Starting point SIMS is a different type of analytical technique than many others (such as PIXE or EMPA). The important difference here is that there exists no theory to predict the count rate one will measure for some element in a given geological (or other) matrix at a given concentration. In some cases, for example, simply adding a few percent of iron to a sample will change dramatically the count rate for an element.
From the first applications of SIMS to Earth Sciences, few decades ago, there has been the problem of converting the measured signal intensity to concentrations. At best, a standard of the same major-element composition as the unknown could be used to calibrate the signal, but many times such a material is not available. The question then arises: "How close must a standard be to the chemistry and structure of the unknown material?" The intimate knowledge of how secondary ion intensities vary with abundance and sample chemistry is essential for anyone operating a SIMS lab. in the Earth Sciences.
Interferences in the secondary-ion mass spectra represent a further inherent drawback of SIMS, which has hampered its direct use in complex matrixes such as minerals or rocks. In many cases, the isobars (molecular, oxide, doubly- or multiply charged ions, etc..) contribute for the most part to the secondary-ion currents at some mass numbers. The removal or correction of such interferences represents a pre-requisite to the application of quantitative SIMS.
