The molecules can be deliberately labeled with stable isotopes, in one or more positions, and since they are minimally discriminated in metabolic processes, may be used as a tracer in chemical and biological studies.
Isotopes of Carbon
The 13C has applications in medicine, the measurement of the concentration by mass spectrometric allows us to estimate the absorption capacity of different carbon isotopes of different living organisms and different tissues
The isotopes of a compound have the same number of protons but a different number of neutrons. The isotope 12C is the form of carbon most commonly present in nature (constitutes approximately 98.9% of total carbon) and has 6 protons and 6 neutrons, from which the conventional value of 12 attributed to its total mass. The carbon isotope 13C, which has 7 neutrons (one more of the isotope 12C) .1 represents about 1% of the total carbon. With the method of the isotopes is determined exactly at what relationship among them are these two isotopes (13C/12C).
This allows the study of many case because the 13C can be easily distributed in all body tissues.
In medicine, it is often used for the diagnosis of bacterial infections
Isotopes of Hydrogen / Oxygen
Heavy water is water containing a significant percentage of deuterium isotope of hydrogen, both as deuterium oxide, D2O or 2H2O, or as deuterium oxide and uncle, HDO or 1H2HO. Physically and chemically, is similar to water, H2O, in water, the ratio of deuterium to hydrogen is about 156 ppm.
The heavy water is used as part of a mixture with H218O for a common test and fail the average metabolic rate in humans and in animals that perform their normal activities. This metabolic test is usually called “doubly labeled water test”.