A Practical Method for the Determination of Degree of Substitution in Sodium Carboxymethyl Starch

This paper reports on a practical headspace gas chromatographic method (HS-GC) for rapid determination of degree of substitution (DS) in sodium carboxymethyl starch (Na-CMS). After Na-CMS was acidified by hydrochloric acid (HCl) solution, the supernatant of the solution was added to a bicarbonate solution in a closed headspace vial. Thus, the remaining HCl reacts with bicarbonate to form carbon dioxide gas and thus was measured by HS-GC. The result showed that the Na-CMS was completely converted to H-CMS within 45 min at a room temperature when a small sample size (= 0.5 g) was used by acidification pretreatment. The present method has a good measurement precision (the relative standard deviation < 3.25%) and accuracy (the relative difference < 5.46%, compared to the data measured by the reference method) on the determination of DS in Na-CMS. The present method is simple, practical, and suitable for the use in the carboxymethyl starch related research and applications.