Ammonium iron (III) citrate solution, 12.5 %, sterile, ready-to-use, 20 mlAmmonium iron (III) citrate solution, 12. 5 %, sterile, ready to use, Density (D) 1,06 g cm, Boiling point (bp) 100 C, Storage temp. +15 to +25 C Sterile Directions for use Ammonium iron (III) citrate (ferric ammonium (III) citrate) is used as additive in nutrient media for detection of Listeria species. Hydrolysis of esculin by Listeria species results in 6,7 dihydroxycoumarin which reacts with ferric ions producing blackening of the medium.