Table 11.

9.1.2 Acidic conductivity dosing

Modern Spectroscopic Techniques and Applications

DDA calculation gives:

the method described in the literature [77, 78].

equation:

Table 11.

Figure 4.

122

for calculating DD.

The determination of the DD by acid conductometric assay is carried out as follows: a mass of 150 mg of chitosan is dispersed in 200 ml of distilled water; while stirring, the mixture is titrated with 0.1 N HCl solution. Figure 3B shows the evolution of the conductivity of the chitosan solution as a function of the volume of HCl poured. The point of inflection corresponds to the amount of HCl consumed by

DD ¼ ð Þ 203 � V � N =ðm þ 42 � V � NÞ � 100 (9)

the amine groups of chitosan. The DD will be calculated from the following

where N is the normality of the HCI solution (mol/l), V is the volume corresponding to the inflection point as shown in Figure 3B, m is the mass of chitosan (g), and 42 (g/mol) is the difference between the molecular weight of the acetylated monomer and the molecular weight of the deacetylated monomer.

DD ¼ ð Þ 203 � 6:8 � 10 � 3 � 0:1 =ð0:15 þ 42 � 6:8 � 10 � 3 � 0:1Þ � 100

9.2 Determination of the degree of deacetylation by pH-metric determination

The determination of the DD by pH-metric assay was carried out according to

A solution of chitosan was prepared by dissolving a mass of 125 mg of chitosan in a solution of excess HCl (0.1 N) and then neutralizing this solution with sodium hydroxide solution (0.05 N). Figure 4A shows the titration curve of chitosan, and Figure 4B shows the corresponding secondary derivative. From this last curve, the amount of hydrochloric acid necessary to protonate the amine groups is determined. The degree of deacetylation calculated from this method is 77.10%.

The results of the DDA obtained by the different assay methods are shown in

(A) Variation of the pH according to the volume of soda poured for the solution of the chitosan and the solution

of the hydrochloric acid, (B) secondary derivative curve corresponding to the assay.

The average value of DD calculated for the chitosan prepared during this work is 77.32%. So, IR spectroscopy remains the simplest and most economical technique

DD <sup>¼</sup> <sup>77</sup>:30%: (10)

DD values obtained with different assay methods [70].


#### Table 12.

Comparison of DD value measured by different methods [79].
