Trace substances, biological monitoring

Tracers are materials that are used as markers to show the location of a substance or to follow the pathway of a substance in a chemical reaction or physical process. Such tracers have to show the same physical and chemical behavior in the system under observation as the material that is actually observed. Radioactive isotopes are ideal tracers for a nonradioactive isotope which has to be traced because they show the same chemical behavior like the nonradioactive material. It is the activity of the radioisotope that is monitored to follow the process under investigation. In addition, the amount of radioactive material to be added as a marker can be kept extremely small. This is of great importance if biological processes are investigated because the amount of tracer material can be kept low enough not to interfere in physiological processes. The most important assumption made in the use of radiotracers is that the radioactive material will blend in perfectly with the system under study and that the emitted radiation does not affect any components of the system. 

---