How does iodine affect starch?
“Iodine is a common general stain used in thin-layer chromatography. It is also used in the Gram stain as a mordant, after the sample is treated with crystal violet. In particular, iodine forms an intense blue complex with the glucose polymers starch andglycogen. Many applications rely on this property: – Iodometry. The concentration of an oxidant can be determined by adding it to an excess of iodide with a little free iodine, to destroy elemental iodine/triiodide as a result of oxidation by the oxidant. A starch indicator is then used as the indicator close to the end-point, in order to increase the visual contrast (dark blue becomes colorless, instead of the yellow of dilute triiodide becoming colorless). – An Iodine test may be used to test a sample substance for the presence of starch. – The Iodine clock reaction is an extension of the techniques in iodometry. – Iodine solutions are used in counterfeit banknote detection pens; the premise being that counterfeit banknotes made using
