Ammonium ferric citrate
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Ammonium ferric citrate is a food additive with E number E381 used as an acidity regulator. It is a green or reddish-brown powder which is very soluble in water.
The molecular formula of ammonium iron(III) citrate is variable. It can be prepared by adding Fe(OH)3 to an aqueous solution of citric acid and ammonia. The brown form is approximately 9% NH3, 16.5–18.5% Fe, and 65% hydrated citric acid; the green form is approximately 7.5% NH3, 14.5–16% Fe, and 75% hydrated citric acid. The green type is more readily reduced by light than the brown.
Other uses for ammonium ferric citrate include water purification and printing (cyanotype). It is used as a reducing agent of metal salts of low activity like gold and silver and is also in a commonly used recipe with potassium ferricyanide to make cyanotype prints. Ammonium ferric citrate is also used in Kligler iron deeps to determine hydrogen sulfide production in microbial metabolism.
Ammonium ferric citrate is present in Scottish carbonated soft drink Irn-Bru.
In medicine, ammonium ferric citrate is used as a contrast medium. It is also used as a hematinic.
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- ↑ U.S. Patent 2,644,828
- ↑ 2.0 2.1 Template:Merck13th
- ↑ IRN BRU: our drinks, nutritional information
- ↑ Therapeutic Goods Administration. "Chemical Substances" (PDF). Archived (PDF) from the original on 8 July 2009. Retrieved 27 July 2009.
- ↑ The United States Pharmacopeial Convention. "Revisions to FCC Sixth Edition 2S". Retrieved 27 July 2009.
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- Ammonium compounds
- Iron compounds
- MRI contrast agents
- Photographic chemicals