Carbon13

Carbon-13 is a stable isotope of carbon with atomic number 6 and a mass number of 13, consisting of 6 protons and 7 neutrons. It makes up about 1.07% of natural carbon. Like carbon-12, it is non-radioactive and chemically behaves similarly to its lighter counterpart, though its greater mass leads to small differences in vibrational frequencies and can influence reaction kinetics in some cases (the kinetic isotope effect is most pronounced for hydrogen isotopes).

A key property of carbon-13 is its nuclear spin, I = 1/2, which makes it observable by nuclear magnetic resonance (NMR) spectroscopy. Carbon-13 NMR is widely used for structural elucidation and conformational studies, often in combination with proton (1H) NMR. Because natural abundance is relatively low, researchers frequently use isotopically enriched samples to enhance signal.

Distribution and origin: carbon-13 occurs naturally in all carbon-containing materials and is formed in stars and through cosmic ray spallation processes. Its relatively low abundance means that isotope ratio analyses can reveal information about biogeochemical cycles and past environmental conditions.

Applications: carbon-13 is used in metabolic tracing with 13C-labeled substrates, allowing tracking of carbon flow through biochemical pathways. Isotope ratio mass spectrometry can measure the 13C/12C ratio in samples, yielding delta-13C values that are used in geology, archaeology, and paleoclimatology to study diet, climate, and carbon cycling. It is important to distinguish 13C from radiocarbon (14C), which is radioactive and used for dating.

Safety: carbon-13 is non-radioactive and considered safe for typical research use. See also isotopes of carbon, NMR spectroscopy, and isotope ratio mass spectrometry.