Determination of the degree of acetylation of chitin materials by 13C CP/MAS NMR spectroscopy

C-13 CP/MAS NMR spectroscopy has been shown to be a powerfill tool to quantify the degree of acetylation of chitin and chitosan. In order to optimise the parameters which afford quantitative C-13 cross-polarisation magic-angle spinning NMR spectra, a detailed relaxation study has been carried out on selected chitin and deacetylated chitin samples. A relaxation delay of 5 s and a contact time of 1 ms have been found to yield quantitative NMR spectra of samples with deacetylation degree values of 0.68 and 0.16. The measured spin-lattice relaxation times in the rotating frame, T-1pH, are in the range 6.4-8.9 ms for chitin and 4.3-7.3 ms for deacetylated chitin, while T-CH values for both samples are very similar and range from 0.03 to 0.19 ms. Spin-counting experiments indicate that, within experimental error, all carbon is detected by NMR indicating that the samples studied contain no (or very few) paramagnetic centres. (C) 2001 Elsevier Science B.V, All rights reserved.