Isotope labeling is a technique used to track isotopes (atoms with detectable neutron count changes) through reactions, metabolic pathways, or cellular channels. The reactant is "labeled" by replacing specific atoms with its isotopes. The reactant is then allowed to undergo the reaction. The position of isotopes in the product is measured to determine the sequence of isotope atoms in the reaction or the metabolic pathway of the cell. In isotope labeling, there are many methods to detect the existence of labeled isotopes. The difference of isotope mass was detected by mass spectrometry, while the difference of isotope vibration mode was detected by infrared spectrum. Nuclear magnetic resonance (NMR) is used to detect atoms with different gyromagnetic ratios. isotopically labeled chemicals https://bioconjugation.bocsci.com/services/stable-isotope-labeling.html