Analysis of beta-lactam antibiotics by high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry using bromoform.

The novel identification method for a heat-unstable antibiotic, FC/TA-891 and its active metabolite (FCE22101) by high-performance liquid chromatography (HPLC)-atmospheric pressure chemical ionization mass spectrometry (APCI-MS) employing bromoform as an ionization acceleration solvent, was applied to eight penicillins and 13 cephalosporins which are groups of beta-lactam antibiotics. The conditions of HPLC-APCI-MS were examined with ampicillin. Bromoform or chloroform was added to the mobile phase in HPLC to compare the difference between bromine and chlorine adducted ions. For all penicillins except sulbenicillin, both chlorine adducted and bromine adducted ions were observed with a flow injection method. The results indicated that the relative sensitivity ratios of bromine adducted ions to [M-H](-) were higher than those of chlorine adducted ions. These bromine adduct ions could be clearly distinguished from other ions due to its isotopical ratio (1:1), leading to an easy identification of the compounds. For 13 cephalosporins, bromine adducted ions were detected in nine compounds, and chlorine adducted ions were detected in four compounds. The separation of four antibiotics was investigated with an HPLC column to apply this technique to the actual analysis. The capability was equal as in the flow injection method and it found that this technique, i.e. APCI-MS with bromoform could be applicable in the separation analysis.