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Old 06-17-2009, 10:38 PM   #1
nanok66
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Hi I have recently bought a digital pH meter to use for brewing and I hope someone has knowledge on making your own standard pH solutions for calibrating pH meters.

My idea is this; a very small amount of standard pH test solution came with my meter to calibrate it so I want to make a large amount of my own solution.

I want to mix some distilled water with an arbitrary amount of star-san and measure the pH very accurately with my meter. Now if I keep this solution in a glass bottle I don't see any reason it should change pH if left alone. It doesn't matter what exact pH my starsan solution comes out to as long as I write that number down I can always calibrate my meter to that value. Anyone see any problems with this??

Although before anyone responds I will point out the obvious problem that if I continue to make solutions off of previous homemade solutions the accuracy will begin to drift no matter what I do. So I will just say now I plan on making around a quart of the solution which will last me nearly forever if the initial idea works.

Thanks to anyone who answers!

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Old 06-18-2009, 01:52 AM   #2
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I dont think that this would be a good way to check your meter calibration. Instead use one of these.

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Old 06-18-2009, 02:57 PM   #3
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I don't do this myself but remembered the post and thought I'd share:

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Old 06-18-2009, 04:18 PM   #4
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Although it is possible to use the pH of common household liquids I don’t recommend this in the long run.

I actually bought a 500 ml bottle of 4.0 and 7.0 buffer at cynmar.com but I’m reusing the buffers: I refilled the 4oz bottles that I got from NB when I initially bought the meter and to calibrate it just put the probe in the small bottle (making sure it is at 25C) and calibrate the meter. I rinse the probe with R/O water before and after I put it into the calibration solution.

These solutions are very strongly buffered and the pH drift that comes from reusing them is very slight. Every 6-12 months I replace the 4z with fresh buffer solution from the larger bottles.

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Old 06-29-2009, 02:41 PM   #5
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Kaiser,

You are definitely correct that using home made calibration standards is probably not the way to go if you are to the point of wanting to measure pH. However, I would sugest some changes to your method of calibration. You really should be using fresh buffer every time you calibrate. What I do is pour about 15 mL of buffer in a 20 mL vial. Rinse your electrode in DI H2O and then rinse with about 5 mL of buffer. Place your electrode in the buffer and calibrate. The problem with using the buffer over and over is:
1. You are exposing your buffer repeatedly to the atmosphere.
2. You are chaning the concentration of the buffer with your H2O on the probe.
3. You are exposing the buffer to the fill solution in the electrode.
If these things are important to you or not or is up the the individual; to each his own!

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Old 06-29-2009, 03:38 PM   #6
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I agree that my method if reusing the buffer is not scientifically approved. I keep that in mind and every few month I check the drift of my buffer solutions. Last time I checked it was just 0.01. Once it gets to 0.02 I'll replace the buffers. I'm willing to accept this imprecision to save money on the buffer solution.

Kai

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