These secondary ions are extracted from the surface, mass analyzed based on unique mass-to-charge ratio of individual elements, and collected as secondary ion intensities. Since each element (and isotope) in the periodic table has a unique mass-to-charge ratio, this technique can detect every element in the periodic table.
The secondary ion intensities can be converted into concentrations based on analysis of reference standards. By continually monitoring the ions, one can determine the concentration as a function of depth into the sample with minimum distortion to the true in-depth distribution and with very high sensitivity (ppma to ppba).