4. Conclusion
Several types of chitin, chitosan and DBC were studied
with FT-IR in order to establish differences in structure and
degree of substitution (and thus degree of conversion).
FT-IR peak analysis confirmed that indeed the desired
reactions had taken place but FT-IR done as suggested in
literature did not provide accurate absolute DA values.
FT-IR DA determinations are clearly dependent upon the
followed method and especially sample form and treatment.
So great care should be taken when assessing the DA value
of chitin by FT-IR measurements, and a calibration with
respect to a direct technique such as 13C NMR should be
performed. This calibration is then only useable for one
certain combination of FT-IR method and sample form. A
formula for the quantitative determination of the degree of
acetylation by FT-IR is proposed in this article. Should one
however want to compare different chitin or chitosan types
qualitatively, FT-IR without calibration may prove to be a
very useful tool for determining differences in DA and
crystalline structure.
For DBC no method for the assessment of the degree of
butyrylation—based on FT-IR measurements—is found in
the literature. Several measurement peaks and reference
peaks were investigated but the results were not conclusive
enough to differentiate between the two studied DBC types.
Comparing with a direct technique such as 13C NMR would
yield a series of calibration curves, thus resulting in relevant
FT-IR measurement and reference peaks. This might be the
subject of further study.