3.2.1. Effect of acid concentration and temperature on glucosamine yield
Chitosan was first dissolved in acetic acid to aid its dispersion in the concentrated HCl solutions. The dispersed chitosan was then hydrolyzed at two different temperatures. The glucosamine content in the hydrolysate solution was analyzed and plotted against hydrolysis time. Fig. 3 shows the glucosamine yield during the hydrolysis process with respect to hydrolysis time at various acid concentrations and temperatures. As shown in Fig. 3, using 8 M HCl, after 8 h of hydrolysis, chitosan is not fully hydrolyzed into glucosamine, and less than 40% glucosamine yield is detected at 90 ◦C. The glucosamine yield reaches98% using a digestion condition of 10 M HCl and 105 ◦C in 6 h. We also observed similar recovery using 12 M HCl and 90 ◦C in 6 h. Based on these results, hydrolysis conditions of 10 M HCl, 105 ◦C,and six hour duration were selected as the optimum conditions for method validation. The hydrolysis conditions of 12 M HCl and 105 ◦C result in complete glucosamine conversion in two hours, but the endpoint is difficult to control because glucosamine decomposes rapidly under these conditions (Fig. 3).