Institution: | a Department of Chemistry and Biochemistry, CECUL, University of Lisbon, 1749-016, Lisbon, Portugal b Department of Technology of Chemical Industries, National Institute of Engineering and Industrial Technology, 2745-578, Barcarena, Portugal c Department of Chemistry, University of Aveiro, 3810 Aveiro, Portugal |
Abstract: | 13C CP/MAS NMR spectroscopy has been shown to be a powerful tool to quantify the degree of acetylation of chitin and chitosan. In order to optimise the parameters which afford quantitative 13C 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, T1ρH, are in the range 6.4–8.9 ms for chitin and 4.3–7.3 ms for deacetylated chitin, while TCH 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. |