Carbon-13
From Freepedia
Carbon-13 is a stable isotope of carbon. It makes up about 1.109% of all naturally-occurring carbon on Earth.
Detection by NMR spectroscopy
Because of its spin properties (it can have positive and negative spin, just like the hydrogen atom), the presence of this isotope can be detected using NMR spectroscopy, giving information on the structure of an organic molecule, namely, the number of carbon atoms in said molecule. Because of its trace presence, running a carbon-13 NMR scan can take much time, often a couple of minutes or hours, because many scans have to be run and then combined using a Gaussian interpolation 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:
<math>C = \frac{100Y}{1.1X}</math>
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.
| Carbon-12 | Isotopes of Carbon | Carbon-14 |
| Produced from: Nitrogen-13 Boron-13 | Decay chain | Decays to: Stable |
