Mass spectrometry

How does mass spectrometry identify organic molecules?

A beam of e- fired at a sample causing loss of e'- and forms molecular ions that are passed through MS.

Molecular ion

The loss of e- and ion formed.

E.g Pentane C5H12

pentane molecular ion:

C5H12+

m/z ratio

tells us mass it molecular ion

M+ peak

Peak tell us the relative formula mass of the organic molecule.

Peak at 72 (Pentane rfm)

M+1 peak

due to presence of C-13 isotope which makes up 1% of carbon atoms

Why are there multiple peaks

due to fragmentation of organic molecules in Mass spectrometer. Causes formation of ions/radicals.

E.g m/z ratio of CH3 = 15 (peak at 15)

uses of mass spectrometer

• breathalysers

• monitoring of air pollution

• MOT emission testing