A sample of a chitin was obtained from shells of the shrimp Xiphopenaeus kroyeri by demineralization and deproteinization processes. This sample of native a chitin (NC) was dissolved in concentrated phosphoric acid and recovered by precipitation in an alkaline aqueous solution, giving rise to a sample named PC. Solid-state carbon-13 nuclear magnetic resonance (C-13-NMR), X-ray diffraction, and atomic force microscopy (A-FM) techniques were used to compare both samples and to investigate structural changes in a chitin under the action of phosphoric acid. C-13-NMR experiments and X-ray diffraction results revealed a high crystalline order in both samples. Structural differences were due to the higher distance between adjacent chains along the b axis and the consequent decrease in the number of intermolecular hydrogen bonds in the sample recovered from solution. While remarkable supramolecular differences could be observed in the fibrillar crystals of the NC sample, the PC sample was characterized by only one type of morphology. (C) 2002 John Wiley & Sons, Inc.