Iodine test

The iodine sample ( iodine -starch reaction ) is a chemical process for the detection of starch using an iodine - containing solution. It usually either an iodine - potassium iodide solution ( Lugol's solution) or a tincture of iodine is (alcoholic solution of elemental iodine ) is used, which is dripped onto a solid sample or added to a sample solution. The result is the " Iodstärke ", an inclusion, which - depending on the concentration of the iodine solution used - a deep blue, violet-blue to black coloration.

Secondly, the iodine sample is also applicable for the detection of iodine by the use of a starch solution. It rarely is used for the detection of iodide, although this is possible since the typical color does not occur in the absence of iodide. The picture shows the results of two Iodproben are seen in beer brewing. In the two left depressions in the mash thickness available yet. In the two right-hand grooves, the starch is completely converted.

Chemical background

The presence of amylose in the starch has a helical conformation with a channel-like cavity in the center. In these, Polyiodidketten can (I3, I5, I7, I9 - store ). In those composed of I2 molecules chains, which attach themselves to an existing iodide ion in the solution, all seven valence electrons of iodine atom are delocalized. This reduces the excitation energy of the valence electrons, so they absorb light in the longer wavelength region and to appear complementary blue - black. This coloration is exploited in analytical methods of Iodometry.

When diluting or heating breaks down the inclusion compound. By the addition of ethanol or carbon disulphide, the iodide ions are dissolved out from the helix.