Carbon 13 (13c) is a natural, stable isotope of carbon with a nucleus consisting of six protons and seven neutrons. As one of the environmental isotopes, it constitutes 1.1% of all-natural carbon on Earth.
Carbon 13 Detection by mass spectrometry
The mass spectrum of an organic compound usually consists of a small peak of a mass unit greater than the apparent molecular ion peak (M) of the entire molecule. This is called the M + 1 peak and comes from some molecules that have a 13C atom in place of 12C. An atom containing a carbon atom is estimated to contain approximately 1.1% of the M + 1 peak in size of the M peak, since 1.1% of the atoms are 13C rather than 12C. Similarly, an atom consisting of two carbon atoms is expected to have a M + 1 peak of about 2.2% of the size of the M peak, since the possibility of a 13C atom in any given atom is double the previous one.
In the above, the chemistry and mathematics have been explain, although it can be effectively used to assign the number of carbon atoms in organic molecules. The result should be rounded to the nearest in the following formula:
C = number of atoms
X = amplitude of M ion peak
Y = M + 1 amplitude of ion peak
13C-enriched compounds are used in the investigation of metabolic processes by mass spectrometry. Such compounds are safe because they are not radioactive. 13C is used to quantify proteins. An important application is “stable isotope labeling with amino acids in cell culture” (SILAC). The analysis in these tests is usually carried out by isotope ratio mass spectrometry at 13C and 12C ratios.
The ratio of 13C to 12C is slightly higher in plants using C4 carbon fixation than in plants using C13 carbon fixation. Because the different isotope ratios of the two plants are spread through the food chain, it is possible to determine whether the main diet of a human or other animal consists mainly of C13 plants or C14 plants by measuring their collagen and other isotopic signature. The deliberate increase of the 13C ratio in food is the concept of i-food, a proposed way to increase longevity.
Uses of Carbon 13
Because of differential intake in plants and marine carbonates of 13C, it is possible to use these isotopic signatures in earth science. Biological processes prefer the low-mass isotope by a kinetic fraction. In aqueous geochemistry, the source of water can be determined by analyzing the 13C value of carbonaceous material found in surface and groundwater. The 13C values obtained from the weather, carbonate and plant are all different. In biology, the ratio of carbon-13 and carbon-12 isotopes in plant tissues varies depending on the type of plant photosynthesis and can be used to determine what kind of plants the animals use. In geology, the 13C / 12C ratio is used to identify the layer of sedimentary rocks created during Permian extinction when the 252 Ma ratio is suddenly 1% changed. More information on the use of the 13C / 12C ratio in science can be found in the article about isotopic signatures.
Carbon 13 has a non-zero spin quantum number of 1/2, thus allowing the construction of carbon-containing materials to be investigated using carbon-13 nuclear magnetic resonance.
Carbon 13 Urea breath test is the safest and most accurate diagnostic tool for detecting the presence of Helicobacter pylori infection in the stomach. Due to the non-radioactive nature, urea breath test using carbon-13 is preferred to carbon-14 for some vulnerable populations.