1. General Overview of the module and the methods
Amount of sample required
Self-explanatory
Information provided

2. s
Protein chemistry
See proteomics year 3
Small molecules
Traditional ‘organic’ chemistry

3. 12.1 Mass Spectrometry of Small Molecules:Magnetic-Sector Instruments
Measures molecular weight
Sample vaporized and subjected to bombardment by electrons that remove an electron
Creates a cation radical
Bonds in cation radicals begin to break (fragment)
Charge to mass ratio is measured

4. The Mass Spectrum
Plot mass of ions (m/z) (x-axis) versus the intensity of the signal (roughly corresponding to the number of ions) (y-axis)
Tallest peak is base peak (100%)
Other peaks listed as the % of that peak
Peak that corresponds to the unfragmented radical cation is parent peak or molecular ion (M+)

5. The mass spectrommeter can only detect charged particles
And what is measured is actually the mass of the molecule divided by the charge
Hence m/z ratio – but usually the charge is +1

6. Interpreting Mass-Spectral Fragmentation Patterns
The way molecular ions break down can produce characteristic fragments that help in identification
Serves as a “fingerprint” for comparison with known materials in analysis (used in forensics)
Positive charge goes to fragments that best can stabilize it
This cannot be detected
by the MS bec no charge

9. Isotopic Ratios – can tell us something about the elemental composition

10. Hypothetical mass spectra of atoms – characteristic pattern which reflects
natural terrestrial abundance of each isotope

11. Assign the peaks – means identifying the peaks in the
Mass spectrum – for simple molecules it is possible
To assign most peaks.
From this we can see that the Br2 radical
Cation does not fragment so easily – but
We are not expected to know why.

12. One could argue that the peak at 18
Is 18O – this is not impossible but most
Of the peak is due to the H2O

13. m/z 66 64 50 48 32 16
Assignment
34SO2+
32SO2+
34SO+
32SO+
O2 or S? (see next slide) O

14. O2
Simulation software on S

15. m/z 78 77 76 44 38 32 Assignment C34S32S+ C33S32S+ C32S2+ C32S+
Unusually a double + accounts for this

16. Homework Assign as many peaks as you can 1.Don’t write on spectrum
2. Do table in descending order of mass
m/z ratio assignment
HCHO
Don’t need to indicate isotopes except
for sulphur, bromine and chlorine.
Indicate for carbon only if it is helpful