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1、質(zhì)譜儀 I 有機波譜分析 Organic Spectroscopic Analysis Mass Spectrometer I SCUEC(Li TC)2 MS Ionization：Desorption EI(1)&CI(2)are not suitable for nonvolatile or thermally fragile samples Desorption methods enable ions to be obtained from liquid or solid.Ion Source SCUEC(Li TC)3 MS Ionization：Desorption 1.Field

2、 Desorption(FD，場解吸場解吸)2.Fast Atom Bombardment(FAB，快原子轟擊快原子轟擊)3.Electrospray Ionization(ESI，電噴霧電離電噴霧電離)4.Laser Desorption(LD，激光解吸激光解吸)5.Matrix Assisted Laser Desorption/Ionization(MALDI，基質(zhì)輔助激基質(zhì)輔助激光解吸電離光解吸電離)Ion Source SCUEC(Li TC)4 場致電離源（場致電離源（FDFD）The field ionization source uses a strong electric f

3、ield to induce ionization of sample molecules.The strong electric field pulls out the electrons in the molecules near the tip.the resulting cations are desorbed due to coulombic repulsion.Ion Source Field Desorption(FD)10-12 kV is applied to emitter(a microneedle anode),creating at its tip an enormo

4、us E-field which ionizes the sample coated on the emitter,the resulting cations are desorbed due to coulombic repulsion.Usually M+dominates,with very little fragmentation.Ion Source 6 Soft Ionization for thermally labile compounds.Strong parent mass peak M+H+,M+Na+,M+K+Fragmentation pattern provides

5、 useful information.High chemical background defines detection limits Analyte must be soluble in the liquid matrix Moderate mass range:Typically 300 6000 Da.Fast Atom Bombardment(FAB)Ion Source Fast Atom Bombardment(FAB)Sample in a high b.p.liquid matrix (e.g.glycerol)is bombarded with a fast atom b

6、eam.Molecular-like ion and fragments are sputter-desorbed.Cluster ions from the matrix are also desorbed as background.1.Xe e-Xe+Xe 2.Xe+(accelerated to 6-10 keV)3.Xe+Xe+Xe (fast)Ion Source SCUEC(Li TC)8 FABFAB Ion Source 9 Two of the most common matrices used with FAB m-nitrobenzyl alcohol(NBA)glyc

7、erol Ion Source 10 Electro Spray Ionization John Fenn Nobel Prize in Chemistry 2002 “for their development of soft desorption ionisation methods for mass spectrometric analyses of biological macromolecules”Ion Source SCUEC(Li TC)12 High voltage applied to metal sheath(4 kV)Sample Inlet Nozzle(Lower

8、Voltage)Charged droplets+MH+M(H+)n M(H+)2 Pressure=1 atm Inner tube dia.=100 um Sample in solution N2 N2 gas Partial vacuum ESI Ion Source Ion Source ElectroSpray Ionization(ESI)For biomolecules(protein,polypeptide)with MW100,000 Operates at atmospheric pressure Ions desorbed from the droplet into t

9、he ambient gas.Features:Little fragmentation.Multiply charged ions smaller m/z values expand the detection with MS Ion Source SCUEC(Li TC)15 ESI Ion Source SCUEC(Li TC)16 Electrospray Ionization Pressure=1 atm Inner tube dia.=100 um Partial vacuum Ion Source ESI-MS Taken from http:/ are introduced i

10、n liquid solution.So ESI is compatible with HPLC for combined LC-MS A variety of mass analyzers can be used with ESI,including TOF,quadrupoles and ion traps.Ion Source hn Laser 1.Sample M mixed with matrix X 2.Laser ionizes matrix molecules 3.M ionized by proton transfer:XH+M MH+X MH+Matrix Assisted Laser Desorption Ionization (MALDI)+/-20 kV Grid(0 V)Sample www.msg.ucsf.edu/agard/maldi/IntrotoMS.ppt Ion Source MALDI-TOF-MS MALDI ionization,Time-of-flight Mass Spectrometer Ion Source