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Iodine - Starch test

The Iodine Starch test was developed in 1814. The test involves using iodine and an iodide (usually potassium iodide) in solution. It can detect extremely low levels of starch - the starch granules turning an intense dark blue-black colour.

It's a highly standardized test, and although in routine use for more than 200 years, the chemical mechanism of the reaction is still not known.

A 2016 research project suggested that the test might have similarities with a compound known as the pyrroloperyleneā€“iodine complex.

The crystal structure of the pyrroloperyleneā€“iodine complex (with a formula close to pyrroloperyleneā€“I2.2) has been solved. The structure contains infinite polyiodide chains, the Raman spectrum of which resembles that of the famous starchā€“iodine complex, thus casting light on a historical puzzle."

Angewandte Chenie , Volume 55, Issue 28

Note: The test is also used in reverse, to detect low levels of iodine

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