Internal filling solutions for refillable HORIBA reference and combination pH electrodes. These are the electrolyte that fills the reference chamber and completes the electrical circuit through the liquid junction — without it at the correct level and concentration, the electrode cannot produce a stable reading regardless of how well the glass membrane is working.

Refillable electrodes are topped up as part of routine maintenance. The level falls through normal outflow at the junction, and the solution should also be replaced periodically because it gradually becomes contaminated by sample carried back through the junction. A slow, drifting or noisy pH reading on a refillable electrode is very often nothing more than low or stale filling solution.

What is available

• 310 (part no. 3200043622) — internal filling solution.
• 300 (part no. 3200043640) — reference electrode internal solution for pH electrodes, 250 mL.

Good practice

• Keep the filling solution level above the sample level so flow is always outward through the junction — this prevents sample being drawn into the reference chamber
• Open the filling port during measurement and close it for storage
• Replace, rather than just top up, the solution if readings remain unstable after cleaning
• Never substitute deionized water for filling solution — it destroys the reference potential
• Match the solution to the electrode type; using the wrong concentration shifts the reading

Applications

• Routine maintenance of refillable glass-body pH and reference electrodes
• Restoring stability to an electrode with slow or drifting response
• Recommissioning an electrode that has been in storage
• Laboratory and field pH programs running refillable rather than gel-filled electrodes

Related items

Reference electrodes, refillable combination pH electrodes, electrode cleaning reagents, pH buffers and KCl caps are all stocked — see the Horiba Parts & Accessories collection. The 330 gel-type 3.33 mol/L KCl reference solution is listed with the U-50 Series accessories, and ion-selective electrode filling solutions are listed separately.

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