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

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

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

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+)

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

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

Isotopic Ratios – can tell us something about the elemental composition

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

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.

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

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

O2 Simulation software on http://www.sisweb.com/mstools/isotope.htm S

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

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