For my dissertation I have been looking at the biodegradation potential of Galleria mellonella waxworm homogenate on High Density Polyethylene. Samples were kept in two different treatments over a period of 3 weeks. From the FTIR results it's clear that the baseline absorbance increases in both treatments between ~1,700cm-1 and 1,000cm-1 towards the end of the experiment. Spectrophotometry is fairly new to me so I'm not sure whether this is a significant change worth exploring in my discussion and if so, where I can find accessible literature to explain it. Thanks in advance.
Dear Tilly,
The change appeared in FTIR analysis during three weeks is noticeable for degradation of HDPE. I have attached one article and one book which on page 493 the FTIR peaks of HDPE has been mentioned in details. I hope it would be useful.
It is more common to display FTIR analysis according to transmittance.
Mina Karimi-Avargani Thank you so much, these are really useful papers
There does seem to a variation in overall spectrum intensity - you would not expect the C-H peaks around 2900 to change too much, but it also might be that you are observing some oxidation as evidence by carbonyl features around 1700.
How are the spectra taken? Transmission mode or with an ATR accessory?
You can correct for variation in the baseline using an internal reference peak: For polyolefin degradation studies, this is achieved by reporting the "carbonyl index" - this is the ratio of the carbonyl feature (~1714 cm^-1) and a reference peak which does not significantly chemically change throughout the experiment (therefore variation in intensity the spectrum is attributed to the collection or pathlength). Typically a C-H peak is used for reference.
e.g. Ci=[Abs@1714]/[Abs@2920]
For oxidation processes, you would expect Ci to increase. If carbonyl products are being consumed in your experiment you might expect to see a reduction in Ci.
I would deviate slightly from Mina Karimi-Avargani - transmittance is useful for assigning peaks in FT-IR. However, absorbance is proportional to concentration and so must be used for a quantitative approach.
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