OLD IRONIC FACT WORTH KNOWING
Many of us use commercial ferric ammonium citrate (FAC) as a soluble source of iron(III) for biological experiments. The commercial product appears often in different colors, primarily brown or dark green or mixtures of both.
What is in the bottle?
What is in the solution?
In an “old” article published in 2015 in Eur J Inorg Chem. 4159-4162 Tenne-et-al. described a trinuclear ferric citrate complex as major component of both brown and green FAC but the green product contained also a substantial (often equal) amount of dinuclear ferric citrate complex.
When applying FAC in biological studies and seeking reproducibility within and across laboratories, we should be aware of the above facts about FAC. Similar considerations should be used when using commercial Ferric-citrate or fresh salt prepared with citric acid and inorganic-iron salts. In nature, the chemically relevant forms of iron might differ from those often prepared in laboratories for biological experimentation. Therefore, in publications using FAC, it is recommended that the Methods section include the CAS Reg. No. for the exact FAC compound used.