Substitution degree (Degree of Substitution, DS) Tested
Substitution degree (Degree of Substitution, DS) determines the nature of the CMC, while the distribution of substituent groups also affect the nature of the product. Accurate determination of the DS and the substituent distribution is to optimize the reaction conditions, to determine the nature of the relationship between the structure of the prerequisites.
Carboxymethyl substitution can occur in the glucose unit (AGU) of the 2,3,6-position, there are eight possible structural units (unsubstituted; C2; C3; C6; C2, C3; C2, C6; C3, C6; C2, C3, C6) form the polymer chain. Different distribution of repeating units in the polymer chain may also be different.
One common method of measuring the degree of substitution CMC DS is measured by titration, the sodium CMC into the acid form, and vice versa. The sodium CMC was dispersed in ethanol and hydrochloric acid, with a sodium hydroxide solution of known molarity titration. There is also a back-titration method is generally measured degree of CMC replace the standard method: the sodium hydroxide is added to the unknown amount of CMC acid, anti-titration of excess sodium hydroxide to calculate the DS. Conductance titration DS may be measured more accurately, Yang Hui Zeng put forward infrared spectroscopy can intuitively roughly determine the purity of the sample, in order to determine the need for sample purification purification. Sodium determination is relatively simple, but needs to satisfy a number of prerequisites, CMC require complete conversion to the sodium salt form, but also brings in the synthesis NaCl and sodium chloroacetate need to completely remove. The latter problem is usually solved by the dialysis method, but this is also a problem, for high and low molecular weight, partially substituted molecules easily lost, this will result in errors. CMC may form a precipitate with the salt ions such as copper ions, an excess of copper ions back-titration can also be determined degree of substitution of CMC.
For CMC, with uranyl nitrate solution for precipitation, and then burn the resulting determination of uranium oxide, is an effective method for the determination of the degree of substitution.