Calibrating electronic Ph meter

[Netlist]

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

 

[SY]

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.

 

[Netlist]

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

 

[RDL2004]

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.

 

[Juergen Knoop]

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

 

[SY]

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.

 

[XEAGLEKEEPER]

A company called Hach sells the buffer solutions
http://www.hach.com/

Dave

 

[Netlist]

Thanks a lot everyone.
That's a wealth of useful information.

/Hugo