October 27, 2015 aci Our Products Ferric Ammonium Citrate Chemical formula :C6H5+4yFexNyO7 CAS No. : 1185-57-5 Description : Ammonium ferric citrate is a food additive with E number E381 used as an acidity regulator.[citation needed] It is a green or reddish-brown powder which is very soluble in water.