*,*,*,*,*,*,*,*,Analytical Chemistry,分析化学,Analytical Chemistry分析化学,Chapter 15 Mass Spectroscopy,Chapter 15 Mass Spectroscop,15.1,Principles and Mass Spectrometer,15.2,Main Kinds of Ion Peaks,15.4,Mass Spectrum,and Structure,Determination,15.3,Cleavage Types of Organic Compounds,15.1 Principles and Mass Spec,Mass spectrometer,MS,is an instrument that is designed to ionize gaseous molecules,separate the ions produced on the basis of their,mass-to-charge ratio,and record the relative number of different ions produced.,Mass spectrum,is a plot of the data obtained from the mass spectrometer.It is a plot of the relative intensity of ions versus the mass/charge ratio(,m,/,z,).,Mass spectrometer MS is a,15,.,1,Principles and Mass Spectrometer,Sample,inlet,Ion,source,Mass,analyzer,Detector,1.,gas diffusion,2.,direct,3.,GC,1.,electron bombardment,2.,chemical ionization,3.,field ionization,4.,laser,1.,single focusing,2.,double focusing,3.,time-of-flight,4.,quadrupole,Mass spectrometer works at very low pressure:,ion source（10,-3,10,-5,Pa,）;,mass analyzer（10,-6,Pa,）.,15.1 Principles and Mass Spe,Why does Mass spectrometer works at vacuum?,Mass spectrometer works at very low pressure：,ion source（10,-3,10,-5,Pa,）;,mass analyzer（10,-6,Pa,）,(1),Filament of ion source may be damaged by oxygen,；,(2),Lead to discharge,；,(3),Cause other ion-molecular reaction;,Mass spectrometer is complex,。,Why does Mass spectrometer wo,Principle and structure,Principle and structure of ionization chamber,Principle Fig.,Principle and structurePrincip,The principle of mass analyzer,In magnetic field，when ion moves,:,centrifugal force=centripetal force,Kinetic energy of ion accelerated,:,(1/2),m,2,=,e V,(1),=(2,V,)/(,m,/,e,),1/2,(2),MS equation:,The principle of mass analyzer,MS equation,:,By changing the accelerated,voltage,ions of different,m,/,e,can be detected by the detector.,Sharpness of separation(,M,S,),=,M,/,M,MS equation:By changing the a,15,.,2,Main Kinds of Ion Peaks,1.,Molecular ion peak,(1)Molecule ionized by one electron forms the molecular ion and gives the molecular ion peak.,(2)The mass of the molecular ion is equal to the molecular mass of the compound.,(3)Intensity,of molecular ion peak depend on its stability.,(4)The molecular ion peak does not always existed in mass spectrogram.,15.2 Main Kinds of Ion Peaks,The stability of molecular ion :,Aromatic compoundalkenealicyclic compoundstraight chain paraffinketoneamine ester,etheracidbranched chain paraffin,alcohol,If there is a,molecular ion peak in mass spectrogram,its m/z is certainly the highest peak,The,energy of forming,molecular ion peak is low,about 10 eV,The,mass difference between,molecular ion peak and adjacent peak must be reasonable,e.g.15(-CH,3,),.,The stability of molecular ion,N,-rules:,If,a compound consists of C,H,O,the mass of the compound is definitely even.,If,a,compound consists of C,H,O,N:,a)If N number is odd,the molecular weight of the compound is definitely odd.,b)If N number is zero or even,the molecular weight of the compound is definitely even.,N-rules:If a compound consist,2.,Isotope peak（,M,+1,peak）,Due to isotope，,Isotope peak（M+1,peak）can be,observed in mass spectrum,；,sometimes,M,+2，,M,+3may be observed；,For a mass spectrum,if the relative intensities of,M,+2/,M,is 1:3,then the compound must contain Cl,For a mass spectrum,if the relative intensities of,M,+2/,M,is 1:1,then the compound must contain Br,2.Isotope peak（M+1 peak）Du,3.,Fragment ion peak,Ionization,energy of organic compounds,:,713,eV，,Ionization voltage in MS:,70,eV，,In the process of ionization,，,“,fragment ion”,was formed.,4.,Metastable ion peak,The base peak,The largest peak in a mass spectrum is termed the base peak.,3.Fragment ion peakIonizatio,15,.,3,Cleavage Types of Organic Compounds,ABCD +e,-,ABCD,+,+2e,-,molecular ion,碎,片,离,子,ABCD,+,BCD +A,+,B,+A,+,D +C,+,CD+AB,+,AB +CD,+,C +D,+,A,+B,+,Fragment ions,15.3 Cleavage Types of Organ,15,.,4,Structure Determination by Mass Spectrum（C,6,H,12,O,，,Ketone,）,Solution：,1100，,M.I peak,;,285，,lose CH,3,(15),;,357,base peak,stable structure,lose-CO(28),15.4 Structure Determination,分析化学英文ppt课件15质谱-Mass-Spectroscopy,