in fish tissue and mussel samples. The analysed compounds were sulfadiazine (SDI), N 4-acetylsulfadiazine (NDI), sulfamethazine (SMZ), N 4-acetylsulfamethazine (NMZ), sulfamerazine (SMR), N 4-acetylsulfamerazine (NMR), sulfamethoxazole (SMX), trimetroprim (TMP), amoxicillin (AMX), amoxicilloic acid (AMA), ampicillin (AMP), ampicilloic acid (APA), chloramphenicol (CLF), thiamphenicol (TIF), oxytetracycline (OXT) and chlortetracycline (CLT). The main factors affecting the extraction efficiency were optimized in tissue of hake ( Merluccius merluccius), anchovy ( Engraulis encrasicolus), mussel ( Mytilus sp.) and wedge sole ( Solea solea). The microwave extraction was carried out using an extraction time of 5 min with 5 mL of water at 50 W and posterior clean up with dichloromethane. High-performance liquid chromatography (HPLC)–mass spectrometry was used for the determination of the antibiotics. The separation of the analysed compounds was conducted by means of a Phenomenex ® Gemini C 18 (150 mm × 4.6 mm I.D., particle size 5 μm) analytical column with LiChroCART ® LiChrospher ® C 18 (4 mm × 4 mm, particle size 5 μm) guard-column. Analysed drugs were determined using formic acid 0.1% in water and acetonitrile in gradient elution mode as mobile phase. Under the optimal conditions, the average recoveries of all the analysed drugs were in the range 70–100%. The proposed method was applied to samples obtained from Mediterranean sea and also evaluated by a laboratory assay consisting in the determination of the targeted analytes in samples of Cyprinus carpio that had been previously administered the antibiotics.