The relatively high ionization probability for many elements
during sputtering, combined with localization of the secondary ions
either by the use of a focused primary ion beam (ion microprobe) or
by a direct ion imaging system (ion microscope), allows
measurements of isotope ratios for both major and minor elements in
small (nanogram) particles as well as in situ mapping of isotopic
and trace element abundances in thin sections or individual grains.
While the lateral spatial resolution can be sub-micron for major
element mapping, it is more typically in the few to 
25 
m
range for most isotopic and trace element measurements. However,
since the vast majority of sputtered ions originate from the
instantaneous sample surface (which is continually eroded during
analysis), spatial resolution in the vertical dimension can be very
good (tens of nm), enabling depth profiling of tracer isotopes or
elements in natural samples and experimental run products (e.g.,
diffusion studies).