MedChemExpress provides professional stable isotope-labeled compounds, such as 2H,13C, 15N, 18O, etc. They are widely used in proteomics and metabolomics of tracer research, NMR/MRI/MRS reagents, metabolic pathways, metabolic flux analysis (MFA), etc. And they can also be used as reference substances.
https://www.medchemexpress.com/isotope-compound/isotope-compound.html