Chitosan is made from chitin by deacetylation. Chitin is naturally found in the exoskeletons of arthropods and in fungi. It is the second most abundant natural polymer on earth after cellulose and is structurally very similar to cellulose. However, each subunit of chitin contains an acetyl amine group which allows additional hydrogen bonding between polymer chains and provides additional strength.
Unlike chitin, chitosan is soluble in acidic aqueous media. Chitosan is used in a number of industries such as agriculture, waste treatment, food/beverage, cosmetics, and biomedical industries. Chitosan can be further chemically modified by reaction of the amine or other functional groups to produce various chitosan derivatives.
Chitosan is biodegradable, non-toxic, anti-microbial, and renewable which makes it very useful in the biomedical field. Properties such as degree of deacetylation and molar mass are related to chitosan’s performance and these can be determined using 1H-NMR (ASTM F2103)and SEC-MALS (ASTM F2602). Determination of these values associated with the polymer’s characteristics is necessary to ensure a safe and effective product.
There are a number of analytical approaches that can be used in order to characterize chitosans and their derivatives. Two of the most commonly used methods are nuclear magnetic resonance (NMR) and size exclusion chromatography with multi-angle light scattering detection (SEC-MALS).
Nuclear Magnetic Resonance Spectroscopy (1H-NMR) determines the degree of deacetylation of a chitosan sample. The degree of deacetylation is related to performance characteristics of the polymer, such as the ability of the polymer to gel and its solubility (ASTM F2103). In NMR analysis, the instrument compares the number of protons associated with acetyl groups of N-acetylglucosamine subunits with those found in the total polymer backbone, and a comparison value is given. For instance, if one out of every three subunits is acetylated (33% of the subunits), then the degree of deacetylation value would be (100% – 33% = 66%) or 0.66.
Size Exclusion Chromatography with Multi-Angle Light Scattering (SEC-MALS) detection estimates the molar mass of a sample in solution. The molar mass of a particular chitosan sample has a direct effect on the viscosity. In order to ensure that a final product will meet established viscosity requirements it is necessary to test it in this manner. This analytical technique can also be used to determine the distribution of the molar mass of a sample, which is known as polydispersity. Commercial chitosans typically have polydispersity values between 1.5 and 3.0 (ASTM F2103).
Chitosan has a wide variety of applications to include: