CapillaryZone Electrophoresis Determination of Oxytetracycline in Pig TissueSamples at Maximum Residue Limits 2001,54,355-359 M. Herndndez* / F. Borrull / M. Calull Departament de Quimica Analitica i Quimica Orgdmica, Universitat Rovira i Virgili, R Imperial Tdrraco 1,43005 Tarragona, Spain; E-Maih socias@q uimica.u rv.es Key Words Capillary zone electrophoresis Solid-phase extraction Oxytetracychne Tissue samples Summary The determination of the antibiotic oxytetracycline (OTC), in pig tissues was investigated by ca- pillaryzone electrophoresis (CZE) with a prior solicl-phase extraction (SPE)using alkyl-boncled silica and polymeric cartridges. The methodology developed allows determination of OTC in pig kidney, liver and muscle samples with detection limits below maximum residue hmitvalues, and the procedures to extract OTC and clean-up the matrix are simple and reliable. The limit of detection for OTC was 160, 120 and 85 ~g kg 1 for kidney, liver and muscle samples, re- spectively The average recoveries from spiked samples (200 I~g kg 1 and 1600 I~g kg 1) were in excess of 63% with coefficients of variation bel',,veen 2.0 and 9.8%. This method would be useful for routine monitoring of oxytetracychne residues in pig tissues. Introduction Tetracyclines (TCs) are broad-spectrum antibacterial compounds commonly used in the prevention and treatment of dis- eases in livestock [1]. Therefore, monitor- ing of residual TCs is important from the viewpoint of veterinary food hygiene. The residues of the drugs may remain in tis- sues, milk, etc. intended for human con- sumption. To prevent health problems with consumers, maximum residue limits (MRL) of these compounds and other drugs in livestock products have been es- tablished. MRL are the maximum con- centrations of residues resulting from the use of a veterinary drug (expressed in mg kg 1 or ixg kg 1 on a fresh weight basis) that the European Union (EU) permits or recognizes as acceptable in or on a food [2]. Oxytetracycline (OTC) is the tetracy- cline antibiotic most frequently used. MRL values are fixed for this compound in some tissues from pigs, poultry and sheep. MRL values for OTC in pig tissue samples are shown in Table I. Conse- quently, one requirement of the analytical methods used to determine OTC residues in tissue samples is that they have detec- tion limits below the MRL values. A number of analytical methods for determining OTC by high-performance li- quid chromatography technique (HPLC) in animal products have been published [3 16], e.g. the determination of OTC in milk samples [5, 8, 9], in plasma and / or urine samples [4] and in tissue samples [4, 6, 7, 10 16]. There are a few papers in which OTC has been determined in biolo- gical samples by capillary electrophoresis (CE) [17 19]. For instance, Huang et al. [17] determined OTC residues in raw and cooked channel fish by CE, and samples were previous deproteinizated with tri- chloroacetic acid (TCA), as a clean-up step. In other studies the determination of several TCs in plasma [18, 19] and milk samples [18] have been developed. CE has many advantages over HPLC for the analysis of OTC, such as the diffi- culties associated with peak tailing and low efficiency in HPLC due to interaction with the residual silanol groups on silica- based packing materials. CE has also the advantages of shorter analysis time and small consumption of sample and solvent in comparison with HPLC. OTC has been efficiently separated by capillary zone electrophoresis (CZE) using different buf- fer systems, such as sodium phosphate EDTA, sodium carbonate EDTA and sodium borate EDTA [20 23]. Table I. MRL values of OTC fixed in tissue samples. Pig samples Target tissue MRL values (~tgOTC/kg tissue) Kidney 600 Liver 300 Muscle 100 Original 0009-5893/00/02 Chromatographia 2001, 54, September (No. 5/6) 355- 05 $ 03.00/0 9 2001 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH 355