The role of iron, one of the most common metals in the environment, is fundamental in many biological and geochemical processes, which determine its availability in the two main oxidation states Fe2+ and Fe3+. Its relevance in the environment, industrial applications, and human physiology, as well as in many other fields has constantly encouraged the development of analytical techniques for its accurate determination. Spectrophotometric methods are those most frequently applied for iron determination in real samples, with specific reagents for the two existing oxidation state right now. In the present work, two low-cost, non-toxic, colorimetric reagents are proposed: deferiprone and kojic acid. These compounds present peculiar features, in particular the formation of 1:3 complexes with Fe3+ of extremely high stability and absorptivity in a wide operative pH range. In this study, we show that both reagents can be used to measure the total iron content. Actually, the extremely low redox potential characterizing the FeL3 complexes permits to determine the total concentration of iron independently from the starting oxidation state, and assures the complete oxidation in presence of oxygen of any amount of Fe2+ to Fe3+ complexes. These features constitute a novelty in the analytical determination of total iron not requiring any pretreatment of the sample, contrary to the methods in use, devoted either to Fe3+ or to Fe2+, necessitating awkward and error generating oxidative or reductive processes. The analytical performance of the proposed spectrophotometric method has been evaluated for the full compliance with the Lambert-Beer law, the operative range of iron concentration, the influence of pH, and the interfering effects of other metal ions. Finally, it has been validated in terms of LoD, LoQ, linearity, precision, and trueness, and has been tested on total iron determination in natural water certified material and in two biological reference materials, human urine and serum.
