pH Cleaning

The following procedure applies specifically to the IJ44 pH electrode. The solutions and procedures can also be adapted for cleaning other styles of pH electrodes.

pH Cleaning

1. Clean the electrode periodically dependent on the application. Remove the sleeve as in Preparation. Clean the membrane, ground glass stem and sleeve with solvents, detergents, or acid. DO NOT USE ABRASIVE MATERIALS!

Alkaline samples and scale - Soak the electrode in 6M HCl, 3M sulphuric, or chromosulphuric acid for 15 minutes. Wash well with tap water and soak before use.
Biological and protein samples - Soak the electrode in 0.1% pepsin / 0.1M HCl for 1 hour or overnight. Rinse the electrode and then soak in pH7 buffer which contains 0.5g KCl /100mL before use.
Grease and oil - Wipe the membrane and ground stem with cotton or tissue soaked in acetone or methylated spirits. Wash with deionised water and soak before use.
Dirt and organics - Wipe the tip with cotton or tissue soaked in a mild non-alkaline detergent (e.g. Palmolive). Wash with deionised water and soak before use.

2. Rejuvenation of the response of aged pH electrodes may be obtained by immersing for 10 seconds (no longer) in 10% hydrofluoric acid and immediately washing well in tap water. This treatment should be used sparingly.

pH Maintenance

When not in use, it is preferable to keep the electrode immersed in 2M KCl. If this is not available, pH 4 or 7 buffer is acceptable. This keeps the reference from drying out and the pH glass hydrated, so the electrode is ready for use immediately.
How often does the electrolyte need replacing? This depends on the sample being measured, and is best determined by experience. Error can be determined by comparing readings before and after renewal of the electrolyte on the same sample. Normally, errors of less than a few hundredths of a pH can be expected after a full day's use and electrolyte need only require weekly replacement.
For long term storage, remove and clean the sleeve. Replace the sleeve without electrolyte and attach the wetting cap, filled with deionised water. Note: After long term storage algae or mold growth may occur inside the wetting cap. This can be removed by soaking in dilute chlorine (bleach) solution.

pH Helpful Hints

For greatest accuracy in pH measurement, follow these guidelines:

Use the same technique to measure samples which was used for calibration. Be consistent with stirring rates, times and conditions.
Calibrate with buffers which are close in temperature to that of the sample.
Calibrate the pH electrode regularly, e.g. once an hour for accuracy to within 0.01 pH, or once a day for accuracy to within 0.1pH.
Use fresh buffers for calibration. Avoid contamination of the stock buffer solution and do not use beyond the expiry date.
Use a dedicated pH meter. DO NOT USE A MULTIMETER!
Keep all connections dry.
Immerse the electrode far enough into the solution to insure the reference junction (where the ground glass stem contacts the end of the sleeve) is below the surface.
Allow adequate time for the electrode to stabilize in standards and samples before taking a reading. Clean the electrode periodically. Allow more time for aged electrodes.
Do not use the pH electrode in solutions of fluoride ion at low pH. This will etch the glass membrane.
Sulphide vapors can permeate the electrode wick and contaminate the reference element. Minimize contact in such environments and change the reference electrolyte frequently.
This electrode is suitable for use in TRIS buffers, as the external reference electrolyte does not contain silver ions which cause fouling.