HPLC/MS of Antibiotics in Biological Samples

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We analyzed two representative antibiotics, cephems and aminoglycosides, by our recently established system of capillary high-performance liquid chromatography (HPLC)/fast atom bombardment (FAB)-mass spectrometry (MS). Cephems could be analyzed by conventional reversed-phase HPLC, but aminoglycosides required ion-pair reversed-phase HPLC.As a matrix for FAB-MS, diethanolamine (DEA) along with glycerin (GLY) were used. The authentic compounds of 24 cephems and 8 aminoglycosides were analyzed by our capillary HPLC/FAB-MS system. Whend a suitable matrix was used for each antibiotic, quasi-molecular peak together with adequate fragment peaks were obtained from all 32 antibiotics, though DEA provided more information on molecular mass of a compound than did GLY for some cephems. The range of the detection limits of the mass spectral measurements was rather wide (10 ng - 2.5 mug on column), but sufficiently sensitive to detect therapeutic levels of antibiotics in human serum for most compounds under investigation.The extraction of the antibiotics from human serum was studied using solid-phase extraction cartridges. In general, Bond Elut C_<18> cartridges were effective for the isolation of cephems and aminoglycosides under investigation. With this isolation procedure and the capillary HPLC/FAB-MS in the positive mode, cefazolin and ribostamycin, representative cephem antibiotic and aminoglycoside, respectively, could be identified in sera from cadavers who suddenly died after injection of them. The capillary HPLCIFAB-MS was semi-quantitative for all compounds under investigation. However, we believe that accurate quantifation can be made by SIM of FAB-MS with a suitable isotopic internal standard. We also devised a simple method for quantitation of some other drugs in human serum by UV monitoring of the capillary HPLC.These analytical methods devised in this study would seem to be useful in clinical pharmacology as well as in forensic toxicology.