# Mass spectrometry

The mass spectrum of butanone shows its main peak at m/z 72. It also has. Small signal at m/z 73.

C) Give two reasons for the peak at m/z 73

D) there would also be tiny peaks at m/z 74,75 etc. Explain why some ions with these m/z values may be formed but why their signals may be too small to be seen.
Original post by TryingtogetA*
The mass spectrum of butanone shows its main peak at m/z 72. It also has. Small signal at m/z 73.

C) Give two reasons for the peak at m/z 73

D) there would also be tiny peaks at m/z 74,75 etc. Explain why some ions with these m/z values may be formed but why their signals may be too small to be seen.

Its all about the isotopes - butanone contains, H, C and O
The m/z is for the ‘normal’ isotopes as you would expect them to be from the periodic table
Original post by BankaiGintoki
Its all about the isotopes - butanone contains, H, C and O
The m/z is for the ‘normal’ isotopes as you would expect them to be from the periodic table

How would I go about it tho I literally have no idea on what to do
Original post by TryingtogetA*
How would I go about it tho I literally have no idea on what to do

For C) I will give a reason
Butanone sample contained a single hydrogen with 1 proton and neutron - so m/z will be 73
As that hydrogen has a mass number 2, which is 1 greater than a ‘normal’ hydrogen isotope
Original post by BankaiGintoki
For C) I will give a reason
Butanone sample contained a single hydrogen with 1 proton and neutron - so m/z will be 73
As that hydrogen has a mass number 2, which is 1 greater than a ‘normal’ hydrogen isotope

Thank you but what about D my teacher didn't really go into detail on this part of the unit
Original post by TryingtogetA*
Thank you but what about D my teacher didn't really go into detail on this part of the unit

https://www.chemguide.co.uk/analysis/masspec/fragment.html
Ions are formed from the fragmentation process
Unstable ions break further
As peaks 73,74,75… are further from the m/z peak, its the same reasoning - isotopes
Butanone with multiple isotopes with more neutrons
Those isotopes are rarer, and need to be in the same butanone molecule
(edited 8 months ago)