For most applications, hot water with domestic cleaning detergent can be used for cleaning.
For lime and other hydroxide containing solutions, clean with a 5-10% solution of hydrochloric acid.
For solutions containing organic fouling agents (fats, oils, etc.), clean probe with limonene or acetone.
For algae and bacteria containing solutions, clean probe with a chlorine bleach containing liquid.
Short-term: If you expect to use the probe again within ten days, clean and immerse the pH electrode in the soaker bottle filled with pH 4 buffer solution that contains 1 g of potassium chloride (KCl) per 100 mL of solution. Alternatively, pH electrode storage solution can be purchased as pH storage solution SC-3507. (Storing the electrode in distilled water will decrease the life of the electrode.)
If you soak the electrode for more than ten days, then you run the risk of microrganisms contaminating the buffer solution unless you either use a buffer preservative or follow the long-term storage recommendation below:
Long-term: Clean and dry the probe. One to two days before you wish to use it again, restore the probe by soaking it alternately into 0.1 M HCl and 0.1 M NaOH solutions for two minutes each. Repeat once. Following that, soak in a pH 4.0 buffer solution until use. If this restoring procedure fails to improve the responsiveness of the electrode, it should be replaced.
Removing Air Bubbles
Unstable readings may be caused by air bubbles attached to the inner electrode of the probe. To remove these bubbles, hold the electrode firmly by the handle and swing it quickly in an arc several times. If you still cannot eliminate the air bubbles, heat the electrode to 50-60 Celsius in tap water. Grab the electrode with an insulating glove or towel and shake it vigorously again.
See Tech Note 630.
Warranty/ Expected Life
The pH electrode's that PASCO carries are covered by a 1 year manufacturer warranty. The pH sensor should be replaced when it becomes unresponsive even after proper cleaning and restoration. pH sensor life is 1-5 years in a typical educational environment. To obtain several years of life from the probe, the probe must be stored properly and used infrequently.