Abstract
A microfluidic platform for hydrodynamic electrochemical analysis was developed, consisting of a poly(methyl methacrylate) chip and three removable electrodes, each housed in 1/16” OD polyether ether ketone tube which can be removed independently for polishing or replacement. The working electrode was a 100-μm diameter Pt microdisk, located flush with the upper face of a 150 μm × 20 μm × 3 cm microchannel, smaller than previously reported for these types of removable electrodes. A commercial leak-less reference electrode was utilized, and a coiled platinum wire was the counter electrode. The platform was evaluated electrochemically by oxidizing a potassium ferrocyanide solution at the working electrode, and a typical limiting current behavior was observed after running linear sweep voltammetry and chronoamperometry, with flow rates 1−6 μL/min. While microdisk channel electrodes have been simulated before using a finite difference method in an ideal 3D geometry, here we predict the limiting current using finite elements in COMSOL Multiphysics 5.3a, which allowed us to easily explore variations in the microchannel geometry that have not previously been considered in the literature. Experimental and simulated currents showed the same trend but differed by 41% in simulations of the ideal geometry, which improved when channel and electrode imperfections were included.
Highlights
We introduced geometrical imperfections in the model based on channel profilometry and on scanning electron microscopy (SEM) on the electrode tip, obtaining predicted currents that are closer to the experimental data
The results of hydrodynamic LSV runs performed at different flow rates are shown in Figure 4, where ferrocyanide was oxidized at the working electrode (WE)
While the discrepancy between simulation and experiment might be due to any number of deviations from the idealized model, we considered imperfections that we were able to measure or have some evidence of: 1 a geometrical variation in the channel shape, and 2 that the electrode was not flush with end of the polyether ether ketone (PEEK) housing but was instead recessed in the lumen of the PEEK tube
Summary
In the first experiment we will determine if typical LSV values for hydrodynamic microelectrodes are obtained using this platform and the potential at which the amperometry should be run to ensure limiting currents at each flow rate for comparison with the numerical simulation.
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