A novel, sensitive, high performance liquid chromatography/tandem mass spectrometric (i.e. mass spectrometry/mass spectrometry) method with on-line extraction and clean-up for the screening and confirmation of residues of tetracyclines in kidney has been developed. After liquid extraction of homogenised kidney with McIlvain buffer, an aliquot of the extract is directly injected on the LC/MS/MS system with further extraction and clean-up of the sample on-line. Detection of the analytes was achieved by positive electrospray ionization followed by multiple reaction monitoring. For each tetracycline the collisional decomposition of the protonated molecule to a unique, abundant fragment ion was monitored. The method has been validated for tetracycline, oxytetracycline, chlortetracycline and doxycycline. Calibration curves resulting from spiked blank kidney samples at the 100-1200 microgram/kg level showed good linear correlation. At the level of 600 microgram/kg both within- and between-day precision, as measured by relative standard deviation (RSD), were less than 7%. The limits of detection (LODs) for tetracycline, oxytetracycline, chlortetracycline and doxycyline were 18, 23, 24 and 21 microgram/kg, respectively. The limits of quantification (LOQs) for tetracycline, oxytetracycline, chlortetracycline and doxycyline were 36, 46, 47 and 42 microgram/kg, respectively. The recoveries ranged from 71 to 91%. The procedure provides a rapid, reliable and sensitive method for the determination of residues of tetracyclines in bovine kidney. The advantage of this method over existing methods is its decreased sample preparation and analysis time, which makes the method more suitable for routine analysis.

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