Abstract
AbstractA simple and rapid ion exchange method is presented for the in situ determination of calcium carboxymethylcellulose (CaCMC) on a cellulose film. The method is based on the ion‐exchange reaction between the calcium ion in CMC and a large quaternary ammonium ion, such as hexadecyltrimethylammonium ion, followed by a second ion exchange reaction in which the quaternary ammonium ion is displaced by 3,9‐bisdimethylaminophenazothionium ion. The development of a blue color allows for the determination of the CaCMC distribution on the film by using a scanning densitometer. The reasons that CMC prefers a relatively large quaternary ammonium ion to the divalent calcium ion are suggested. This method is also applicable for the determination of sodium carboxymethylcellulose film where it is only necessary to carry out the second ion‐exchange reaction. The minimum detection limit for a CaCMC (degree of substitution is 0.7) coating is at least 1 μg/cm2.
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