Study On The CID-induced Decomposition Mechanisms Of Azlocillin And Piperacillin By Using Electrospray Lonization Mass Spectrometry

In the present dissertation, antibiotics with β-lactam ring or penicillins are investigated using electrospray ionization source combined with triple-quadrupole-time-of-flight mass spectrometry, and the structures and collision-induced fragmentation pathways of the molecules are analyzed. In the last chapter, the low-temperature oxidation instrument designed by our group is introduced and quantitative analysis on dimethyl ether is carried out.In the first chapter, the arising, development outline, application prospect of mass spectrometer, and particularly its principles and components are briefly introduced. Important parameters such as resolution, mass range, sensitivity and accuracy are discussed. The advantages and disadvantages of several different ionization methods are evaluated, and electrospray ionization source, single quadruple mass analyzers, time-of-flight mass analyzer and ion detector used in the present work are described in detail.In the second chapter, the main experimental instrument Q-star pulsar I produced by SCIEX and its operation mode, usage, ion pathways, as well as related pneumatic system, circuit system and vacuum equipment are elaborated. Then the components and characteristics of the electrospray ionization source designed by our group are analyzed. Calculation method within density functional theory (PM3) involved in the present study is explained in detail, and subsequent theoretical analysis is based on the calculated zero point energy of the reactants, products, intermediates and transition states.In the third chapter which is the heart of this work, the collision induced fragmentation pathways of two kinds of penicillin drug molecules, azlocillin and piperacillin, are discussed. Electrospray ionization as a "soft" ionization technique is widely used in polar compounds, volatile compounds and thermally unstable compounds, and thus suitable for drug molecule research. For the molecular properties of azlocillin and piperacillin. the pseudo-molecule-ion intensities of the parent ions and the mass spectrograms under different collision energies are obtained, and then the parent signal intensities with different collision energies are analyzed. Finally the corresponding fragmentation pathways of fragment ions are analyzed and the analytes are compared. According to theoretical calculation, β-lactam ring as well as thiazolidine ring connecting with P-lactam ring tends to open. The fragmentation pathways of such drug molecules are summarized based on experimental data and calculation results, providing theoretical basis for body metabolism and environmental degradation.The forth chapter is an introduction of low-temperature oxidation instrument designed by our group. As oxidation, pyrolysis, and premixed flame burning are several ways to study combustion kinetics model, it is of vital role to study low-temperature oxidation. In general, oxidation process is sensitive to temperature, and long-chain ester, aromatics with long branched chain have obvious negative temperature areas. Flow tube has advantages such as structure simplicity, easy setting of reaction time and pressure, stability of gas-flowing process, and the procedure of designing flow tube low-temperature oxidation instrument is presented in detail, from material selection, residence time calculation, size selection of the tube to external device assembly, designing of pneumatic system and vacuum system. At last, the low-temperature oxidation process of dimethyl ether is tested with gas chromatography mass spectrometry.