Sensitivity electrode of refillable pH meter

Instead of adding KCl solution to my refillable pH meter, like mentioned in the booklet that came with it, I exchange all of the old fluid for new KCl solution. Afterwards the electrode seems more sensitive and it gives a more stable reading.
I have never experienced an actual lowered level of KCl solution in the probe every time I check, so according to the booklet I don't even have to add solution. (I always keep the electrode submerged in storage solution and refresh it afer every reading btw.)

Question 1:
Can anyone explain the reason why the electrode seems to function even better this way than it already did?

Question 2:
I've read several meter instructions from different brands, and here and there I read the use of methanol or IPA for cleaning certain substances.
Wouldn't this damage the membrane around the electrode? 
(I only clean with a highly diluted dish soap solution and rinse it with distilled water, for the rest I only rinse with distilled water, nothing else).


  • @Doreen, in our lab we used to replace the solution whenever a refill was needed, we used lots of electrodes and at different temps and aqueous solvents so we went through a lot of filling solution (and electrodes, btw). 

    You will always have some 'grime' generated at the electrode. Some of it comes from the KCl, some might come from the DI water or mQ water used to prepare the solution (DI water and even mQ water still contain breakdown products of the resins used, they just do not conduce electricity). Over time those might adsorb at the Ag wire. 
    Another possibility is that since the electrode is not one of the sealed ones, evaporation and seepage through the junction changes the concentration of KCl. The usual 3M KCl is only below the saturation line at room temp. Over time you might have precipitation of KCl, which might happen at the bottom, or at the Ag wire. This creates a coating that delays the response of the electrode. 
    Replacing the solution brings down the concentration of KCl, so that whatever was precipitated redissolves.

    The cleaning question. Methanol and IPA are good to remove organics that might deposit at the electrode. Glass stored in mildly acidic environment becomes a titch more lipophilic than glass stored neutral or alkaline. Organic matter for sure will deposit by adsorption or creating a film. You won't ruin the electrode, just do not leave them in contact for a long time. If you have a squeeze bottle it's easier, as you can just rinse the bulb, then use DI water to re-wet the junction as quickly as possible, then place into the storage solution. We do that all the time when we work in aqueous solvents. The glass membrane might become contaminated with the most disparate stuff, proteins seem to like it a lot (in these cases you would soak the electrode in 0.5 M HCl, or digestive enzymes at pH 2-3), heavy metals can be removed with a 1M HNO3 solution. Even electrodes that are deemed bad can sometimes be reconditioned with some care. 

  • @lmosca
    Thank you so much for your answers! :+1:
  • Hello. Speaking of ph meter, I found one of our electrodes' bottle dry. So I soaked it in KCl solution but it didn't give the right measuring. Any thoughts? :/ 
  • edited February 17
    You mean that the electrode itself has dried out? I don't know for how long, but given the fact that it didn't measure right, it seems it's beyond 'repair'.

    At work we have the same problem, some people seem to fail to see the importance of placing the electrode back into the storage solution, so every once in a while there's a dried out electrode that needs replacing.
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