In this way hydrogen, besides the normal element, also gives us deuterium, whose nucleus is formed by one proton and one neutron. Some isotopes are unstable and transform themselves to other elements by a process known as radioactive decay. Others are stable and persist without changing. Regardless, with few exceptions, the most abundant isotope form that occurs in nature is the one of lowest mass, eg. Thus, when we take a naturally occurring nutrient, and substitute a heavy isotope at one of its positions, it results in a molecule that is chemically indistinguishable form the natural or endogenous form, but is slightly heavier.
Mass spectrometers are instruments that can measure small mass differences in molecules.
Thus, by mass spectrometry, we are able to analyze the heavy isotope molecule in the presence of high endogenous concentrations of natural molecules. There are two forms of mass spectrometry that we use in our program . These instruments are distributed around campus in individual labs as well as at the Molecular Structure Facility at Davis. AMS is a rapidly emerging tool for investigation biological systems and arguably the most versatile accelerator in the world is housed at the Center for Accelerator Mass Spectrometry . This form of isotope measurement is only recently developed for bioanalytical tracing but finding immediate application to in vivo human experimentation.