Matrix effects SIMS spectra

A related matrix effect of considerable analytical interest is the enhancement in absolute ion yield sometimes observed under conditions of high dilution in a solid matrix (22). Comparison of the SIMS spectrum of a neat pyrilium salt with that of the same salt diluted 1000-fold in NH Cl shows that the intact cation signal is observed in about three times greater abundance for the NH Cl-diluted sample. The threefold increase is observed even when the absolute amount of salt analyzed in the dilute sample is one thousand times less than that in the neat sample. An additional aspect of this experiment is the persistence of the enhanced signal. Ion bombardment yields products for one day in the NH Cl matrix, but for only about one hour in the neat sample under identical conditions. Effective desorption of ammonium chloride, which entrains analyte, is one way of accounting for these observations. 

In the same study, an unexpected result was observed in the daughter spectrum of the intact cation (m/z 162) from carnitine (see Matrix effects, above). The base peak in SIMS MS/MS is m/z 103, corresponding to loss of trimethylamine by rearrangement, while the same ion in the SIMS survey spectrum is nearly absent. This is a striking case of different behavior between SIMS and gas... 

Another area of SIMS that has received a great deal of attention is the study of simple inorganic salts. Marien and De Pauw (92) have looked at the ion-beam-induced effects in SIMS spectra. It is clear that under high ion fluxes significant damage to the surface occurs, with the resulting complication of the spectrum. FAB, or liquid-matrix SIMS, is free of this effect but has the equivalent complication of reactions with the matrix, as discussed previously. 

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