Because of its nuclear spin properties (spin +1/2, just like the hydrogen atom), this isotope responds to a resonant radiofrequency(RF) signal. The absorption and emission of the RF signal by the nuclei can be monitored and detected using NMR spectroscopy, a technique that gives information on the the identity and number of atoms adjacent to other atoms in said molecule = thereby giving clues to the structure of an organic molecule. C-12 has zero spin and does give a signal in NMR and since only 1% of the atoms in a molecule are C-13, it is unlikely that carbon-carbon coupling is seen and acquiring a carbon-13 NMR spectrum can take much time, often a couple of minutes or hours, because many scans have to be added together in order to have results distinguishable from background noise.

　　Detection by mass spectroscopy A mass spectrogram of an organic compound will usually contain a small peak of one mass unit greater than the apparent molecular ion peak (M). This is known as the M+1 peak and originates due to the presence of carbon-13 atoms. A molecule containing one carbon atom will be expected to have an M+1 peak of approximately 1.1% of the size of the M peak as 1.1% of the carbon atoms will be carbon-13 rather than carbon-12. Similarly a molecule containing two carbon atoms will be expected to have an M+1 peak of approximately 2.2% of the size of the M peak, as there is double the previous likelihood that a molecule will contain a carbon-13 atom.

　　In the above the mathematics and chemistry have been simplified, however it can be used effectively to give the number of carbon atoms for small to medium sized organic molecules. In the following formula the result should be rounded to the nearest integer:

　　C = number of C atoms X = amplitude of the M ion peak Y = amplitude of the M+1 ion peak

　　Carbon-13-enriched compounds are used in the research of metabolic processes by means of mass spectroscopy. Such compounds are safe because they are non-radioactive.en:Carbon-13 fi:Hiili-13