A comparison of some methods for the determination of the degree of substitution of carboxymethyl starch.

摘要

The degree of substitution (DS) markedly affects the properties of sodium carboxymethyl starch (Na-CMS). In this study, Na-CMS samples with different DS, prepared from potato and corn starch, were synthesized in an ethanol/water mixture and their DS was determined using 3 methods: direct titration of the acid form of the carboxymethyl starch (H-CMS); Cu salt precipitation; and back titration. It was found that direct titration gave smaller DS values, while the Cu salt precipitation method gave higher DS values than the back titration method, which was found to be the most accurate. DS values achieved by the 3 methods were similar at lower DS, while at higher values, discrepancies were more pronounced. Under the same experimental conditions, the CMS obtained from corn starch had a higher DS than that obtained from potato starch. Overall, discrepancies between DS values obtained by the 3 techniques were smallest for the CMS samples synthesized from corn starch.