Fig. 5.

The spectrum of sphingomyelin measured by ATR-FTIR and mid-IR PAM. The vertical lines indicate the main absorption points, showing a good match between the two imaging modalities (difference $<2{\mathrm{cm}}^{-1}$). The difference between the two spectra at $\sim 3300{\mathrm{cm}}^{-1}$ may be due to the residual solvent contribution that was not completely subtracted in FTIR.