An infrared investigation in relation with chitin and chitosan characterization

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 1H liquid and 13C CP-MAS solid-state NMR as absolute techniques. IR 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 A1320/A1420 shows superior agreement between the absolute and estimated DA-values (DA%=31.92A1320/A1420−12.20; r=0.990).