MS Solutions - Isotope Peak Intensity Calculations

[RFS]

After reading the latest MS solutions article, I have one question.

Why is the number of carbons squared in the calculation of relative intensities for X+2 peaks. I do not see this used in the calulations for other elements that contribute to X+2 intensity. Does it have something to do with carbon having an X+2 contribution, but not actually having a significant X + 2 isotope?

Thanks

[Don_Hilton]

The abundance of the X+n peak is the probability of n atoms in the molecule being the A+1 isotope. So, you are looking at the probabilty of the occurance of 13C to happen twice. If the probability of an event occuring is p then the probability of the event occuring twice is p*p.

[lmh]

Here's a link:
http://www.jic.ac.uk/Services/Metabolom ... socalc.htm