Mass Spectrometry

Question 1

What happens in mass spectrometry?

Answer 1

Vaporised organic sample is ionised (loses e-) and accelerated through mass spectrometer
M(g) —> M+(g) + e-
M+ (g) is detected (molecular ion)
Spectrometer measures mass/charge ratio (m/z)

Question 2

Why do mass spectra have many peaks?

Answer 2

Due to fragmentation. The excess energy from the ionisation process can transfer into the molecular ion, splitting it. This produces a smaller + ion and a radical.
The smaller (FRAGMENT ION) is detected

Question 3

How can you identify the original molecular ion in a mass spectra?

Answer 3

It is the peak furthest to the right with the largest m/z value because it is not fragmented.

Question 4

What is the M + 1 peak?

Answer 4

Carbon has C - 13 isotope of only 1% abundance so it is a very small peak to the right of M+ peak

Question 5

What molecular ion has an m/z value of 15?

Answer 5

CH3+

Question 6

What molecular ion has an m/z value of 17?

Answer 6

OH+ (from alcohols)

Question 7

What molecular ion has an m/z value of 29?

Answer 7

C2H5+

Question 8

What molecular ion has an m/z value of 43?

Answer 8

C3H7+

Question 9

What molecular ion has an m/z value of 57?

Answer 9

C4H9+