Improving the interpretation of ToF-SIMS measurements on adsorbed proteins using PCA

Analyzing different proteins with time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a big challenge owing to the absence of unique, identifying peaks between the protein spectra. One possibility for improving the interpretation of the protein spectra is the application of principal component analysis (PCA). The proteins fibronectin and collagen and three fibronectin-collagen mixtures, adsorbed on smooth silicon substrates, were analyzed with ToF-SIMS. The intensities of molecular protein fragment signals were used to perform a PCA calculation. It was shown that PCA could clearly distinguish the various protein mixtures. From the loadings, it was possible to draw conclusions about the peak intensity distribution. Furthermore, PCA was found to be an appropriate statistical tool to identify outlier. Copyright (C) 2006 John Wiley & Sons, Ltd.