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Distilled vs. Purified vs Deionized Water for pH test

sister verona

sister verona

My pH tester says use distilled water for calibration. The buffer powder says use deionized water. Will purified water work just as good?  They all have their differences.
 
I have had the same question. I know there are
calibration solutions for the pH meters, but I
haven't got to the grow store yet to check it out.
 
Hopefully someone who knows more than I will
respond to your question.
 
Distilled water and deionized water should each have a pH of 7.0.  If you're doing single point calibration, you'll need the pH to be 7.0, i.e., you can't use pH 6.5 and adjust because the unit will treat whatever liquid the probe goes into as "7.0."  Anything other than 7.0 won't result in accurate calibration.
 
I believe both distilled and deionized water will react fairly aggressively with carbon dioxide, resulting in a lowering pH. This means once exposed to the atmosphere, they will absorb the CO2 and the water pH will trend acidic.  For this reason, I wouldn't (and don't) use either, but use a calibration solution instead.  If I didn't have any solution, I'd probably use a freshly opened bottle of one of the others, but wouldn't continue to use it later after it had been opened. But I'd pH test it first (even if the calibration wasn't updated first) to see if it appeared in range.  Who knows what the water may or may not have experienced since treatment.
 
Disclaimer:  I'm no chemist, but this is my understanding of it.  :)
 
Both should work just fine as your precision does no need to be as high as in labs anyway. Some important things to keep in mind though, if you have a 2 point calibration unit, make sure you always use calibration buffers that are as close as your seeking pH will be (probably 7 and 4) because otherwise your readings may really lack in accuracy. At calibration time, pour a little bit of eah of your buffer solution into clean recipients (to avoid contamination of the whole buffer bottles!) and rinse your electrode 2-3 times with a small amount of the needed buffer prior to calibrate. When storing your unit, always add a small piece of sponge or towel paper soaked in pH 4 in the cap to make sure that the electrode will not dry over time. 
 
To calibrate, I use premixed buffer solutions and 1/2 teaspoon measuring spoons. Deep enough to cover the probe bulb, but small enough to not use a lot of solution.
 
salsalady said:
To calibrate, I use premixed buffer solutions and 1/2 teaspoon measuring spoons. Deep enough to cover the probe bulb, but small enough to not use a lot of solution.
Click to expand...
 
The minimum volume required for calibration depends mostly of your pH meter model; obviously mine needs a bit more than yours SL! But it works like a charm and it's quite easy to calibrate too!
https://intl.hannainst.com/hi98128-phep-ph-tester.html
 
1/2 teaspoon? Hmmm...That must of been a re-wine typo. :Lol:. It more than likely requires a teaspoon of buffer...


What I was getting at and did not clarify, was that the shape of the spoon does affect the amount of solution needed. Some spoons are shallow and would require a tablespoon to get the probe immersed. Some spoons I have are a deep bowl, so I can immerse the probe, swirl it around and set calibration.
 
salsalady said:
1/2 teaspoon? Hmmm...That must of been a re-wine typo. :lol:. It more than likely requires a teaspoon of buffer...


What I was getting at and did not clarify, was that the shape of the spoon does affect the amount of solution needed. Some spoons are shallow and would require a tablespoon to get the probe immersed. Some spoons I have are a deep bowl, so I can immerse the probe, swirl it around and set calibration.
Click to expand...
 
Got it but at first I thought you were running cheap on buffers!!! More seriously, some devices have a really thin probe so one does not need much to get the calibration done. In the other hand some need a bit more. This is the one I use (mostly for home brewing purposes) and the probe which measure about 1 inch wide x 1/4 inch thick has to be fully submerged to achieve calibration.
 

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