Carbon-13 (13C) is a natural, stable isotope of carbon and one of the environmental isotopes. It makes up about 1.1% of all natural carbon on Earth. Pure carbon-13 costs about 700 USD per gram. Detection by NMR spectroscopy Because of its nuclear spin properties, this isotope responds to a resonant radio frequency (RF) signal. The absorption and emission of the RF signal by the nuclei can be monitored and detected using nuclear magnetic resonance spectroscopy, most commonly known as NMR spectr… (More on Carbon-13)