how to check if ph probe is bad

[rockytoptim]

I did a search last week here on HBT and of course I didn't bookmark it and now I can't find it. I have a ph probe that ia 1.5 years old and I thought I read that you could use ammonium to check if the probe is still good or not. Whats the ph of ammonium supposed to be or is the probe still good as long as its calibrates to 4.01 & 7 buffers. Mine is a manual cal not automatic.

Thanks in advance.

 

[Brad2287]

I would check on the specifics for your make and model but here is the quality criteria I use on my ROSS Orion probe.
First turn the meter to read mV
Measure the pH four buffer.
It should be between 150 and 210 mV
Measure the pH seven buffer.
It should be between -30 and 30 mV.
The absolute difference between the four and seven buffer should be between 160 and 180 mV.
If I notice that the electrode is drifting unusually or the response is slower I also take this as signs of electrode degradation.
If the electrode fails this qc criteria it is cleaned and refilled per the manufacturers specs then retested. This tends to help but will not fix a worn out or mistreated electrode. I am guessing your electrode is not refillable so that part most likely does not apply.