Determination of gentamicin after trimethylsilylimidazole and trifluoroacetic anhydride derivatization using gas chromatography and negative ion chemical ionization ion trap mass spectrometry

Abstract

A gas chromatographic method for the determination of gentamicin, an aminoglycoside antibiotic, was developed. A two step derivatization method utilizing trimethylsilylimidazole for silylation of the hydroxyl groups and trifluoroacetic anhydride for acetylation of the amino groups was used. Chemical ionization and negative ion monitoring resulted in greatly improved sensitivity and more informative fragmentation of the gentamicin components compared with electron ionization and positive ion monitoring. Tandem mass spectrometry was used for the identification of the gentamicin components and for characterization of the derivatized groups. The optimized method also allowed the use of three ions for selected ion monitoring. The method significantly improved the determination of gentamicin compared with previously described gas chromatographic methods. Chemical ionization and negative ion monitoring with the use of an ion trap analyzer appeared superior to other detection modes.