I just began studying mass spectroscopy and I just seem to understand why certain peaks are not indicted in mass spectrum graph. Like lets say you have methyl or ethyl bromide. Usually, there is two equal peaks at right most side indicate 1:1 ratio of Br -79 and 89 isotopes. But this is only when you assume all carbon atom is C-12?

• Why does not graph show peak with combination of C-13 and bromine isotopes?

None of the examples online indicate this.

I just began studying mass spectroscopy and I don't understand why certain peaks are not represented in the mass spectrum graph. Like let's say you have methyl or ethyl bromide. Usually, there are two equal molecular ion peaks at the right-most side, which indicate a $1:1$ ratio of $\ce{^{79}Br}$ and $\ce{^{81}Br}$ isotopes. 

But this is only when you assume all carbon atom are $\ce{^{12}C}$. Why doesn't the graph show peaks with combination of $\ce{^{13}C}$ and bromine isotopes?

None of the examples online indicate this.

I just began studying mass spectroscopy and I just seem to understand why certain peaks are not indicted in mass spectrum graph. Like lets say u have methyl or ethyl bromide. Usually, there is two equal peaks at right most side indicate 1:1 ratio of Br -79 and 89 isotopes. But this is only when u assume all carbon atom is C-12? Why does not graph show peak with combination of C-13 and bromine isotopes? None of the examples online indicate this. Pls help!!!

I just began studying mass spectroscopy and I just seem to understand why certain peaks are not indicted in mass spectrum graph. Like lets say you have methyl or ethyl bromide. Usually, there is two equal peaks at right most side indicate 1:1 ratio of Br -79 and 89 isotopes. But this is only when you assume all carbon atom is C-12?

• Why does not graph show peak with combination of C-13 and bromine isotopes?

None of the examples online indicate this.