pH Electrode Maintenance

How do I maintain, store, and restore my PASCO pH electrodes?

Cleaning

  • 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 dilute solution of chlorine bleach.

Storage

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 microorganisms 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. Store probe dry.

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

Restoration Procedure: Electrode is unresponsive

If the electrode is not responding quickly:

  1. Soak the electrode in 12 Molar NaOH (sodium hydroxide) for one minute. Rinse completely.
  2. Soak the electrode in 1 Molar HCl(hydrogen chloride) for one minute. Rinse completely.
  3. Soak the electrode in 0.1 Molar Hydrochloric Acid (HCl) for 15 minutes. Rinse completely.
  4. Soak the electrode in a pH 7 buffer solution for 30 minutes. Rinse.
  5. Try to calibrate the sensor to pH 4 and pH 10. If the electrode will not calibrate or hold the calibration, it should be replaced (PS-2573 pH Electrode)

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