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  for Metal Finishing since 1989
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Checking ph of DI water accurately

I would like to be able to check the ph of DI water to guarantee it to be from 6.5 to 7.5 ph. Can I do this with a handheld ph meter? Some people said to add potassium chloride. use:Humidity testing in a chamber using DI, need to certify ph of water.

David Pontefract
- Akron, Ohio, USA
2001

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I used to measure the pH of water for humidity testing as well. I have concluded that a laboratory meter is much better than a hand-held one. Spend the extra money to get a more reliable meter. A big problem with measuring pH of pure water in that range is that carbon dioxide from the air can dissolve into the water sample and change the pH.

Tim Neveau
Rochester Hills, Michigan
2001

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David -

I agree with Tim to use the better pH meter. Also, be sure to calibrate the meter regularly, using certified buffer solutions to be certain of the accuracy.

Cynthia L. Meade
- Sylvania, Ohio, USA
2001

Measurement of pH is fine but to measure very pure solutions such as DI water the meter you will need to use will be at the top end of the market. The transfer of solutions to this meter can be a source of minor contamination which drastically affects results. Conductivity to measure total dissolved solids is a much more effective way of measuring the purity of DI water. The hand held meters of this type are much more reliable than the hand held pH probes. If you are only to use 1 type of measurement I would advise conductivity but obviously both is the best course of action.

Ciaron Murphy
- South Wales
2001