Lugol's iodine

• Lugol's solution
• Potassium tri-iodide (IUPAC)

Brown liquid

Liquid

1.12 g · cm -3

23 hPa (at 20 ° C)

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Iodine - potassium iodide solution (in lab jargon iodine Iodkalium, often synonymous with Lugol solution used) is a solution of iodine in water. Elemental iodine is poorly soluble in water. However, if already dissolved iodide ions are present, the iodine to form polyiodide solves:

Therefore potassium iodide is added.

Iodine is much more soluble in ethanol, but sometimes ethanol is undesirable as the solvent because it is flammable and can evaporate quickly and lead to unwanted side reactions. Is iodine dissolved in alcohol, the solution is denoted as tincture of iodine.

Applications

An iodine - potassium iodide solution is used for various purposes, for example in analytical chemistry and medicine. Examples are:

• For Gram stain in microbiology, usually with Lugol solution ( see below)
• To Chitinnachweis in microscopy or in food chemistry,
• For detecting starch, usually with the Lugol solution ( see below),
• For the detection of alkaloids with Bouchardats or Wagner's reagent,
• As a disinfectant,
• As a standard solution in the iodometry
• Pathologists use the solution to amyloidosis (eg Alzheimer's disease) to prove at autopsy,
• Commitment to the so-called Plummern in hyperthyroidism,
• For fixation and preservation of phytoplankton samples.
• For the etching of gold

Lugol's solution

The Lugol's solution (Latin Solutio Lugoli ) is an iodine - potassium iodide solution ( brownish red color and characteristic odor ) with a 1:2 ratio of iodine to potassium iodide in water, which is also offered in the trade. It is named after the French physician Jean Lugol Guillaume (1786-1851) appointed who invented it in 1835.

Mechanism of the proof strength

The strength of evidence is based on a characteristic and highly sensitive color reaction. The I5 - ions can intercalate into the starch molecules. The inclusion compound has in amylose and amylopectin, a blue, a brown-violet color. The difference is because the amylose molecules are helically twisted, thereby changing the absorption of light.