pH probes/testers

[franco]

Hi everyone,

I’ve just bought a class set + spares (15) of the pH probe/tester from Wiltronics (top of page 36, 2009 catalogue).
I’m finding calibrating for the first time to be a very long-winded affair which may take hours to complete. The instructions are easy to follow and require the probe to be calibrated at 2 points: 6.86 and 4.01. Finally, the probe should be re-immersed in the 6.86 buffer. If the last reading isn’t 6.86, the whole procedure should be repeated. Rinsing with distilled water and wiping off with a tissue between each rinse and each immersion in buffer is proving to be very time consuming.
Needless to say, of the 5 I’ve done so far, all required a repeat of the calibrating procedure and one will not calibrate at all.
If they’re unused for a long time (how long is long?) or the batteries die, they need to be calibrated again, so I figured that as I don’t need them until next year I’d store them without the batteries.

Has anyone else bought these probes? Am I being too fussy with accuracy and rinsing/wiping off? I don’t have much recent experience with pH probes/meters and would appreciate any input from you guys.

Regards,
Fran

[Robb]

Hi Fran,

The common hole to fall into is calibration of the pH probes and in my career I have done countless calibrations and even pH electrode re-juevinations.

One question....

How well do you know the concentration of the pH 4.01 solution and what compound is it. (This matters quite a lot).

The thing to remember is when the pH 6.86 is used after the pH 4.01 solution you need to further use a pH 9.00 solution as well.

In fact when you calibrate the electrode what you are actually doing is a graphical representation..... I will try to explain...

Using the pH 4 solution will give the electrode a gradient to use and when you calibrate with pH 6 and 9 solutions you infact include the slope of the graph. When you use 3 solutions you will find that the acuracy will change considerably...

Try this, and it will get you out of a load of trouble. Calibration should only take no more than 5 mins. (as a guide). Don't be fanatical about this..

Also some food for thought, pH is only a change in electrode voltage so this will never be constant over temprature as well.

Cheers,

Robb.....

[Robb]

Hi all, Fran....

One more thing you can re-juevenate a DEAD pH PROBE by a procedure that I have listed many years ago on this forum. If you search for it you will find it, it saves a lot of grief and will have the non-responsive pH electrodes working in no time.

Rinsing with distilled Water is the only thing I would recommend to be done with copious amounts of water. (Becareful of the Dist. Water pH as well).

Cheers,

Robb.....

[KarenN]

Hi Robb,
just wondering if you can repost / point me in the right direction to find your "re-juvenation method" for a dead pH probe.
I have searched the forum but cannot find your old posting.

Many thanks, Karen

[Lyn]

Karen,
Just search for - pH electrode rejuvenation technique - in the Chemistry and Labware - general forum. There is some general info posted Sep 11 2006 but doesn't state the solution (pH7) used or the pH Soaking Solution used for storage of electrodes. There is also a post dated Dec 7 2007 where you can request info for recipes for rejuvenation by going through the private message option. Robb also explains why his recipes are not posted for general consumption on the Chemtalk website.
Lyn.

[KarenN]

Hi Lyn,
found the information, thanks very much.
Karen