JS
Registered: 10/06/09
Posts: 18
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Reply with quote | #1 |
What would happen if a molecule had two bromine atoms? Would the relative intensity of M+2 be double that of M? Would it therefore be impossible for the molecular ion (M) to be the base peak?
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DrH
Moderator
Registered: 09/22/08
Posts: 431
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Reply with quote | #2 |
M+2 intensities are additive. In other words, the mass spectrum for a molecule with two bromine atoms, when M has a relative abundance of 100%, M+2 is very nearly 200%. If one bromine and one chlorine is present, M+2 is ~135%. |
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jamar
Registered: 10/12/09
Posts: 17
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Reply with quote | #3 |
I understand the additive property Dr. Hardinger. But in that situation, if M+2 were to be 200% relative to M, would we reassign M+2 as the 100% base peak and make M proportionally smaller at 50%?
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dhlee624
Registered: 10/08/09
Posts: 19
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Reply with quote | #4 |
Quote: Originally Posted by jamar
I understand the additive property Dr. Hardinger. But in that situation, if M+2 were to be 200% relative to M, would we reassign M+2 as the 100% base peak and make M proportionally smaller at 50%?
I believe M is always set to 100% as the relative ion abundance and M+1 and M+2 are set relative to that.
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DrH
Moderator
Registered: 09/22/08
Posts: 431
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Reply with quote | #5 |
We set M = 100% (regardless of the relative abundance of other peaks) to use M, M+1, and M+2 to determine molecular formula. There is no general rule that states "M is always always 100%". |
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