Applications of Potassium iodide

Potassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic (absorbs water less readily) than sodium iodide, making it easier to work with. Aged and impure samples are yellow because of aerial oxidation of the iodide to elemental iodine.
Potassium iodide is medicinally supplied in 130 mg tablets for emergency purposes. Potassium iodide may also be administered as a "saturated solution of potassium iodide" (SSKI) which in the U.S.P. generic formulation contains 1000 mg of KI per mL of solution. This represents 333 mg KI and about 250 mg iodide (I -) in a typical adult dose of 5 drops, assumed to be ⅓ mL. Because SSKI is a viscous liquid, it is normally assumed to contain 15 drops/milliliter, not 20 drops/milliliter as is often assumed for water. Thus, each drop of U.S.P. SSKI is assumed to contain about 50 mg iodine as iodide, I -. Thus, two (2) drops of U.S.P. SSKI solution is equivalent to one 130 mg KI tablet (100 mg iodide).
Applications
Industry
KI is a precursor to silver iodide (AgI) an important chemical in photography. KI is a component in some disinfectants and hair treatment chemicals. KI is also used as a fluorescence quenching agent in biomedical research, an application that takes advantage of collisional quenching of fluorescent substances by the iodide ion. However, for several fluorophores addition of KI in µM-mM concentrations results in increase of fluorescence intensity, and Iodide acts as fluorescence enhancer. Potassium iodide is a component in the electrolyte of dye sensitized solar cells (DSSC) along with iodine. It finds its applications mainly in organic synthesis for the preparation of Aryl iodides [Sandmeyer Reaction] from Aryl amine
Nutrition
The major uses of KI include use as a nutritional supplement in animal feeds and also the human diet. For the latter, it is the most common additive used to "iodize" table salt (a public health measure to prevent iodine deficiency in populations which get little seafood). The oxidation of iodide causes slow loss of iodine content from iodised salts that are exposed to excess air. The alkali metal iodide salt, over time and exposure to excess oxygen and carbon dioxide, slowly oxidizes to metal carbonate and elemental iodine, which then evaporates. Potassium iodate is used to add iodine to some salts so that the iodine is not lost by oxidation.
For reasons noted above, therapeutic drops of SSKI, or 130 mg tablets of KI as used for nuclear fission accidents, are not used as nutritional supplements, since an SSKI drop or nuclear-emergency tablet provides 300 to 700 times more iodine than the daily adult nutritional requirement. Dedicated nutritional iodide tablets containing 0.15 mg (150 microgram or mcg) of iodide, from KI or from various other sources (such as kelp extract) are marketed as supplements, but they are not to be confused with the much higher pharmaceutical dose preparations.
Pharmaceutical applications
Potassium iodide can be conveniently prepared as a saturated solution, abbreviated SSKI. This method of delivering potassium iodide does not require a method to weigh out the potassium iodide so it can be used in an emergency situation. KI crystals are simply added to water until no more KI will dissolve and instead sits at the bottom of the container. With pure water, the concentration of KI in the solution depends only on the temperature. Potassium iodide is highly soluble in water so SSKI is a concentrated source of KI. At 20 degrees Celsius the solubility of KI is 140-148 grams per 100 grams of water. Because the volumes of KI and water are approximately additive, the resulting SSKI solution will contain about 1.40 gram (1400 mg) KI per milliliter (mL) of solution. This is 100% weight/volume (note units of mass concentration) of KI (one gram KI per mL solution), which is possible because SSKI is significantly more dense than pure water—about 1.72 g/mL. Because KI is about 76.4% iodide by weight, SSKI contains about 764 mg iodide per mL. This concentration) of iodide allows the calculation of the iodide dose per drop, if one knows the number of drops per milliliter. For SSKI, a solution more viscous than water, there are assumed to be 15 drops per mL; the iodide dose is therefore approximately 51 mg per drop, assuming 15 drops/mL. It is conventionally rounded to 50 mg per drop.
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