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# Mass spectrometry help pleaseee watch

1. Hi guys, can someone please tell me what's the difference between these terms?

M peak, M+ peak, M+1 peak, M+2 peak, M+3 peak

I found these from my Cgp book: here are the pages i found them from-

Attachment 729650729652
Attachment 729650729652729600
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2. (Original post by sienna2266)
Hi guys, can someone please tell me what's the difference between these terms?

M peak, M+ peak, M+1 peak, M+2 peak, M+3 peak

I found these from my Cgp book: here are the pages i found them from-

Attachment 729650729652
Attachment 729650729652729600
The molecular ion peak is assigned M+

Any versions of the molecule with less common isotopes which may be present can give rise to M+1, M+2, M+3 peaks

For example the M+ peak for CH3Cl occurs at m/z = 50, in which the chlorine atom is 35Cl

But there will be a smaller peak at m/z = 52 due to the M+2 version of the molecule in which the chlorine is 37Cl

and for C4H10 there is an M+ signal at m/z = 58

AND as the probability of 13C being about 1 in 100, then with 10 carbon atoms there is a 1 in 10 chance (i.e. intensity) of a signal at m/z = 59, this is an M+1 signal.
3. (Original post by charco)
The molecular ion peak is assigned M+

Any versions of the molecule with less common isotopes which may be present can give rise to M+1, M+2, M+3 peaks

For example the M+ peak for CH3Cl occurs at m/z = 50, in which the chlorine atom is 35Cl

But there will be a smaller peak at m/z = 52 due to the M+2 version of the molecule in which the chlorine is 37Cl

and for C4H10 there is an M+ signal at m/z = 58

AND as the probability of 13C being about 1 in 100, then with 10 carbon atoms there is a 1 in 10 chance (i.e. intensity) of a signal at m/z = 59, this is an M+1 signal.

Attachment 729826729830
Attached Images

4. (Original post by sienna2266)

Attachment 729826729830
They have called the molecular ion (labelled as such) "M"
It is probably to avoid confusion between M+ and M+1

The only particles detected by MS are ions, so it goes without saying that "M" is actually M+
5. (Original post by charco)
They have called the molecular ion (labelled as such) "M"
It is probably to avoid confusion between M+ and M+1

The only particles detected by MS are ions, so it goes without saying that "M" is actually M+
Thank you so much! Really appreciate your help!

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Updated: March 8, 2018
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