The use of infrared spectroscopy for characterization of the composition of chitin and chitosan covering the entire range of degree of acetylation (DA) and a wide variety of raw materials is examined further. The ratio of absorbance bands selected was calibrated using H-1 liquid and C-13 CP-MAS solid-state NMR as absolute techniques. LR spectra of the structural units of these polymers validated the choice of baselines and characteristic bands. The bands at 1650 and 1320 cm(-1) were chosen to measure the DA. As internal reference, the intensities at 3450 and 1420 cm(-1) were evaluated. The absorption band ratios involving the reference at 3450 cm(-1) had poorer fit.. The absorption ratio A(1320)/A(1420) shows superior agreement between the absolute and estimated DA-values (DA% = 31.92A(1320)/A(1420) - 12.20; r = 0.990). (C) 2001 Elsevier Science Ltd. All rights reserved.