An IR spectrum can have multiple peaks with varying intensities resulting from the stretching and bending vibrations of the different bonds.

Strong signals result from efficient IR absorptions of bonds with large dipole moments. Weak peaks arise from IR absorptions of bonds with small dipole moments.

The intensity of an IR peak depends on sample concentration, the number of IR-active bonds and the dipole moment.

An increase in the sample's concentration increases the number of absorbing groups, thereby enhancing the peak intensities in the IR spectrum.

For example, a highly concentrated sample of alkane has more C–H bonds and shows stronger absorption peaks than a sample with a lower concentration and comparatively fewer C–H bonds.