You most likely got here, because you followed the link in our Analytical Chemistry publication
Separation of ¹³C- and ¹⁵N‑Isotopologues of Amino Acids with a Primary Amine without Mass Resolution by Means of O‑Phthalaldehyde Derivatization and Collision Induced Dissociation
(https://doi.org/10.1021/acs.analchem.9b01788).
Unfortunately the link was misprinted. You really want to got to https://github.com/modsim/13C15N_abundance_correction