Identifying changes in user spectrum compared to library - degradation/oxidation estimate

[ardcarvalho]

I've been thinking in a way to extract more information in a spectra that could be helpfull to estimate degradation or distubance to virgin plastics.

The idea is to implement an advanced parameter in the app that provides information about differences in the user spectrum to the overall library. It has been tought as a within-'polymer class' analysis and we can start with the polyethylene. I propose the following steps:

1. Round spectra to unit to speed the process
2. Pre-process: baseline correction, normalization by the sum and scaling (Pareto scaling?)
3. Eliminate wavenumbers inherent to PE (mainly methylene vibrations in FTIR) - Finally we'll be working with the wavenumbers ranges 800-1200 cm-1, 1500-1900 cm-1 and 3000-3400 cm-1.
4. Run a PCA to identify the spectral regions related with the most variance in spectra.
5. Interpret these regions - my guess is that they will be related with oxidation process, i.e. carbonyl and hydroxyl groups.
6. Estimate in which percentile of all spectra variability the analysed spectrum is: this information might be useful to the user to estimate how oxydyzed their microplastic is (therefore how degraded it is?!)

This will be rather a relative index than an absolute one, and it 's part of the "multivariate analysis tools" that I would like to implement in OS.
Totally open to discuss!

PS: I was inspired by a work that I done with microplastics collected in different environmental conditions (under revision)