Gamry sells the Saturated Calomel Reference Electrode and Silver-Silver Chloride Reference Electrode. Proper reference electrode care must be taken to ensure continued accurate measurements. The tip of the reference electrode is porous glass frit or electro porous KT glass (opaque white). The frit allows ionic transport into the electrode. In order to operate properly the frit must always be kept wet with electrolyte.
Both reference electrodes are filled with Saturated KCl. To fill the reference electrode, slide the rubber grommet located at the top of the electrode down. This will reveal a small filling port where saturated KCl can be added.
Both Ag/AgCl and SCE reference electrodes should be stored in just slightly less than saturated KCl solution. Keeping the solution just below saturation allows enough ionic flow to prevent salt crystals from forming in the glass pores. The frit must be kept wet at all times to ensure the impedance of the electrode remains low.
Checking the Impedance of the Reference Electrode
It's very important for optimum potentiostat performance that the impedance of the Reference Electrode in your cell is low! A high impedance Reference Electrode will cause problems that range from simple overloads to potentiostat oscillation.
The impedance of your Reference Electrode should be less than 1 kohm. Impedance higher than 1 kohm is not good and impedance higher than 5 kohm is unacceptable and must be corrected.
- Partially fill a beaker with electrolyte. If you normally use a Luggin capillary, the concentration of this electrolyte should be approximately the same as that of your test solution.
- Immerse the tip of your Reference Electrode into the solution. If you will be using a Luggin capillary, place the tip of the Luggin capillary in the solution and place your reference in the Luggin. Make sure you have an unbroken electrolyte path from the tip of the Reference to the tip of the Luggin capillary.
- Add a high surface area platinum wire or graphite rod counter electrode to the solution.
- Connect the Reference Electrode to the Working (green) and Working Sense (blue) leads of your potentiostat. Connect the graphite rod to the Reference (white) and Counter (red) electrode leads
- Open Gamry Framework and go to Experiment>Utilities>Measure Reference Electrode Impedance.Framework will now run an EIS curve measuring the impedance of the reference electrode. Once it is finished it will tell you if the impedance is acceptable, and also gives you the measured impedance and phase angle of your electrode.
- If the program tells you the impedance is acceptable then you may continue with your experiments. If the impedance is out of range, one possible solution is to replace the frit. Please see the following section for details on this section.
Replacing a Reference Electrode Frit
A porous glass frit should be replaced if the impedance of the reference electrode is out of specification (see above), or if it has been allowed to dry out, has been cracked or chipped, or if it has become discolored. A frit cannot be reused. You will need a new porous glass frit and a piece of shrink-wrap PTFE tubing before beginning this process.
- Remove the old frit by cutting the heat-shrink PTFE. A sharp knife or razor blade is ideal
- Place a single porous glass frit inside the piece of heat-shrink PTFE tubing supplied. See below
- Slide the PTFE over the end of the reference electrode and be sure that the porous glass frittouches the end of the glass tube. Warm the PTFE with an electric "heat gun" until the PTFE shrinks tightly around the porous glass fritand the end of the reference electrode. Do not hold the heat gun too close or the PTFE will melt. Rotate the reference electrode to evenly heat all sides of the PTFE. A suitable heat gun can be purchased from your local laboratory supply house. A common "paint stripper" heat gun can also be obtained locally. See below.
- Trim the excess PTFE so that it is even with the end of the porous glass frit. If you do not, the excess PTFE tube can trap a gas bubble and isolate your reference electrode from the solution.
- Refill the interior electrode body with saturated KCl. Allow the electrode to soak in saturated KCl for at least 1 hour before use to ensure the new frit is completely wet.
- Finially, measure the impedance of the reference electrode to make sure the frit replacement and re-wetting process worked correctly. See the above section for details on this.