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Chitosan
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IntroductionChitosan is the partially deacetylated form of chitin, the glucosamine polysaccharide which forms the exoskeleton of many crustaceans. Chitosan is used in biomedical applications to transport polar drugs. The degree of deacetylation (% DA) is important to its funtionality and biological effects.
While there is currently no USP monograph, there is an EP monograph as well as ASTM standards for chitosan. While EP describes a wet chemistry method for % DA, ASTM F2260 requires 1H nuclear magnetic resonance spectroscopy (NMR). |
Exova TestingExova (WCAS) provides a full range of chemical testing services according to EP and ASTM for chitosan including:
Identification A, B, C, and D |
Degree of DeacetalationThe EP monograph requires the measurement of the UV absorption at 202 nm, comparing the sample to standards of N-acetylglucosamine in water. At this short wavelength, the test method is not very specific. On the other hand, ASTM F2260 uses a much more elaborate, more specific, and more reliable method based on 1H NMR. The ASTM method is based upon work first reported by Varum, et al, Carbohydrate Res., Vol 211, 1991, pp 17-23. The sample must first be depolymerized using nitrous acid in water. Then the 1H NMR spectrum is measured at 90˚C, to further decrease the viscosity. |
Quantitation is achieved by ratioing certain proton signals for chitosan to those for chitose which is formed during depolymerization. In the example spectrum below the signals are assigned as follows: red-a - H1a of reducing-end GlcNAc From these signals, one can calculate the relative number of free glucosamine residues (GlcN) and the relative number of acetylated glucosamine residues(GlcNAc) , and thus the degree of deacetylation. Exova operates a Bruker Avance III 500 MHz system under GMP quality assurance. |
1H NMR Spectrum of Chitosan
