Why is the M+2 peak 4% and not 104% of M+ in sulfur mass spectrometry?

[lkh1986]

Homework Statement

An organic compound contains some C and H atoms and 1 S atom. Element sulfur, S has 2 isotopes, S-32 ans S-34. Their relative isotopic abundance is 100:4 (or 25:1). On the mass spectrometry graph, how would the peak of M+2 compared to that of M+'s peak?

Homework Equations

The Attempt at a Solution

This is a question in Wade Organic Chemistry book. The answer given in the book is that the peak at M+2 is 4% of that of M+'s peak. However, my lecturer points out that the book is wrong. He says that the peak of M+2 should be 104% of that of M+'s peak. Who is correct?

I think the book is correct. Since the ratio of compound with S-32 and S-34 is 25:1. So I don't see any reason why we need to add 100 to that 4.

 

[chemisttree]

You are right. Are you sure you heard the lecturer correctly?