Managing Electrolysis in Electrophoresis Experiments

Electrophoresis ExperimentWhen an electric current flows through a solution containing a buffer, electrolysis reactions may occur at the electrodes if the voltage drop at the electrode is greater than the EMF required for the reaction. For the electrolysis of water into hydrogen and oxygen, this voltage is about 1.2V. At the cathode, electrons combine with hydrogen ions to produce hydrogen gas, and at the anode, electrons are removed from oxygen ions to produce oxygen gas. The purpose of this paper is to understand the conditions that can lead to bubble formation when running electrophoresis experiments, assuming that the voltage drop at the electrode exceeds the threshold EMF for electrolysis.

As expected, temperature, pressure, and current flow are the major factors in determining whether or not bubbles form. One point of interest is the large effect of solubility on bubble formation: hydrogen bubbles do not readily dissolve in aqueous buffer, and since twice as much hydrogen as oxygen is created during the electrolysis of water, hydrogen bubbles are more likely to form. Several methods can be used to mitigate the effect of bubbles on an electrophoresis experiment:

  • Bubble formation can be reduced by reducing buffer conductivity, since this will reduce total current without affecting the electric field gradient. Increasing the electrode separation or decreasing the channel cross sectional area will also reduce the overall current flow.
  • If the hydrogen-producing cathode is located downstream of the microchannel, the likelihood of bubbles interfering is reduced, since only oxygen bubbles (which have a higher solubility) will be flowing in the channel.
  • If packing is used in the microchannel, higher pressures are more likely to be involved, so that oxygen bubbles may stay dissolved in the buffer.
  • Depending on the total current and total run time of the experiment, the volume of bubbles generated may not interfere significantly with the experiment.
  • Separation of the electrode from the fluid stream, as is typically done in capillary electrophoresis by placing the electrodes in the buffer reservoirs, will obviously prevent electrolysis gases from entering the fluid flow, although this may not always be feasible. 

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