Isotopic Labelling

An isotope (an atom with a detectable change in neutron count) can be followed as it moves through a process, a metabolic pathway, or a cell using the technique known as isotopic labelling (or isotopic labelling). Specific atoms are "tagged" by substituting their isotopes in the reactant. The reaction is then let to happen on the reactant. The sequence that the isotopic atom followed in the reaction or the metabolic route of the cell is determined by measuring the location of the isotopes in the products. Radionuclides or stable nuclides can be employed for isotopic labelling. The labelling in the latter scenario is referred to as radiolabeling. The existence of labelling isotopes may be determined through isotopic labelling in a number of ways, including by their mass, vibrational mode, or radioactive decay. Infrared spectroscopy detects the difference in an isotope's vibrational modes, whereas mass spectrometry detects the difference in the isotope's mass. Atoms with various gyromagnetic ratios are found using nuclear magnetic resonance. An ionisation chamber or gel autoradiographs can be used to detect radioactive decay. The study of phenol (C₆H₅OH) in water using deuterium instead of common hydrogen (protium) is an illustration of the use of isotopic labeling. Phenol readily undergoes hydrogen-exchange reactions with water, as evidenced by the substitution of deuterium for the hydrogen in the hydroxyl group of the compound when it is added to deuterated water (water that contains D₂O in addition to the usual H₂O). The fact that only the hydroxyl group is impacted suggests that the exchange reactions do not involve the other 5 hydrogen atoms.