Stable Isotopes in Non-ruminant Studies

The scientific areas that make use of stable isotopes result of the spectacular
advancement in physics and chemistry performed in the first half of the twentieth century. In
the 50 years following, the application of stable isotopes expanded to Hydrology,
Cosmochemistry, Geochemistry, Petrology and Oceanography. Recently, new areas were
awarded with the use of the technique: Atmospheric and Planetary Sciences, Microbiology,
Agronomy, Plant Physiology, Ecology, Forensic Science, Soil Science, Archaeology,
Anthropology, Medicine, Extraterrestrial Science and Meteorites (CRISS, 1999; FAURE &
MENSING, 2005).
This expansion is the result of modernization and analytical capacity of the mass
spectrometer (main equipment) and peripherals to increase the number of analyzes with high
level of accuracy in the shortest time.
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The isotopic nomenclature is expressed by , where is the chemical element,
A reflects the mass number in atomic mass units, and Z the number of protons, so that A = Z
+ N, where N is the number of neutrons.
The carbon chemical element, for example (Table 1), has only two stable isotopes;
, being that the carbon-12 is the lightest and most abundant among them, and
they differ by the existence of one additional neutron in the nucleus. The isotopic molecules
12CO2 and 13CO2 are not differentiated by the biological membranes of plant or animal origin,
that is, the small hidden subtlety in the nucleus is not detected, making the carbon isotopes
excellent tracers at level of natural variation or enriched compounds, which is extended to
other bioelements.
There are currently more than 2500 different known isotopes in 110 different
chemical elements with 264 stable isotopes (CRISS, 1999). In biological sciences and related
disciplines, the main chemical elements of interest are the bioelements formed by CHON'S,
which are part of the carbohydrate, lipids, proteins, amino acids and nucleic acids (DNA,
RNA) structure, and are responsible for more than 90% of all living tissues. The main stable
isotopes of bioelements are explicit in Table 1.