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

C-13 CP/MAS NMR spectroscopy has been shown to be a powerfill tool to quant ify the degree of acetylation of chitin and chitosan. In order to optimise the parameters which afford quantitative C-13 cross-polarisation magic-angl e 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 spect ra of samples with deacetylation degree values of 0.68 and 0.16. The measur ed spin-lattice relaxation times in the rotating frame, T-1pH, are in the r ange 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 ca rbon is detected by NMR indicating that the samples studied contain no (or very few) paramagnetic centres. (C) 2001 Elsevier Science B.V, All rights r eserved.