Fig. 1 shows the chemical identification of nanoscale sample contaminations with nano-FTIR. In the topography image (left), a small sample contaminant (B) can be found next to a thin film of PMMA (A) on a Si substrate (dark region). In the mechanical phase image (middle) the contrast already indicates that the particle consists of a different material than the film and the substrate. Comparing the nano-FTIR absorption spectra at the positions A and B (right panel) with standard IR databases reveals the chemical identity of the film and the particle. Each spectrum was taken in 7 minutes with a spectral resolution of 13 cm-1.