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Old 13th April 2007, 04:14 PM   #1
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Default Calibrating electronic Ph meter

Is there a way to calibrate an electronic Ph meter?
A liquid with a known stable Ph value would do the trick, only what should I look for?

/Hugo
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Old 13th April 2007, 04:38 PM   #2
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You want two buffer solutions at pH values which are 3 or 4 apart (for example, pH = 5 and pH = 8). Any chemical supply place will have them.
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Old 13th April 2007, 04:51 PM   #3
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Thanks, I know a few in town.
As for the trimming, there's only one pot so both liquids will only be able to make me adjust indicatively.

/Hugo
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Old 13th April 2007, 08:12 PM   #4
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You need what is called "buffer solutions". They are made specifically for calibrating pH meters.

They come in many pH values. For better meters with 2 point calibration you usually use something like 4 and 10.

For meters with only 1 point calibration (which it seems yours is) it is usually best to pick a buffer value near the pH which you will be measuring.

Also, temperature will affect the pH reading, more expensive meters will have built in temperature compensation.

I think the buffers must be at a certain temperature to be the specified pH, probably 25C.
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Old 13th April 2007, 08:21 PM   #5
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afaik, one point trimming is better done with a pH 7 buffer
because the probe change their asymmetry far more, than their slope
I have had several used probes, even really cheap ones, with nearly perfect 57-59mV/pH at room temperature, but asymmetry up to hundreds of mV in one case
I think you can also use pH 4 or 6,81 buffers, this shouldn't matter with a simple pH-stick
just don't use dest. water as some people recommend
it has not pH 7 and the probe will give no reliable readings with such unbuffered water
regards
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Old 13th April 2007, 08:50 PM   #6
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That's exactly it- "buffer" is the key word. Because pH is logarithmic, a deviation of 1 pH unit on either side of neutral (ph= 7) is a very, very tiny change in hydronium/hydroxyl ion concentration. Purified water will NOT work. As with amplifiers driving a load, a buffer is called for.
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Old 13th April 2007, 11:27 PM   #7
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A company called Hach sells the buffer solutions
http://www.hach.com/

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Old 14th April 2007, 06:46 AM   #8
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Thanks a lot everyone.
That's a wealth of useful information.

/Hugo
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