Use of metal chelate affinity chromatography and membrane-based ion-exchange as clean-up procedure for trace residue analysis of tetracyclines in animal tissues and egg.

A new and efficient procedure for the clean-up of tetracycline residues in animal tissues and egg prior to reversed-phase high-performance liquid chromatography is described. The principal steps involve homogenization of the tissues in sodium succinate buffer and methanol, followed by centrifugation and clean-up with metal chelate affinity chromatography (MCAC). After further concentration on an Empore extraction membrane with cation-exchange properties, the sample is analysed by HPLC with fluorescence detection. The method was tested on porcine kidney and muscle, bovine liver and whole chicken's egg. The recoveries were determined from spiked tissues for oxytetracycline, tetracycline, chlortetracycline and doxycycline and ranged from 40 to 70%, with repeatabilities below 10% R.S.D.. The analytical responses were linear in the range up to at least 1000 ng/g. The detection limits of the method were estimated at 0.42 ng/g of oxytetracycline, 0.49 ng/g of tetracycline, 0.66 ng/g of chlortetracycline and 1.38 ng/g of doxycycline in porcine muscle, using signal-to-noise ratios of 4:1. Similar detection limits were estimated for kidney, liver and egg. The measured limits of quantification were 2 ng/g for oxytetracycline, 3 ng/g for tetracycline, 4 ng/g for chlortetracycline and 5 ng/g for doxycycline in porcine kidney. The advantage of this method over existing methods is its increased limit of detection.