Molar Masses and Molar Mass Distributions of Chitin and Acid-Hydrolyzed Chitin

Never-dried and dried crab shell chitin and squid pen chitin samples were acid-hydrolyzed in 1 M HCl at 85 °C for up to 2 h. The crystallinities, crystal sizes, and degrees of N-acetylation of the acid-hydrolyzed chitin samples are almost unchanged the same before and after acid hydrolysis. The original and acid-hydrolyzed chitin samples were dissolved in 8% (w/w) lithium chloride/N,N,-dimethylacetamide, and the solutions were subjected to size-exclusion chromatography with multiangle laser-light scattering analysis to determine their molar masses and molar mass distributions. The molar mass of each chitin sample decreases with increasing acid hydrolysis time, and the weight-average degree of polymerization (DP_w) becomes constant after acid hydrolysis for 0.5 to 2 h. However, the DP_w values of the chitin samples after acid hydrolysis for 2 h (DP_w-2h) are different: Never-dried squid pen chitin has the highest DP_w-2h of 1530, whereas the DPw-2h values of other chitin samples are in the range 220-410.