16.4.2.1 Polishing
Polishing the reference electrode is done using the factory-supplied polishing kit, which contains
diamond slurry and a polishing disc.
To initiate polishing:
1. Shake the diamond slurry thoroughly before use.
2. Rinse the polishing disc with demi-water before applying the diamond slurry.
3. Apply a few drops of slurry to the wetted polishing disc, and polish the electrode with a
figure-8 motion for about one minute. Apply only gentle pressure.
4. Clean the electrode with an ethanol-wetted tissue and inspect the surface visually. Repeat
the procedure if necessary, until the shining metal REF surface appears.
5. Clean the polishing disc with demi-water.
6. Store the polishing disc in its plastic bag.
16.4.3 Ag/AgCl salt bridge
Three aspects determine the proper function of an Ag/AgCl reference electrode.
• The chloride concentration must be kept at a strictly fixed level. This is best guaranteed by
using a saturated chloride salt solution at a constant temperature.
• The salt bridge must allow proper electrical contact with the mobile phase. The higher the
leakage through the frit, the better the conduction.
• Air bubbles inside or close to the salt bridge will lead to instability of the three-electrode
configuration. Because of their extreme compressibility, changes in conductivity and the ionic
equilibrium of the REF occur. This increases the noise considerably.
The REF is factory-filled with KCl unless specified otherwise. Other chloride salts should be used
when the mobile phase contains perchlorate (use NaCl) or a high percentage of organic modifier
(use LiCl).
16.4.3.1 Saturation and air bubbles
After prolonged use, the salt bridge in the REF will no longer be saturated, which usually leads to
poor reproducibility in electrochemical detection. The potential of the REF is determined by the
chloride concentration. If the salt bridge is not saturated and the KCl concentration changes:
• The noise in the system will slowly but continuously increase.
• The background current will increase.
• Sensitivity to movements and pump noise will increase.
If an air bubble is trapped in the salt bridge or in the cotton plug that separates the salt bridge and
the mobile phase, the flow cell becomes extremely sensitive to flow fluctuations and vibrations.
This is caused by the high compressibility of the trapped air. Inspect your REF regularly. If you do
not see chloride salt crystals, or if you see air bubbles, your REF needs maintenance.
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