第八章质谱法.ppt
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1、第八章 质谱法,Mass Spectroscopy ( MS ),质谱仪的一般结构,真空系统,进样系统,离子检测器,数据系统,质量分析器,离子源,大气,样品,机械泵,分子涡轮泵,扩散泵, 离子泵,升华泵,气体:气相色谱仪(GC/MS) 液体:液相色谱仪(LC/MS) 固体:固体进样杆(DIP, DCI),电子倍增器,多通道板检测器 光电倍增管,阵列检测器,通常的离子化方法,电子轰击离子化 EI 化学电离离子化 CI 正化学电离离子化 PCI 负化学电离离子化 NCI 大气压力离子化 API 电喷雾离子化 ESI 大气压化学电离离子化 APCI,GC/MS,LC/MS,离子化方式,分子量,非极性
2、,极性,EI/CI,ESI,APCI,100,000,1000,离子化和碎片,离子化,硬,无碎片,有碎片,API,EI,CI,软,质量分析器,四极杆 80% 的台式质谱仪 (3000/年) HP, PE, TMQ, Shimadzu 离子阱 20%的台式质谱仪 (700/年) Varian, TMQ 飞行时间 (ToF) 目前用户较少 (50-60/年) Leco, Micromass, TMQ 扇形磁场 通常不是台式仪器,四极质量分析器,离子阱,原理与四极杆的非常相似,离子被存储在RF和DC场中,扫描场逐出精确m/z的离子。,飞行时间质量分析器,所有离子同时启动 小的离子移动速度快 测量已知
3、距离下的速度(飞行时间),扇形磁场质量分析器,离子通过变化的磁场和电场被传输,Electron Impact Ionization (EI),e-,e-,e-,e-,e-,Sample from GC,filament,+,+,+,+,Fragment ion,QP,Electron Impact Ionization (EI),Thermal electrons (ca. 70 eV) hit molecules and ionize them. Ample fragment ions = ample structural information Finger print,EI spectr
4、um Methylstearate M.W. 298,Positive Chemical Ionization (PCI),from gas cylinder,filament,QP,CH4,CH5+ C2H5+,Sample from GC,H+,-CH4,M+1,-C2H4,Positive Chemical Ionization (PCI),Reagent gas molecules are ionized first. Sample molecules are ionized mainly by 損roton transfer? Quasi molecular ions easily
5、produced useful for molecular weight verification.,+,PCI spectrum Methylstearate M.W. 298,Comparison of EI and PCI,EI mode,PCI mode,Negative Chemical Ionization (NCI),Negative ion formation by electron capture associative resonance capture dissociative resonance capture ion-pair production Negative
6、ion formation by ion-molecule reactions proton transfer charge exchange nucleophilic addition nucleophilic displacement,Negative ion formation by electron capture (associative resonance capture),MX + e- (0 eV) MX-.,X: positive electron affinity part,CH4,MX,CH4,+,CH3,+,H,CH4,CH4,CH4,e-,MX,-,质谱图的样子?,E
7、I和CI的质谱图,m/z,0,100,%,510,511,512,m/z,0,100,%,241,213,510,242,EI,NCI,扫描50到300amu流入质谱仪的化合物,质谱图.,断裂机理,1.断裂,2. 断裂,3. i 断裂,4. 逆 Diels-Alder 反应,5. Mclafferty 重排,Configuration of GCMS,Mass Spectrometer,Gas Chromatograph,Interface,Ion source box,Ion Source Design - Increased ionization efficacy -,Interface
8、The sample separated by GC will be introduced through this interface.,Filament Ion generated by filament will give the electron impact to the sample to produce the sample ionization.,Ion source box,Ion Lens - High ion introduction to mass analyzer -,This ion lens is functioning for effective introdu
9、ction to mass analyzer. Optimization for adjustment of this ion lens will be done by PC automatically.,Quadrupole Rod - Minimize losses in transit to the Quadrupole -,Main Rod Specific ion only can be passed by the electronic field into Quadrupole Rod which is controlled by PC.,Pre Rod,From ion sour
10、ce,To detector,rotary pump turbo molecular pump (151 L/sec),turbo molecular pump(151 L/sec),rotary pump,Good vacuum system - Minimize losses in transit to the Quadrupole -,Turbo Molecular Pump,Air cooled and oil free Turbomolecular Pump (TMP) with lubricant impregnated ceramic bearings is maintenanc
11、e free for up to 25,000 hours. Provides high quality vacuum in less than 5 mins.,Ion detection,Negative ion detection,Positive ion detection,GCMS-QP5050A NCI sensitivity,200fg Hexachlorbenzene,NCI spectrum,Mass chromatogram of m/z284,OFN (octafluoronaphthalene) NCI scan mode,Outstanding High Sensiti
12、vity,scan range m/z 60-310, 0.5sec interval,200fg S/N 30,GCMS-QP5050A NCI pesticides date 3,10pg Cyanophos NCI mass spectrum,phosphorus pesticides 10pg,Comparison between EI and NCI extract from cabbage (pesticides added),EI scanning mode,NCI scanning mode,Comparison between EI and NCI extract from
13、cabbage (pesticides added),Principle of Programed temperature vaporize (PTV),PTV,100C,split,MS,50-250C,Solvent will be vaporized and exhausted. Sample will be concentrated.,Optimization of PTV conditions,Selection of packing materials Tenax GC 20% OV-1 20% OV-17 20% Dexil 300 Shincarbon A Carbopack
14、C Trap temperature Desorption temperature Temperature program,Very-Large-Volume Injection using PTV Effect of Temperature on Trap efficiency,Very-Large-Volume Injection using PTV Temperature and Split ratio Program,Very-Large-Volume Injection using PTV 2ppb each Pesticides in n-hexane 1000 uL Inject
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