Fischer Scientific AB15 -- Unable to calibrate or take any readings.
The electrode you have is a combination electrode with an integral calomel reference half-cell and built-in temperature probe. Since the temperature reading is good, the temperature probe is okay. It isn't part of the pH circuits anyway. (Your meter uses the temperature to calculate a temperature correction of pH.) Something else is going on with the electrode proper. Its funny behavior suggests to me that it has dried out internally.
pH electrodes don't last forever. How old is this one? If it's an old one, it's probably time to replace it. If it's new and doesn't work, it may be under warranty.
If you shop for a new electrode, get a gel-filled one. And go for one with a silver/silver chloride reference instead of a mercury one -- especially if you are using it on food or other samples that may be consumed. Another consideration about calomel electrodes: they take hours to recover from relatively small temperature changes. Ag/AgCl references aren't as sluggish.
Finally, take care when storing the electrode. It should be stored under humid conditions to keep it from drying out. The best way is to put a small piece of cotton or glass wool soaked with distilled or deionized water inside the plastic end cap. For shorter-term storage, e.g., overnight, you could immerse the tip in pH 7 buffer.
Fisher Science &...
on Nov 22, 2017