Research On Analysis Of The Antibiotics By Electrospray Ionization Mass Spectrometry

Electrospray ionization mass spectrometry (ESI-MS) is a "soft" ionizationtechnique. It can be used under conditions of atmospheric pressure and large quantitiesof solvents to analyze polar compounds, volatile compounds or thermal unstablecompounds, such as drugs and their metabolites, natural product, biomacromolecules,ect.ESI-MS has many advantages.such as simple operation, less sample consumption,and no tedious pre-process. This paper use ESI-MS for the analysis of penicillins,cephalosporins and quinolones. The structure and stability test in different solvents ofthe three kinds of antibiotics were analyzed through obtaining accurate mass andelements of compounds, fragmentation ion mass and structural information, as well asD-labeling experiments.Different structural types of antibiotics have been analyzed systematically usingelectrospray ionization high-resolution mass spectrometry. In both positive-andnegative-ion modes the penicillins, cephalosporins and quinolones fragmentationmechanisms were analysed, including precursor protonated, sodiated molecules anddeprotonated ions which provideing many complementary informative product ions.This paper use isotope labeling method to study the fragmentation pathways ofampicillin, sultamicillin, cephradine, and cefaclor. By detecting molecular ion peak of[M+D]~+,[M/D+Na]~+and [M-D]~-as well as their characteristic cleavage fragments,confirmed the fragmentation pathways of the antibiotics. The fragmentation pathwaysof these drugs provide a theoretical basis for their mass spectrometry analysis, bodymetabolism or environmental degradation products.This paper analyzed the stabilities of three kind of antibiotics in methanol, aceticacid (pH5-6), hydrochloric acid (pH3-4) and sodium hydroxide (pH9-10). Experimentalresults found that penicillins and cephalosporins were easy to react in methanol and acidor alkaline solution. And then, the structure of the main reaction products were analyzed.Quinolones were stable because their molecular structures form conjugated π bond, onlychange in norfloxacin and lomefloxacin were observed, that is carboxyl of the structureoccurred react in alkaline solution. In addition, mass spectrogram of quinolones wereusually observed precursor protonated, but in alkaline solution obtained sodiated molecules, these provides simple and effective analytical methods for the study ofantibiotic stability.