How can the degree of acetylation be determined?
There are different ways to determine the degree of acetylation of chitosans. In the case of chitosan oligomers, the most precise method is mass spectrometry (MS) that measures the molecular weight which can then easily be used to calculate the degree of polymerization and the degree of acetylation of the sample. Importantly, mass spectrometry will not give an average value for DA and DP but will separate the oligomers according to their molecular mass so that the composition of a sample can be determined with accuracy (at least in terms of degrees of polymerization and acetylation, while the pattern of acetylation is more difficult to determine). This is not the case for chitosan polymers where the degree of acetylation determined will always constitute an average value (and no method is available to determine the distribution of molecules in the sample). The most frequently used methods to determine the degree of acetylation of chitosans are potentiometry/titration and nuclear magnetic resonance (NMR) spectroscopy, but many more exist. The former do not require sophisticated and expensive infrastructure, but their accuracy greatly depends on the experience of the performer, leading to large insecurities regarding results. NMR is much more expensive but also much more reliable, it is considered the gold standard for DA analysis.