Identifying important differences in mass spectra generated by secondary ion mass spectrometry (TOF-SIMS) in a tribochemical study

Abstract

In order to better understand the lubricating properties of diesel fuel, species that were present on tribological surfaces were investigated using secondary ion time-of-flight mass spectrometry (TOF–SIMS). Traditionally, only certain species that are expected to be present at the interface are investigated and their presence or absence is used to make conclusions regarding the mechanism of lubrication. In this work, an alternative and complementary approach to data analysis and interpretation is proposed, previously demonstrated for TOF–SIMS and based on multivariate analysis methods, where the mass spectral data are investigated more comprehensively. The main objective was to interpret variation within and between different areas of a tested surface and ultimately to contribute to the understanding of the tribochemical reactions that occur at the interface. The validity of this approach was confirmed when the palmitate ion (which would normally be targeted) was shown to contribute significantly (together with other ions) to chemical differences between scratched and unscratched areas of the surface.