Upperpart:loadingplotsoftheprincipalcomponentsPC1andPC2which
account for33.4%and17.1%respectively,ofthetotalvarianceintheFT-Raman
spectra ofthe37referencematerialsstudied.ThelettersA,BandCrefertothree
spectral regionsdescribedinthetext.Lowerpart:CHspectralregionof5different
chemical families:proteins,triterpenoidresins,diterpenoidresins,triglycerides
and polysaccharides.This figure indicateswhichspectralfeaturesoftheRaman
CH regionhaveanimportantcontributiontoPC1andPC2.