Measuring pH of DI water

[DJ88©]

Have a quick question for you. I hope that the answer doesn't take up a lot of your time. :)

Can you actually measure the pH of RO/DI water using the Pinpoint meter?

To me by DeIonizing the water you are making it very difficult for the meter to actually determine what the pH is. I am trying to get this all straight in my head.

I don't know for sure how the pinpoint measures my water but I have it in my head that a measurement involves measuring Ions in the water(or somethig like that) Am I out to lunch?..

I wish I knew all the proper terminology but I am a techie. ;) :D The chemistry stuff slips past me some days..

Basically can you get an accurate measurement of pH with the meter I am using? If there is a link where I can learn about this I'd be happy with that, so I can sit and study it if you can't point me in the right direction without taking up too much of your time. I have tried searching for an answer but keep finding similar questions but am still kinda foggy on the whole thing.

Thank you very much.

[DJ88©]

Well before I take up any of your time I found a neat little site that explained how the probe measures the electric potential between a probe sensetive to H+ ions and a reference probe. So basically measuring the pH of deionized water is very difficult with the meters we are using. That is my take on it. Am I far off?

If you have any sources online that goes more indepth I'd enjoy reading them.

Thanks for your time.

[Randy Holmes-Farley]

DJ:

<< I don't know for sure how the pinpoint measures my water but I have it in my head that a measurement involves measuring Ions in the water(or somethig like that) Am I out to lunch?.. >>

I'm happy to go into detail about how pH electrodes work, but it sounds like that isn't really what you want.

Here's a link with some basic information about how pH electrodes work. If you want more detailed info (like how the glass senses the protons, etc.), I'd be happy to oblige.

http://www.thermo.com/eThermo/CDA/Technology/Technology_Detail/0,1213,1000000010143-11275-161-161-1000000010143,00.html


Measuring the pH of pure water is problematic for a variety of reasons. These include real pH changes caused by just about any contaminant around (including atmospheric CO2) and phantom changes (e.g., water motion around the electrode). The root of all of these problems is that there is very little buffering capacity in pure water, and the pH is free to easily drift over the range from about 5-9.

So the short answer is that measuring the pH of pure water is difficult. However, if you put a pH electrode in "pure" water and get a pH reading that is stable, it is likely a real reading, and can be used for most purposes.

I've measured my RO/DI water and the pH is on the high side. Something real is in the water that is raising the pH, though I've not tried to determine what it is, or whether it comes through the RO/DI, or is only coming into the water as it sits in my plastic trash can.

[DJ88©]

Thank you very much. Your link was a slightly condensed version of what I found at ph-measurement.co.uk (http://www.ph-measurement.co.uk/index.htm) . Your take on it helped cement it in my head. :)