同时测定羧甲基甲壳素的羧基取代度和脱乙酰度的方法

Simultaneous Determination of the Degree of Substitution of Carboxyl and Amino Groups of Water-soluble Carboxymethyl Chitin/chitosan Carboxyl Group

羧甲基甲壳素在造纸行业作为增强剂,保湿剂和天然抑菌剂,广泛用于生产各类特种纸。论文采用传统方法对甲壳素进行非均相脱乙酰反应和羧甲基醚化反应,制备了羧甲基甲壳素,通过电导率滴定法检测其取代度。与文献介绍的加碱电导法相比,通过先加碱溶样品,标准稀盐酸滴定和电导率的一阶微分处理方式,更加方便准确地确定电导率突变点对应的体积(V1,V2和V3),避免了原方法中易出现的样品絮凝和沉降现象,促进样晶和稀盐酸的中和反应均匀进行,提高了电导法的准确度和精确度。五次测试结果表明,该电导滴定法的标准偏差不超过2.2%,和13C-NMR参考方法相比,最大差值绝对值不超过8%。借助羧甲基甲壳素的红外光谱图,我们发现3445cm^-1处的峰受到水分的干扰;1655cm^-1的峰是酰胺NH弯曲振动峰与C=0拉伸振动峰的重叠峰,表明红外光谱不适合用于定量分析羧甲基甲壳素的脱乙酰度。

Carboxymethyl chitin, as a reinforcing agent, moisturizer and natural bacteriostatic agent, is widely adopted in producing various types of specialty papers. In this paper, chitin was used to prepare carboxymethyl chitin through heterogeneous deacetylation and carboxymethyl etherification reaction, and its degree of substitution was determined by conductivity titration with addition of dilute hydrochloric acid. Compared with the conductivity titration with addition of alkali introduced in the literature, it is more convenient and accurate to find the consumed volume of HC1 corresponding to the conductivity turning point ( VI , V2 and V3 ) by first adding alkali aqueous in order to dissolve sample, titrating with standard dilute hydrochloric acid and analyzing the conductivity curve with first-order differential treatment. The flocculation and sedimentation of the carboxymethyl chitin polymer could be avoided by using this new method. However, such a phenomenon is always found out in the original method with alkali addition. Thus, the uniform neutralization reaction is achieved, and results in the improvement of accuracy and precision of the present method. Five test results show that the standard deviation of the conductivity titration does not exceed 2. 2 %, and the Maximum difference absolute value of 13C-NMR reference method does not exceed 8 %. By means of the infrared spectrum characterization of carboxymethyl chitin, we discover that the peak at 3445 cm^-1 is disturbed by moisture and the peak at 1655cm^-1 is due to the overlapping of amide NH bending and C = 0 stretching of carboxymethyl group, which indicates FT-IR spectra is not suitable for quantitative analysis of the degree of deacetylation of the discussed water-soluble carboxymethyl chitosan.