Fig. 2.

To monitor the instruments’ sensitivity, the lowest limit of detection (=highest dilution factor) was determined for nine bovine serum album (BSA) peptides (vertical gray lines) before any mass spectrometry imaging (MSI) experiment (a). These instrument sensitivity profiles were compared to the behavior of the corresponding MSI tissue profiles in the principal component analysis (PCA) space for the detection of potential experimental outliers (b, c). The PCA plots also show the most influential m/z signals for each principal component (red arrows) such as m/z 842.521, which is an autolysis product of trypsin, or m/z 229.117, which is the matrix 9-aminoacridine