15.4.4 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).
15.4.4.1 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.
Check your REF regularly. If you do not see chloride salt crystals, or if you see air bubbles, your
REF needs maintenance.
15.4.4.2 Materials
• An over-saturated and thoroughly degassed KCl solution (700013253 )
• SB ref tool (700013145)—not included in the SenCell ship kit; should be purchased
separately
• Ordinary cotton wool
15.4.4.3 Procedure
Follow the procedure to perform maintenance on Salt Bridge Reference.
Note:
Use proper eye and skin protection when working with solvents.
December 16, 2021, 715007395 Ver. 00
Page 144
