Chitin characterization by SEM, FTIR, XRD, and 13C cross polarization/mass angle spinning NMR

The full characterization of chitin obtained from squid, shrimp, prawn, lobsters, and king crab is reported. Elemental analysis, including metals such as Ca, Mg, Zn, Cd, Hg, Cr, Mn, Cu, and Pb, was performed, which is quite relevant because the skeleton composition is slightly different for each species. The morphology was studied by means of TEM and their compositions were determined by energy-dispersive X-ray analysis. C-13 cross polarization/magic angle spinning NMR was applied to determine the chemical shift of all the carbons and the difference between them. Chitin was isolated by using chemical methods, alternating hydrochloric acid and sodium hydroxide. The alpha-chitin from shrimp, prawn, lobsters, and king crabs showed two signals at 73.7 and 75.6 ppm. Meanwhile, the beta-chitin from squid exhibited one signal at 75.2 ppm. FTIR studies were used to analyze a-chitin from shrimp and beta-chitin from squid. The a-chitin exhibited amide I vibration modes at 1660 and 1627 cm(-1), whereas the beta-chitin showed one band at 1656 cm(-1). X-ray diffraction showed that alpha-chitin is orthorhombic (a = 4.74 Angstrom, b = 18.86 Angstrom, and c 10.32 Angstrom) and beta-chitin had a monoclinic dihydrated form (a = 4.80 Angstrom, b = 10.40 Angstrom, c = 11.10 Angstrom, and beta = 97). (C) 2004 Wiley Periodicals, Inc.