How to Refill the Hg/HgO Reference Electrode (RREF0038)
Last Updated: 7/17/19 by Neil Spinner
1Hg/HgO Reference Electrode Components
The single junction mercury/mercury(II) oxide (Hg/HgO) reference electrode offered by Pine Research (part number RREF0038)
consists of several components (see Figures 1 and 2): a main body including a 14/20 PTFE adapter; a top cap; a threaded tip with embedded frit; and a protective bottle used to keep the frit wetted during shipping and/or short-term storage.
Figure 1. Single Junction Hg/HgO Reference Electrode (RREF0038) Components: (1) main electrode body with 14/20 PTFE adapter; (2) top cap; (3) threaded tip with embedded frit; and (4) protective bottle for shipping and short-term storage
Figure 2. Disassembled Single Junction Hg/HgO Reference Electrode (RREF0038) Components: (1) main electrode body with 14/20 PTFE adapter; (2) top cap; (3) threaded tip with embedded frit; and (4) protective bottle for shipping and short-term storage
2Refilling Hg/HgO Reference Electrode Fill Solution
Below, two possible methods for refilling the internal fill solution of the single junction Hg/HgO reference electrode are detailed. The first, Method A, may be a more intuitive and assumed technique to the user. However, Pine Research recommends the user perform Method B whenever possible, as this will be less likely to result in electrode failure.
Perhaps an obvious or intuitive method for refilling the solution inside the Hg/HgO reference electrode is illustrated in Method A (see Figure 3). First, the top cap can be removed from the main body. Next, the main body tube is drained of existing fill solution (if there is any) and rinsed with deionized water several times. A new 4.24M KOH (or a different electrolyte of the user's choice) is filled into the tube. Finally, the top cap is pressed back onto the main body.
Figure 3. Method A for Refilling Hg/HgO Reference Electrode (RREF0038)
This method, while intuitive, causes a higher chance for electrode failure due to an increase in internal pressure when pressing the top cap onto the body. Depending on the amount of liquid and air once the fill solution has been added, the trapped air may be compressed as the top cap is pressed and without adequate venting of this pressurized air, it is possible the leak rate may be greatly accelerated. Additionally, it is possible the frit may be ejected from the threaded tip if the pressure is not relieved. Therefore, it is not recommended that the user perform this method when refilling the electrode if at all possible.
Method B is the preferred and recommended manner of refilling the Hg/HgO reference electrode (see Figure 4). First, turn the electrode upside-down. Unscrew the threaded tip with embedded frit, and drain any remaining fill solution. Rinse several times with deionized water. Refill fresh 4.24M KOH (or another solution of the user's choice) into the electrode body, then screw on the threaded tip to the main body. Turn the electrode right side-up and store properly if not being used in an experiment.
Figure 4. Method B (Preferred) for Refilling Hg/HgO Reference Electrode (RREF0038)
By using the threaded tip as the piece that seals the electrode once refilled, there is less internal pressure increase and therefore likely a slower leak rate of electrolyte. There is also less chance of the frit becoming ejected due to internal pressure buildup, as described with Method A. One final suggestion for securing the electrode is to wrap a layer of parafilm around the lower portion of the top cap, onto the main body, to ensure a tight seal exists between the top cap and main electrode body.