Old PH probes

[fio1022]

Is there a way to rejuvenate old PH probes that will no longer calibrate?
Just wondering before I throw them out.

[Randy Holmes-Farley]

Try soaking it in acid overnight. Straight vinegar or 1:10 diluted muriatic acid in water. Then try calibrating again. :)

[fio1022]

If that will work is it just a temporary fix?
What make a probe go bad?I can still see fluid inside it.

[JD52]

This is an excellent question, hoping for more replies...

[Randy Holmes-Farley]

The acid cleaning is a permanent fix if it works. It removes junk that is coating the glass bulb. I discuss cleaning here:

Measuring pH with a Meter
http://www.advancedaquarist.com/issues/feb2004/chem.htm

About the only other thing to do is empty and refill it if it is not a sealed electrode (not usual for hobby probes). Any number of other things can go wrong, including broken internal wires and parts. :)

[loudell]

The reason that a pH or ORP probe (which has a similar construction) wears out is due to the internal electrolyte fluid/gel. This gel has a small amount of minute communication with your water sample and over the course of months and years the gel will dilute. This also can account for some drift necessitating the need for recalibration. Look at the viscosity of the gel in a new probe versus the gel in an old probe. Unfortunately no amount of cleaning will chemically replace the missing electrolyte inside the probe. In theory the gel can be replaced but my experience is that it will not perform as well as a new sealed probe.
To get good life from your pH probe you should select one that has a large internal electrolyte gel fill (longer length probe) and place it in an area of slower flow.

[Randy Holmes-Farley]

Did you try soaking it yet?

[fio1022]

I soaked two probes overnight.The first probe,the bulb broke.The second almost was able to calibrate,fell just short.
I'm going to soak it for a few day to see what happens.
I don't plan to use probe ,only as an emergency back up if needed.

[Randy Holmes-Farley]

OK, sounds good. :)

[Boomer]

Once you have done what Randy has suggested, rinse it and then soak it in methyl alcohol for few min, rinse it and then soak in 3M KCl (pH Buffer 4) for 1-2 hr before you re-cal it. These are old tricks to rejuvenate pH probes. If it does not recal correctly they it belongs is the circular file :)