In order to establish new discriminating criteria for the studied
substances, a specific methodology based on the bands morphology
and profile, and involving multivariate analyses was set up. It can be
described as follows. The first step consisted in choosing the most
appropriate spectral region to process. Although the most specific
bands are located in the fingerprint region (200–1800 cm−1) of the
spectra, they are weak especially for Raman and therefore most likely
to disappear or be modified in case of a bad signal-to-noise ratio;
with also further complication to study band profiles (Fig. 1). How-
ever, the CH stretching vibration band in the 2900 cm−1 area is the
most intense region on the Raman spectra, and always intense on the
IR ones. Moreover, a detailed comparison of the materials spectra
(Fig. 2) shows some differences between the CH bands shapes.