Spectroscopy

Mass spectro tells you

the mass of the molecule

• via parent ion/molecular ion peak

Likely groups within a molecule

• via the mass of the fragments within the molecule OR the mass difference between the peaks

How mass spectro works

ionisation step removes an electron (it also can fragment the molecule and remove more than one e)

• becomes positively charged - mass spec can only detect positively charged substances (artificially generated ion)

Mass/charge signal (m/z) of COOH

45

CH3 m/z

15

OH m/z

17

What mass spectra looks like

base peak

fragment with the highest percentage abundance

Mass spectra: common mistakes

forgetting positive on fragment

Mass spectro isotopes effect

mass spec separates and detects m/z, different isotopes will impact on the position of peaks

When small tiny peak next to the molecular ion peak…

could be C-13 isotope - which is one unit apart from C-12 (longer peak)

35-Cl and 37-Cl

with relative ratio of 35-Cl: 37-Cl being 3:1 and two units apart

How mass spectra with Cl isotopes can look