岛津GCMS-TQ8040教材说课.ppt

This is the example of EI spectra. The upper is for Benzene. The base peak is the molecular ion 78 The lower is for Acetone The base peak is the fragment ion 43 The next is the chemical ionization method In CI, reagent gas is required for ionization. Since CI can be occurred at more than about 10Pa of ion source pressure, the ion source is closed type . The feature of CI is the ionization with less fragmentation, we call such an ionization “ soft ionization”. In the CI ，pseudo -molecular ions tend to be generated. The pseudo-molecular ion is the ion such that a proton ion H+ is added to sample molecule. So the mass number of pseudo-molecular ion is the mass number of sample molecule +1 Thus CI is effective for determination of molecular weight. These are the spectra of Methylstearate for EI and CI The molecular weight of this compound is 298. EI spectrum shows existence of many fragment ions . On the other hand , CI spectrum clearly shows pseudo-molecular ions at m/z 299. The next is NCI In EI and CI , positive ions are measured. But In NCI case ,negative ion is measured Reagent gas is　also　 required in NCI. In NCI case, the ionization can be occur at more than about 1Pa So the tightness of NCI ion source box lies midway between EI and CI. NCI is also soft ionization . NCI is occurred through electron capture reaction because ion is generated by electron attachment to sample molecules NCI is highly sensitive for molecules with high electron affinity, such as Halogenated compounds. In QP type mass spectrometer, ions are separated in quadrupole rods. Quadrupole rods are consists of four rods and the voltage is applied to each rod.（電圧のかけ方の絵） If the voltage V1 is applied to rod, ions with m1 can pass through but the ions with other mass go off course. So we can pass　 the ions with desired mass 　by applying appropriate voltage to rods If we varies the voltage continuously, the passing mass varies accordingly and we can get mass spectrum.