Procedures for interpretation of 2Der/1Der loadings?

jvrijdag's picture

Dear All,

I am investigating the starch and non-starch polysacharide (NSP) composition of grains, therefore I recently started working with IR and chemometrics. After a lot of trail-and-error (preprocessing of spectra, chemometrics software, PCA, etc.), I was delighted to see that during PCA some presumed clusters were formed.

To understand "why" some clusters were formed in PCA score plots, I turned my attention to PC loadings. Unfortunately, here I got slightly lost in interpretation. PC loadings can of course contain both positive and negative values. Also, I mainly used 2Der spectra for PCA, so every band from the original data is represented by 3 bands in the PC loadings.

So far I just picked a couple of large bands on both the positive and negative side of the loading, and tried to interpret/assign them. Since I am dealing with different polysacharides, each of them having complex IR spectra, I would like to interpret the PC loadings as rationally as possible. In the future I would like to purchase/prepare reference polysacharide compounds, but for now the focus is on obtaining as much useful information as possible from the PC loadings.

Is there a certain procedure to interpret such PC loadings from 2Der data? E.g., picking the largest bands (how many, typically?) or bands with certain characteristics, and assuming them to be "central" band of 3 in the 2Der spectra? Are there any data processing techniques for 2Der PC loadings, highlighting the most crucial regions?

Also during PCA of 1Der spectra I obtained useful groupings. Similar to my previous question, are there certain established procedures to interpret PC loadings from 1Der data?

Any help will be appreciated!



P.S.: If this discussion fits better in the "Spectroscopy" Section, please feel free to move it there!