Semi-quantitative characterisation of binary salt mixtures with static secondary ion mass spectrometry (S-SIMS)

The use of static secondary ion mass spectrometry for the semi-quantitative characterisation of major components by means of molecule specific ion signals has been investigated for binary salts. The calibration of the peak intensities as a function of the local concentration has been based on reference mixtures. The preparation of the mixtures has been proven to be a major bottleneck. Five different approaches have been tried out. Fast freezing with subsequent cryo-lyophylisation is the preferred method to obtain adequate molecular mixtures for the empirical calibration of relative peak intensities in S-SIMS as a function of the local concentration. The applicability has been verified in two different laboratories and three instrumental S-SIMS configurations. Monoatomic as well as polyatomic primary ions have been used. Specifically, comparative work involved the use of Ga+ primary ions in a time-of-flight (TOF) S-SIMS and ReO4− polyatomic projectiles in an ion trap and a triple quadrupole instrument, used in the single mass selection mode. In all cases, the local content can be determined with an experimental uncertainty of 10-20% using the molecular (adduct) ion signal intensities in either the positive or negative ion detection mode.