before has been react with ligand, why ferum must be in Fe(II) condition?

Question

i want to determine iron in water sample using UV spectroscopy. but iron in the sample must be in Fe(II) condition before react with ligand or 1,10-fenantrolin.why it is so?why the intensity of the complex formed is depend on the pH of the solution?

Answer 1

Fe2+ and Fe3+ form completely different complexes, of different colours and so on. I aslo assume that the ligand you are using is an acid, which is why its concentration depends on the pH.