Determination of ractopamine and clenbuterol in feeds by gas chromatography–mass spectrometry

A simple, sensitive and reproducible gas chromatographic–mass spectrometric method was developed for monitoring ractopamine (RAC) and clenbuterol (CLB) in feeds. Feed samples were extracted with 0.1 M perchloric acid, centrifuged, neutralized, followed by liquid–liquid extraction with ethyl acetate-isopropanol (9:1, v/v). The concentrated extracts were dissolved in 0.02 M NH₄Ac (pH 5.2), and applied to a solid phase extraction SCX cartridge for cleanup. The drugs were eluted with 3% (v/v) ammonia hydroxide in methanol, and the eluate was evaporated to dryness. The residue was derivatized with N,O-bis (trimethylsilyl) trifluoroacetamide at 80 °C for 1 h, and cooled, then analyzed by gas chromatography–mass spectrometry. The selected ions monitoring mode was performed at m/z 179, 250, 267 and 502 for RAC, and m/z 86, 243, 262 and 277 for CLB. Recoveries of RAC and CLB from concentrated feeds and premix fortified at 10, 100 and 5000 μg/kg were between 64.6 and 84.2%, with relative standard deviations of less than 15%. The limits of detection were about 4 μg/kg for RAC and 2 μg/kg for CLB.