mass spectrometery

in this presentation we learn about the mass spectrometery principal and its mass to charge ratio.
components of mass spectrometers .
sample inoculation and its processing. i feel these are very good slides.

1. Mass spectrometry Rabia shehzadi 1730814-012

2. CONTENTS INTRODUCTION HISTORY PRINCIPLE MASS SPECTROMETER COMPONENTS OF MASS SPECTROMETER SAMPLE INTRODUCTION METHODS

3. Introduction Mass spectrometry is a powerful analytical technique used to quantify known materials, to identify unknown compounds within a sample and to elucidate the structure and chemical properties of different molecules . It depends upon chemical reactions in the gas phase in which sample molecules are consumed during the formation of ionic and neutral species. This will be happened by converting the material to charged molecules to measure their mass to charge ratio.

4. HISTORY Mass spectroscopy was first performed at the Cambridge university , in 1912 by J.J Thomson (1856-1940) when he obtained the mass spectra of O2, N2, CO. Mass spectroscopy took off in 1930s and advance technology resulted in the development of double focusing Mass spectrometers capable of accurate determination. The modern techniques of mass spectrometry were devised by Arthur Jeffrey Dempster and F.W. Aston in 1918 and 1919 respectively. In 2002, the Nobel Prize in Chemistry was awarded to John Bennett Fenn for the development of electrospray ionization (ESI )

5. MASS SPECTROMETER It is an instrument in which the substances in gaseous or vapor state is bombarded with a beam of electrons, to form positively charged ions (cations) which are further sorted according to their mass to charge ratio to record their masses and relative abundances.

6. PRINCIPLE In mass spectrometry, organic molecules are bombarded with a beam of energetic electrons (70 eV) in gaseous state under pressure between 10-7 to 10-5 mm of Hg, using tungsten or rhenium filament. Molecules are broken up into cations and many other fragments. These cations (molecular or parent ion) are formed due to loss of an electron usually from n or π orbital from a molecule , which can further break up into smaller ions (fragment ions or daughter ions). All these ions are accelerated by an electric field, sorted out according to their mass to charge ratio by deflection in variable magnetic field and recorded. The output is known as mass spectrum. Each line upon the mass spectrum indicates the presence of atoms or molecules of a particular mass.

7. principle

8. COMPONENTS OF A MASS SPECTROMETER The essential components of a mass spectrometer consist of: A sample inlet An ionization source A mass analyzer An ion detector Vacuum system

9. MASS ANALYZER QUADRUPOLE, MAGNETIC SECTORS, TIME OF FLIGHT, QIT, FTICR INLET SYSTEM FOR SOLIDS, FOR LIQUIDS, FOR GASES DETECTOR ELECTRON MULTIPLIER, FARADAY CUP, PHOTOMULTIPLIER CONVERSION DYNODE, ARRAY IONIZATION MECHANISMS: PROTONATION, DEPROTONATION, CATIONIZATION, ELECTRON EJECTION, ELECTRON CAPTURE IONIZATION SOURCE ESI, MALDI, FAB, FD, PD, APCI, APPI, EI, CI, FI. MASS SPECTROMETER

10. Mass spectromter

11. SAMPLE INTRODUCTION METHODS 1 . Direct Vapor Inlet The simplest sample introduction method. The gas phase analyte is introduced directly into the source region of the mass spectrometer through a needle valve. Pump out lines are usually included to remove air from the sample. This inlet works well for gases, liquids, or solids with a high vapor pressure. It only works for some samples.

12. Gas Chromatography Most common technique for introducing samples into a mass spectrometer. Complex mixtures are routinely separated by gas chromatography and mass spectrometry is used to identify and quantitate the individual components. The most significant characteristics of the inlets are the amount of GC carrier gas that enters the mass spectrometer and the amount of analyte that enters the mass spectrometer. Ideally all the analyte and none of the GC carrier gas would enter the source region . The most common GC/MS interface now uses a capillary GC column

13. Liquid Chromatography LC inlets are used to introduce thermally labile compounds not easily separated by gas chromatography. These inlets are used for temperature sensitive compounds. The sample is ionized directly from the condensed phase.

14. Direct Insertion Probe The Direct Insertion Probe (DIP) is widely used to introduce low vapor pressure liquids and solids into the mass spectrometer. This is important for analyzing temperature sensitive compounds. Although the direct insertion probe is more cumbersome than the direct vapor inlet, it is useful for a wider range of samples.

15. Direct Ionization of Sample Some compounds either decompose when heated or have no significant vapor pressure and can be introduced by direct ionization from the condensed phase.

16. IONIZATION METHODS Protonation Protonation is a method of ionization by which a proton is added to a molecule, producing a net charge of 1+ for every proton added. E.g .: More basic residues of the molecule, such as amines; Peptides. Can be achieved through MALDI, ESI and APCI.

17. Electron Capture With the electron capture ionization method, a net charge of 1- is achieved with the absorption or capture of and electron. E.g.: Molecules with high electron affinity, such as halogenated compound

18. Electron Ejection Ionization is achieved through the ejection of an electron to produce a 1+ net charge , often forming radical cations. It generates significantly fragmented ions . E.g .: Non-polar compounds with low molecular weights. Most commonly achieved with electron ionization (EI) sources.

19. Cationization It produces a charged complex by non-covalently adding a positively charged cation adduct (e.g. alkali, ammonium) to a neutral molecule. E.g.: Carbohydrates are best examples, with Na+ as a common cation adduct. Mainly achieved by MALDI, ESI and APCI.

20. Electron Capture With the electron capture ionization method, a net charge of 1- is achieved with the absorption or capture of and electron. E.g.: Molecules with high electron affinity, such as halogenated compounds

21. Transfer of a Charged Molecule to the Gas Phase The transfer of compounds already charged in solution is achieved through desorption or ejection of the charged species from the condensed phase into the gaseous phase. Commonly achieved through MALDI or ESI.

22. GENERAL MODES OF FRAGMENTATION SIMPLE CLEAVAGE REARRANGEMENT REACTIONS ACCOMPANIED BY TRANSFER OF ATOMS SKELETAL REARRANGEMENT

23. cleavage In this type of cleavage both the electrons of the α bond are taken over by one of the atoms; the fragments are even electroncation and a radical with the positive charge residing on the alkyl group. It may be noted that the cleavage of C ̶X (X= O,N,S, Cl ) bond is more difficult than that of a C ̶C bond. It can be shown by fragmentation of alkyl halide.

24. REARRANGEMENT REACTIONS ACCOMPANIED BY TRANSFER OF ATOMS It involves the migration of γ-hydrogen atom followed by the cleavage of a β- bond. The rearrangement leads to the elimination of neutral molecules from aldehydes, ketones, amines, unsaturated compounds etc . The rearrangement proceeds through a sterically hindered six membered transition state. The structural requirements for this reaction are a side chain of at least three carbon atoms bearing a γ-hydrogen and a double bond which could be a carbonyl group or an olefinic double bond or an aromatic system

25. Conti….

26. SKELETAL REARRANGEMENT Induced by radical or charge sites or both may found to have some influence on rearrangement processes. Unsaturated esters and carbonates undergo rearrangements with the loss of carbon dioxide