pH probe evaluation and testing.

[karimwassef]

I calibrate my pH probes every month almost. The result are in line with what I expect, but I want to get better.

So I'd like to have a separate and very accurate method to confirm my pH down to two digits: 8.26 vs. 8.25 for example.

This isn't to use continuously. It's to spot check my probes' performance over time.

It can be a titration test, but I'm terrible with colors (don't think I can get to the accuracy I need that way anyway).

So- how can I get close to what I want without spending over $300?

[bertoni]

What probe are you using? If you want very high accuracy, you likely will need to calibrate more frequently. The one-shot calibration pouches probably will be more accurate than the bottles in this application. Getting ±0.01 is a tough goal.

[karimwassef]

I'm using Apex scientific grade pH probe (the more expensive one).

I do use the single use calibration pouches now.

So, how do I independently measure my pH accurately?

[Dan_P]

Here is a thesis that might assist in answering your question. The discussion on pH measurement of seawater might be what you are after.

http://scholarlyrepository.miami.edu..._dissertations

[bertoni]

That's going to come down to money invested. The Apex might have issues with electrical interference, etc. What does the manual say about the error rating? Research grade meters probably are expensive. My little Oakton hand-held was rated to ±0.01 ppm, at least in theory, and it was only $150 or so, if that's good enough.

[karimwassef]

0.01 ppm equates to what in pH?

[bertoni]

Argh! I mean ±0.01 pH units, not ppm. Sorry!