Spectrophotometric Determination of Iron(II) with 5-Nitro-6-amino-1,10-phenanthroline

Gravimetric, titrimetric, polarographic, optical and radiochemical methods have been reported for the determination of iron(II) and (III). Numerous reagents have also been reported for the spectrophotometric determination of Fe(II); for example, thiocyanate, dipyridine, tripyridine and 1,10-phenanthroline. The 1,10phenanthroline family has been extended to the use of dihydroxy, dimethyl, nitro and diphenyl derivatives. The spectrophotometric determination method of a red-orange complex that forms between iron(II) and 1,10-phenanthroline is practical and sensitive. An excess of reducing reagent, such as hydroxylamine or hydroquinone, is needed for iron(III)1−7. In the transition series elements zinc(II), copper(I) and copper(II) would be expected to form labile outer orbital complexes with 1,10-phenanthroline since all their 3d are already occupied. Quantitative observations confirm that their rates of reaction with 1,10-phenanthroline are faster than iron(II) (ferroin forms). Nickel(II), however, despite the presence of eight electrons in the 3d orbitals, reacts slowly with 1,10-phenanthroline and mon-, bis and tris-1,10-phenanthroline complexes of nickel(II) have been reported. The manganese complex is much weaker than the iron(II) complex. This paper describes a simple and accurate visible spectrophotometric method and optimum conditions for the direct determination of iron(II). The method is based on a complex formation between iron(II) and