INTERPRETATION OF MASS SPECTROSCOPY

interpretation of mass spectroscopy.fragmentation process

1. BASIC PRINCIPLES IN INTERPRETATION OF MASS SPECTRA KOMMINENI.VIDYA (09ED1R0006) Under the guidance of K.PRAVEEN KUMAR M.Pharm ( Ph.D )

2. Mass spectrometry Mass spectrometry is the most accurate method for determining the molecular mass of the compound and its elemental composition. It is also called as positive ion spectra or line spectra.

3. Introduction Mass spectrometry (Mass Spec or MS) uses high energy electrons to break a molecule into fragmentation. A beam of high-energy electrons breaks the molecule apart. The masses of the fragments and their relative abundance reveal information about the structure of the molecule. Separation and analysis of the fragments provides information about: Molecular weight Structure

4. General approach for acquiring information about a sample degree of unsaturation Structures and functional groups Connectivity of structures Reference spectra and comparison to possible structures where unique identification is not possible

5. GENERAL RULES FOR INTERPRETATION OF MASS SPECTRA . In order to interpret the mass spectrum , one should attain an understanding of the ionisation process. . To observe fragmentation pattern. 1.The exact molecular weight: The molecular weight of a pure compound from the identification of the parent peak. The molecular weight one can determine molecular formula. 2.The isotope effects : Heavy isotopes will exhibit peaks in a mass spectrum at m/e one or more units higher than normal. i.e.,there will be small peaks at M+1 and M+2.

6. The nitrogen rule In organic compounds , is a relationship between the valance and the mass of the most common isotope for most elements. Even elements have an even valance. Odd elements have an odd valance. This leads to the ‘nitrogen rule.’ It assumes that we are limiting our elements to C, H, halogens, O and N.

7. The nitrogen rule A compound containing only C, H, O or X will have an even molecular weight. A compound with an odd number of nitrogens will have an odd molecular weight. A compound with an even number of nitrogens will have an even molecular weight.

8. Logical losses

9. General steps in mass spectral interpretation

10. What is a mass spectrum

11. m/z ratio: M olecular weight divided by the C harge on this protein All proteins are sorted based on a mass to charge ratio (m/z)

12. RELATIVE ABUNDANCE: It is a method of reporting the amount of each mass to charge measurement after assigning the most abundant ion 100%. Abundance: . The amount of an isotope of an element that exists in nature , usually expressed as a percentage of the total amount of all isotopes of the element.

13. A simple mass spectrum

14. A simple mass spectrum

15. A simple mass spectrum

16. A simple mass spectrum

17. A simple mass spectrum

18. Fragmentation pattern

19. What is base peak? 100% abundance is called as base peak . M - is parent ion peak . It is all so called as molecular ion peak . Molecular peak of M produced when an electron is ejected from the molecule M + e - M + +2e -

20. Background of fragmentation The impact of a stream of high energy electrons causes the molecule to lose an electron forming a radical cation . A species with a positive charge and one unpaired electron. Molecular ion M/z=16

21. Background The impact of the stream of high energy electrons can also break the molecule or the radical cation into fragments. m/z = 15

22. Background Molecular ion (parent ion): The radical cation corresponding to the mass of the original molecule The molecular ion is usually the highest mass in the spectrum Some exceptions specific isotopes Some molecular ion peaks are absent.

23. Background Mass spectrum of ethanol(MW = 46)(C 2 H 5 OH) M +

24. Background M + base peak The mass spectrum of ethanol

25. Fragmentation Patterns The impact of the stream of high energy electrons often breaks the molecule into fragments, commonly a cation and a radical. Bonds break to give the most stable cation. Stability of the radical is less important.

26. Fragmentation Patterns Alkanes Fragmentation often splits off simple alkyl groups: Loss of methyl M + - 15 Loss of ethyl M + - 29 Loss of propyl M + - 43 Loss of butyl M + - 57 Branched alkanes tend to fragment forming the most stable carbocations.

27. Fragmentation Patterns Mass spectrum of 2-methylpentane(M.w-86)

28. Example:

29. ASPIRIN (or) SALICYLICACID(m.wt-180)

30. Mass spectra of toulene :(m/z=91)

31. Conclusion We’ve totally left out any of the mechanisms of ion fragmentation. On the other hand, the assumption was that you were working with a GC/MS system. The chromatographic information will also help solve many problems.

32. THANKYOU