Geological Applications of SIMS

In geology, SIMS is applied mainly to trace element and isotopic analysis rather than surface analysis or depth profiling. Good spatial resolution is desirable, hence the instruments used are generally of the ion probe type, with primary beam focussed to a few μm. The image-forming type of instrument (ion microscope) can also be used, in which case a small part of the image may be selected for ‘spot’ analysis. Molecular interferences necessitate high mass resolution in many geological applications, hence double-focussing magnetic-sector mass spectrometers are favoured in preference to the simpler quadrupole type.