Ferrozine-A New Spectrophotometric Reagent for Iron

-N=C&N-, have been known to react as bidentate ligands with certain metal ions such as ferrous, cuprous, and cobaltous, to give colored complex species (1-6). This effect was first noticed with the ferrous ion ( I ) , and since this complex of a given compound is generally of a more intense color than are those with other ions (7), the atomic configuration in question was given the trivial name of the ferroin group. During the last century, hundreds of compounds containing the ferroin group have been synthesized (7), the majority of which demonstrate the ability to form complexes with the ferrous ion. Most of these complexes are only weakly colored, are unstable under normal physical conditions, or are formed over a very narrow pH range. A few of these compounds, however, form stable, intensely colored species with the ferrous ion and are, therefore, suitable for the quantitative determination of iron (8). Examples of compounds which have found acceptance for such use are 1,lOphenanthroline (9), 4,7-diphenyl-l,lO-phenanthroline (IO), 2,2‘-bipyridine (I]), 2,6-bis(2-pyridyl)-pyridine (11). 2,4,6tris(2-pyridyl)-1,3,5-triazine (12), and phenyl 2-pyridyl ketoxime (13, 14). Many of these reagents are the product of difficult and tedious organic syntheses and, hence, are high in cost (14). Although for even the most expensive of these reagents, the cost of a single manual analysis is fairly low, when one considers automated continuous instrumental analysis, a lowcost yet highly sensitive reagent would be desirable, since the cost of maintaining such an analytical instrument with I