Determination of lincomycin residues in salmon tissues by gas chromatography with nitrogen-phosphorus detection

A sensitive method for the determination of lincomycin residues in fish tissues is described. Lincomycin was extracted from fish tissues with phosphate buffer (pH 4.5). The extract was concentrated with a C18 solid-phase extraction cartridge and further cleaned up by solvent extraction. Lincomycin was derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide to form a trimethylsilyl derivative before being analyzed by gas chromatography with nitrogen-phosphorus detection. Coumaphos was used as the internal standard. Assays showed good linearity in the range 25-250 ppb (ng/g) (r = 0.9994). Recoveries of fortified lincomycin at 50, 100 and 200 ppb were > 80% with relative standard deviations < 6%. The limit of detection of the method was 1.7 ppb and the limit of quantitation was 3.8 ppb.