DETERMINATION OF TRIMETHOPRIM IN TISSUES USING LIQUID-CHROMATOGRAPHY THERMOSPRAY MASS-SPECTROMETRY

A method is described for the determination of the antibacterial drug trimethoprim in tissues. Minced tissue is homogenised with chloroform- acetone (1 + 1 v/v), filtered, and the filtrate evaporated to an oily residue using a rotary evaporator, The residue is redissolved in metha nol-water-acetic acid (50 + 48.7 + 1.3 v/v) and any fats present are p artitioned into hexane, The aqueous phase is analysed by liquid chroma tography-thermospray mass spectrometry in positive mode with the proto nated molecular ion at m/z 291 being monitored. Recoveries ranged betw een 60% in liver and 79% in muscle. The limit of determination was 25 mu g kg(-1) and the limit of detection was approximately 4 mu g kg(-1) . The method is suitable for monitoring tissues taken under national s urveillance schemes for veterinary drug residues.