Of What Use is a Relative Abundance?
The relative abundance of the +1 profile arises primarily, but not entirely, from the presence of a single 13C atom in place of a 12C atom in the ion. Each C atom has a 1.1% chance of being a 13C atom. An ion with 10 C atoms would have a +1 profile abundance of 11% due to 13C atoms alone. In fact, the relative abundance of the +1 profile has long been used to estimate the number of C atoms in an ion. Likewise the number of Cl, Br, or S atoms has been estimated from the relative abundance of the +2 profile. Mass Peak Profiling from Selected Ion Recording Data (MPPSIRD) provides more accurate relative abundances than conventional full scanning. Hence, relative abundances become even more useful for determining the numbers of atoms of different elements in an ion. Note that in the absence of mass interferences, one can use low mass resolution to obtain accurate relative abundances. This is important when trace levels of compounds are studied and the +2 relative abundance is less than 1%.
