Cobalt ferrite magnetic nanoparticles as stirring actuators to improve UV-Vis spectroelectrochemical measurements in normal reflection mode.

Spectroelectrochemical (SEC) measurements using UV-Vis radiation in normal reflection mode (or normal configuration) are less sensitive than parallel approaches, since the volume of sample monitored has a much lower proportion of the diffusion layer created by the electrochemical processes, i.e., the region where relevant optical changes take place. In contrast, the normal configuration is more robust and reproducible and, as of today, is the only commercially available. This work presents a strategy to enhance normal reflection SEC measurements of Fe(III)/(II)-orthophenanthroline system using a screen-printed carbon electrode (SPCE), improving competitiveness with parallel designs. This method required the design of a new measuring cell based on the geometry of the commercial one, but replacing the eight magnets by a non-magnetic closing system. The developed approach involves adding cobalt ferrite magnetic nanoparticles (CoFe₂O₄ MNPs) to the analyte solution and coupling the SEC cell to a conventional magnetic stirrer. The resulting nanostirring, driven by MNPs movement, enhances mass transport toward the electrode. This accelerates diffusion layer renewal, leading to a noticeable increase of both electrochemical and optical signals.