Gas chromatographic-mass spectrometric detection and quantitation of lincomycin in animal feedingstuffs

A substantially improved assay was developed for lincomycin A in animal feedingstuffs. The assay allows unambiguous quantitation of at least 0.1 ppm in feed. Lincomycin B did not interfere because of differences in both retention time and mass of the main fragment ion in electron impact (EI) spectra. The assay using single ion monitoring with EI detection would not discriminate between lincomycin A and clindamycin. The presence of the latter was easily confirmed by using gas chromatography-mass spectrometry in the chemical ionization mode. The assay for lincomycin A was linear in the range 0-40 ng applied to the gas chromatographic column. The recovery was 93.4 +/- 4.2% at 1 and 5 ppm and 86.2 +/- 5.5% at 0.1 ppm in feed. The coefficient of variation of the assay was 4.8% at both 1 and 5 ppm, and was 6.43% at 0.1 ppm.