1、 Organic Spectroscopic Analysis Principles of Mass Spectrometry Introduction to Mass Spectrometry MS,Sample Inlet Ion Source Mass Analyzer Detector Recorder ionizes sample molecules;separates them according to their mass(m)-to-charge(z)ratios(m/z);records a mass spectrum.How does a mass spectrometer
2、 work?1.The sample has to be introduced into the ionisation source of the instrument.Once inside the ionisation source,the sample molecules are ionised.2.These ions are extracted into the analyser region of the mass spectrometer where they are separated according to their mass(m)-to-charge(z)ratios(
3、m/z).3.The separated ions are detected and this signal sent to a data system where the m/z ratios are stored together with their relative abundance for presentation in the format of a m/z spectrum.How does a mass spectrometer work M e M+Ionization Energy Mass Spectrum RI relative intensity%The RI of
4、 the base peak is 100%.Most intense peaks will arise from stable ions and from cleavages that occur most readily 8 2.Ion source(离子源)Electron Impact（EI，电 子 轰 击 离 子 源）Chemical Ionization（CI,化学电离源）Field Desorption(FD，场解吸)Fast Atom Bombardment(FAB，快原子轰击)Electrospray Ionization(ESI，电喷雾电离)Laser Desorption
5、(LD，激光解吸)Matrix Assisted Laser Desorption/Ionization(MALDI，基质辅助激光解吸电离)Electron Impact(EI)Very energetic Ions are produced Fragmentation M.+is often weak or absent(e.g.ROH often loose H2O)Intensity of M.+depends on stability of the Ion:Most Stable Aromatic Conjugated Alkene Cyclic compound Sulfide Sh
6、ort Linear Alkane Mercaptan Least Stable M.+is often absent in:Ketone Amine Ester Ether Acid Amide Aldehyde Alcohols,Nitriles,Nitrates,Nitro M+e(70eV)-M+.+2e Ion Source Electron Impact Ionization Source Ion Source Electron Impact(EI)Ion Source Chemical Ionization(CI)In CI,ion molecule reactions occu
7、r between ionized reagent gas molecules G and volatile analyte neutral molecules(M)to produce analyte ions.Pseudo-molecular ion MH+(positive ion mode)or M-H-(negative ion mode)are often observed.Unlike molecular ions obtained in EI method,MH+and M-H-detection occurs in high yield and less fragment i
8、ons are observed.Positive ion mode:GH+M-MH+G Negative ion mode:G-H-+M-M-H-+G The main reagent gases used in CI are:Ammonia,Methane,and Isobutane.Choice of reagent gas affect the extend of fragmentation of the quasi-molecular ion.Ion Source Ion Source Proton transfer is one of the simple processes ob
9、served in positive CI:RH+M-MH+R One of the decisive parameter in this reaction is the proton affinity.For the reaction to occur,the proton affinity of the molecule M must be higher that the one of the gas molecule.The main reagent gases used in CI are:Ammonia,Methane,and Isobutane.Choice of reagent gas affect the extend of fragmentation of the quasi-molecular ion.Chemical Ionization(CI)Ion Source
