Unveiling iron chemical speciation in low sample volumes by a spectroelectrochemical approach

Spectroelectrochemistry (SEC) in the UV-vis region has shown interesting possibilities for analytical purposes, especially by means of chronoamperometric (CA) measurements in normal reflection mode using screen-printed carbon electrodes (SPCE). In this work, a study of the electrochemical and optical response of mixtures with different proportion of Fe(II)- and Fe(III)-ions complexed with ortho-phenanthroline (OP) was conducted by taking advantage of the appearance/disappearance of the intense red color of Fe(II)-OP complex as Fe(III) is reduced and Fe(II) is oxidized, respectively. As a proof of concept, the calibration curves obtained for mixtures under reduction (-0.2 V) and oxidation (+1.0 V) conditions were used to quantify the amount of Fe(II) and Fe(III) in a real sample. The analysis showed that the SEC-based strategy is a suitable tool for iron speciation using a reduced volume of sample.