Mass spectrometry

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LOGO Introduction of Mass Spectrometry PRESENTED BY SALMAN ZAFAR 163 INORGANIC CHEMISTRY S E COLLEGE BWP PAKISTAN [email protected]

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briefly discruption about mass spectrometry

Transcript of Mass spectrometry

  • 1. LOGO PRESENTED BY SALMAN ZAFAR 163 INORGANIC CHEMISTRY S E COLLEGE BWP PAKISTAN [email protected]

2. CONTENT DEFINATION INTRODUCTION HISTORY MASS SPECTROMETER PRINCIPLE STRUCTURE ANALYSIS FRAGMENTATION EXSAMPLES 3. DEFINATION Mass spectrometry is the most accurate technique to determine the molecular mass and molecular composition of organic and inorganic compounds. It provides both qualitative and quantitative information about the molecular composition of organic and in organic compounds. It is also called positive ion spectra or line spectra. 4. Powerful analytical technique Smallest scale Destructive technique Useful for identification of species According to the IUPAC (International Union of Pure and Applied Chemistry), it is the branch of science dealing with all aspects of mass spectrometers and results obtained with these instruments. 5. INTRODUCTION Why we say mass spectrometry not mas spectroscopy? In mass spectrometry there is no absorption of electromagnetic radiations. It is just a measurement of molecular weights of different molecules in a compound according to their m/z ratio. 6. 1897 1919 1934 1966 J.J. Thomson. Discovered electrons by cathode rays experiment. Nobel prize in 1906. Francis Aston recognized 1st mass spectrometer and measure z/m of ionic compounds. First double focusing magnetic analyzer was invented by Johnson and Neil. Munson and Field described chemical ionization. Brief History of Mass Spectrometry 7. 1968 1975 1985 1989 Electrospray Ionization was invented by Dole, Mack and friends. Atmospheric Pressure Chemical Ionization (APCI) was developed by Carroll and others. F. Hillenkamp, M.Karas and co-workers describe and coin the term matrix assisted laser desorption ionization (MALDI). w. Paul discovered the ion trap technique. 8. Joseph John Thomson 1906 Nobel Prize for Physics (theoretical and experimental investigations on the conduction of electricity by gases) Francis William Aston 1922 Nobel Prize for Chemistry (mass spectrograph, of isotopes, in a large number of non- radioactive elements) Wolfgang Paul 1989 Nobel Prize for Physics (for the development of the ion trap technique) John Bennet Fenn 2002 Nobel Prize for Chemistry (for the development of Soft Desorption ionization Method) Koichi Tanaka 2002 Nobel Prize for Chemistry (mass spectrometric analyses of biological macromolecules) Nobel prize pioneers 9. Mass spectrometer 10. Mass spectrometer is similar to a prism. In the prism, light is separated into its component wavelengths which are then detected with an optical receptor, such as visualization. Similarly, in a mass spectrometer the generated ions are separated in the mass analyzer, digitized and detected by an ion detector. 11. Basic Components of Mass Spectrometer Four basic components Sample inlet Ionization source Mass analyzer Ion detector 12. Understanding Mass Spectrometry In a mass spectrometer, the same thing is happening, except it's atoms and molecules that are being deflected, and it's electric or magnetic fields causing the deflection. It's also happening in a cabinet that can be as small as a microwave or as large as a chest freezer. 13. PRINCIPLE First of all sample is bombarded with high electron beam produce the positive ions. They travel in a straight path. When a magnetic field or electric field is applied they travel in curved path. The fragments of different masses are separated based on the radius of curvature. m/z r These are then detected on detector. 14. VIDEO 15. VIDEO 16. STRUCTURE ANALYSIS Structural analysis and Fragmentation Patterns Mass spectrum Graph of ion intensity (relative abundance) along x-axis versus mass-to-charge ratio (m/z) (units daltons, Da) along Y-axis Molecular ion (Parent ion) Fragmentation peaks Base peak Isotopic peaks 17. MOLECULAR ION PEAK the peak corresponding to the mol. wt.of the compound The peak of an ion formed from the original molecule by electron ionization, by the loss of an electron, or by addition or removal of an anion or cation and also known as parent peak, radical peak. Molecular ion (Parent ion) 18. ISOTOPIC PEAKS 19. NATURAL ABUNDANCE 20. NATURAL ABUNDANCE M M+1 M+2 Silicon :28Si: 100 29Si: 5. 2 30Si : 3.35 21. ISOTOPIC PEAKS 79Br 22. BASE PEAK Base peak The most intense (tallest) peak in a mass spectrum, due to the most abundant ion. Not to be confused with molecular ion: base peaks are not always molecular ion and molecular ion are not always base peaks. 23. FRAGMENTATION The process of breaking molecules/ions into fragments is known as fragmentation. This can be seen in the form of peaks in mas spectra. Methanol can be divided into four fragments. e.g. CH3OH CH3OH* + e CH3OH CH3* + OH CH30H CH2OH* + H CH30H CHO* + H2 24. FRAGMENTATION PEAKS 120 100 80 60 40 20 0 . 5 10 15 20 25 30 35 120 100 80 60 40 20 0 CHO CH3OH CH3 CH2OH m/e 25. RULES OF FRAGMENTATION Intensity of M+ is larger for linear chain than for branched compounds. Intensity of M+ decrease with increasing molecular weight. (exception of fatty acids) Cleavage is favored at branching. Aromatic rings, Double bond, Cyclic structure stabilize M+ 26. RULES OF FRAGMENTATION 1.Hydrocarbons Hydrocarbons give clusters of peaks. Molecular ion peaks of very low abundance are observed for linear hydrocarbons. For branched hydrocarbons give a low intensity at M+. Intensity of (CnH2n+1) peaks decreases with increasing mass. 27. STRUCTURE ANALYSIS DBR Calculations Nitrogen Rule 28. STRUCTURE ANALYSIS DBR Calculations Double bond or ring calculations tell us about how many rings or double bonds are present in a compound. DBR= C-H/2+N/2+1 C= number of carbon atoms H= number of hydrogen atoms N= number of nitrogen atoms 29. STRUCTURE ANALYSIS Nitrogen Rule If a compound contains an even number of nitrogen atoms (or no nitrogen atoms), its molecular ion will appear at an even mass number. If, however, a compound contains an odd number of nitrogen atoms, then its molecular ion will appear at an odd mass value. This rule is very useful for determining the nitrogen content of an unknown compound. 30. Mass spectra (examples) Alkanes Strong M+ (but intensity decreases with an increase of branches. Carbon-carbon bond cleavage loss of CH units in series: M-14, M-28, M-42 etc 31. Alkanes 32. Alkenes Strong M+ Fragmentation ion has formula CnH2n+ and CnH2n-1 -Cleavage A series of peaks: M-15, M-29, M-43, M-57 etc 33. Alkynes Strong M+ Strong base peak at M-1 peak due to the loss of terminal hydrogen Alpha cleavage 34. Aromatic Hydrocarbons Strong M+ Loss of hydrogen gives base peak McLafferty rearrangement Formation of benzyl cation or tropylium ion 35. EXAMPLE Alcohols M+ weak or absent Loss of alkyl group via a-cleavage Dehydration (loss of water) gives peak at M-18 36. LOGO [email protected] S E COLLEG BWP PAKISTAN