Dear all,
After recovering my lignin powder from my biomass, I dried it at 60 °C, under vacuum conditions, for 48 h.
Then, I run an ATR-FTIR with 128 scans and a resolution of 2 cm-1. I obtained the spectrum attached.
I found it very strange because all the peaks are in low intensity and the hydroxyl peak is very low while wide. Moreover, this baseline shift increasing in the direction of the fingerprint seems different from every spectrum of lignin I saw before. Does anybody have any suggestion to explain this behavior?
In my impression, it seems like the sample still has much water....
1. I often get very broad peaks in lignin FTIR. It is likely due to alteration in the structure of lignin while extracting it from biomass. So, there is nothing much that can be done I guess.
2. However, the baseline shift is quite unusual. Please check if (a) baseline correction and (b) ATR or other applicable correction is missing in your analysis.
1) You have measured on an ATR-FTIR and the IR light does not go through the sample with ATR but bounces on your sample a couple of times. The IR light penetrates in your sample with every bounce (but does not go through it). Therefore, IR light with lower wavenumbers will penetrate more deep in the sample. Thus, peaks at 4000 cm-1 will appear much less intense than peaks at 400 cm-1.
With transmission-FTIR, peaks at 4000 cm-1 will appear with much higher intensity than when you measure the exact sample sample with ATR-FTIR but you will need to use KBr pellets while this work is avoided by ATR.
A visual and clear explanation can be found here: https://www.youtube.com/watch?v=QW2uh1BQuGw
2) While it seems that your lignin sample contains a lot of water, I do think you should perform a baseline correction since this will show that your sample does not contain a lot of water.
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