Inhibition of Amylose-Iodine Color Reaction by Alkali

Abstract

The absorption spectra of an amylose-iodine color reaction solution at various pH values were taken over a broad region. The coloration of the amylose-iodine color reaction solution was stable until pH 9.82, but above this pH value the coloration rapidly began to be inhibited. At pH 10.88, the coloration was completely inhibited. At this juncture, it was observed that the amount of the triiode ion, I-3, in the reaction solution decreased as the alkalinity increased. When the addition of iodine was increased, the inhibition due to alkali was proportionally reduced. Even under the acidic condition, when the amount of iodine was decreased, the same inhibition of color was observed as under the alkaline condition. The concentrations of the triiode ion were almost the same under both conditions when the inhibition of the coloration began to appear. From the above results, it is presumed that the inhibition of the amylose-iodine color reaction is caused by a decrease in the amount of the triiode ion needed for the formation of the amylose-iodine complex. This decrease is attributed to the effect of alkali on iodine.