Considerations on the use of spectroelectrochemistry in reflection mode for quantitative analysis: Study of the Fe(III)/Fe(II) - orthophenanthroline system

Theoretical and experimental considerations are made about possible analytical applications of spectroelectrochemistry (SEC) in reflection mode using screen-printed electrodes. The system Fe(III)/Fe(II) - orthophenanthroline is taken as a model of electrochemical generation and consumption of a substance that is strongly absorbing: the Fe(II) - orthophenanthroline complex. Different possibilities of quantification are discussed, including cathodic and anodic peaks in cyclic voltammetry and both electrochemical and optical signals acquired in chronoamperometric experiments. Among these, the evolution of absorbance with the square root of time at a constant potential has shown interesting possibilities for the determination of Fe(III)-ion at micromolar level (LOD = 2 10-6 mol L-1). Moreover, this method appears to be resistant to the presence of other electroactive species such as Cu(II)-ions.