In thisPCAcalculation,theloadingplotsaredirectlyrelatedto
the wavenumbers.Theyindicatethespectralfeaturesthathavean
important contributiontotheprincipalcomponents,inother
words,theoneswhichinfluence thescoreplots. Fig. 2 showsthe
loading plotsofPC1andPC2andtheRamanCHstretchingregion
of fivesamplesrepresentativeofthedifferentchemicalfamilies.
A highcontributionofthe2845–2910cm−1 region (Aon Fig. 2) to
PC1 underlinesitsimportantroleintheexploitedvariance.This
might berelatedtothehighintensityoftheoilsspectrainthis
region (highPC1contributiononthescoreploton Fig. 4) andthe
weakintensityofthegluesspectra(verylowPC1contributionon
the scoreploton Fig. 4) forinstance.Around3080cm−1 (B on
Fig. 2), onefeaturespecific tothediterpenicresinsspectrahasa
positiveimportantcontributiontoPC2andalowandnegative
contribution toPC1.Thiscanexplainthedistributionofthe
diterpenicresinsonthescoreplot.Anotherpointthatcanbe
highlighted istheimportantcontributiontobothPC1andPC2of
the 2740–2800cm−1 region andthe3100–3184cm−1 region (Con