1. Introduction
Chitosan is typically obtained by partial deacetylation of chitin. The product is a
copolymer of N-acetylglucosamine units and D-glucosamine units. Molar fraction of Nacetylglucosamine
units in the chain, defined as:
(1)
is called the degree of deacetylation (DD), where, n GlcN – average number of D-glucosamine
units, n GlcNAc - average number of N-acetylglucosamine units. In some works, degree
of acetylation is used, DA = 100 – DD. Several methods for determining the degree of
deacetylation have been elaborated, from simple, such as pH-metric titration, UV-Vis spectroscopy
[1], infrared spectroscopy [1, 2], elemental analysis [3], to complex ones, which
require complicated and expensive equipment, such as 1H NMR spectroscopy [4 - 6] and
13C NMR spectroscopy [7, 8]. Within the same method, there are usually many analytical
procedures for performing measurements and calculations and many ways of interpretation
of results. It is obvious that not every research laboratory has an NMR spectrometer.
Moreover, this method, although probably the most precise, is not suitable for routine measurements
of DD due to high costs (deuterated solvents, depreciation of equipment, specialized
staff time) and time-consuming sample preparation procedure. Most laboratories
must work on less advanced, simpler and cheaper techniques. Therefore it is important to
determine which of these methods lead to reliable, reproducible results in line with ‘standard’
by NMR. Indication of such methods is also important in the case of parallel research
conducted by many laboratories (e.g., international projects, collaboration with industrial
research laboratories, etc.) to provide the ability to compare the results. The selected technique
must be precise, accurate, reproducible and inexpensive.