RESUMEN
A method for the detection of nortestosterone (NT) in bovine muscle at levels below 1 microgram/kg is described, based on enzymatic digestion of the sample, clean-up by immunoaffinity chromatography after defatting and detection by gas chromatography-mass spectrometry (selected-ion monitoring). The immunoaffinity matrix was prepared after combining the isolated immunoglobulin G fractions from a rabbit antiserum raised against NT and methyltestosterone (MT). Its capacity per millilitre of gel was approximately 10 ng for each of the two steroids. Results for samples containing 0.1 microgram/kg NT and above are described. It is concluded that for multi-residue analysis of samples of muscle at levels as low as 0.1 microgram/kg, multi-immunoaffinity chromatography is a very suitable method of sample clean-up. For purposes of quantification the trideuterated internal standard [16,16,17 alpha-2H3] nortestosterone was synthesized.