分析化学英文课件15质谱 Mass Spectroscopy

Aromatic compound＞alkene＞alicyclic compound ＞straight chain paraffin＞ketone＞amine ＞ester＞ ether＞acid＞branched chain paraffin＞alcohol ．
If there is a molecular ion peak in mass spectrogram, its m/z is certainly the highest peak．
M+2/M is 1:1, then the compound must contain Br
3. Fragment ion peak
Ionization energy of organic compounds: 7－13 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.
§15.3 Cleavage Types of Organic Compounds
ABCD + e - ABCD+ + 2e - molecular ion
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 .
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).
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.
= [(2V) / (m / e)]1/2 (2)
In magnetic field， when ion moves :
centrifugal force = centripetal force
m
R
2
H 0eV
(3)
R m
(4)
eH 0
MS equation :
MS equation :
m
H
2 0
Determination
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.
ABCD+
BCD• + A + CD• + AB +
AB • + CD +
B• + A +
碎
D• + C +
片
A•+ B+
离
子
C•+ D+
Fragment ions
§15.4 Structure Determination by Mass Spectrum （C6H12O，Ketone
） Solution：
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(-CH3).
(3) Intensity of molecular ion peak depend on its stability.
(4) The molecular ion peak does not always existed in mass spectrogram.
The stability of molecular ion :
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。
1．100，M.I peak ;
2．85，lose CH3(15); 3．57, base peak , stable structure
lose -CO(28)
Principle and structure
Principle Fig.
Principle and structure of ionization chamber
The principle of mass analyzer
Kinetic energy of ion accelerated:
(1 / 2)m 2 = e V (1)
b) If N number is zero or even, the molecular weight of the compound is definitely even.
2. Isotope peak（M+1 peak）
Due to isotope，Isotope peak（M+1 peak）can be observed in mass spectrum；sometimes M+2， M+3……may be observed；
R
2
e 2V
By changing the accelerated voltage, ions of different m / e can be detected by the detector.
Sharpness of separation (MS) = M / M
§15.2 Main Kinds of Ion Peaks
§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 ser
Analytical Chemistry 分析化学
Chapter 15 Mass Spectroscopy
§15.1 Principles and Mass Spectrometer §15.2 Main Kinds of Ion Peaks §15.3 Cleavage Types of Organic Compounds §15.4 Mass Spectrum and Structure
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 ）.
a) For a mass spectrum, if the relative intensities of
M+2/M is 1:3, then the compouectrum, if the relative intensities of