# Hill system with isotopologue

I'd like to use Hill notation (i.e. CH, then alphabetical), but I am not sure how to include isotopologues (i.e. carbon-13) in this notation.

For example, what would be the preferred form of ethylamine (with 13C)?

1. C13CH7N
2. CH713CN
3. 12C13CH7N
4. 12CH713CN
5. Other

I'm leaning toward using #2 but was trying to find the std practice, but I didn't see anything about isotopologues. Thanks.

$\ce{^{13}C\,^{12}CH_7N}%edit$