Study Of Coulometric Titration For The Analysis Of Degree Of Deacetylation Of Chitosan

Though many valid analytical methods were proposed for determination of the degree of deacetylation of chitosan, but no one could totally met the demand of simplicity, convenience, low cost, highly automation and satisfactory of accuracy. The coulometric titration was proposed in the paper for application in the analysis of degree of deacetylation of chitosan and satisfactory results were obtained.The routine coulometric titration was primarily employed for determination of the degree of deacetylation of chitosan. The remaining hydrochloric acid in the sample solution reacted with the generated OH- by electrolysis until the titration end-point, the result was obtained by Faraday's law. The results were similar to those from 1H NMR(American Standard Test Method) and the standard deviations were lower than 0.5%. With merit of simplicity, convenience, quickness, high accuracy and precision, automatic detection of titration end-point and low-cost, the proposed method will be useful in the industrial production.The aboved method was improved and a novel method was proposed that was called two-abrupt-change coulometric titration. It based on that the chitosan solution was the mixture of strong acid and weak acid. The protonated amino groups of chitosan could be directly titrated and the potential was indicated by an antimony electrode which could sensitively response to the variation of activity of hydrogen ion in the turbid and viscous chitosan solution. The degree of deacetylation of chitosan was obtained by the difference of electrolysis time between two inflection points in the electrolysis process. The measuring error that was caused by residual acid or alkali in chitosan could be overcome. The method would possess more extensive practicability relative to other methods and also provided a new road for the research of coulometric titration in mixed acids or bases system.The main work is as follows:(1) The degree of deacetylation of chitosan was determined by routine coulometic titration and related formulas were deduced. In addition, the instrument of acid-base coulometric autotitrator of constant current was assembled. Hydrochloric acid was selected as the object of study and the electrolytic conditions, such as: indicating electrode couple, species and concentration of sustainable electrolyte, constant current strength et al, were discussed by series of coulometric titration experiments.(2) According to electrolytic conditions, different chitosan samples were measured by routine coulometric method. Compared with other methods, such as alkali titration, potentiometric titration, UV, 1H NMR and elemental analysis, the accuracy, precision and robustness of the method were evaluated.(3) The principle of two-abrupt-change coulometric titration was constructed for objectly reflected true value of degree of deacetylation of chitosan on the basis of routine coulometric titration. Corresponding formulas were deduced and the instrument was improved. The experimental procedure and adverse effect of residual acid or alkali were studied. Compared with other methods, the accuracy, precision and reliability of the improved method were evaluated and merits and faults of the method were discussed.