Proper way to take a PH sample?

[Willum]

I have been adjusting my water and checking PH with a meter for a while now and I have question about the proper way to take a sample for a PH reading. Should I take liquid only or should some of the grist be in the sample?

I have tried it both ways and the it seems if there are grains in the sample the PH rises as it cools.

Every source I have read says take a room temperature sample, but during the wait for the sample to cool I have noticed a very small difference (~.03) between 150 and room temperature if the sample is all liquid and almost a .2 point difference when the sample has grain in it.

My ph meter (Milwaukee pH56) has ATC, but I don't trust it because the PH drifts when the ATC symbol is showing.

 

[ajdelange]

Every source I have read says take a room temperature sample, but during the wait for the sample to cool I have noticed a very small difference (~.03) between 150 and room temperature if the sample is all liquid and almost a .2 point difference when the sample has grain in it.

I was about to direct you to the pH Sticky at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/) but when I went there to check the URL I see you not only have read it but 'Liked' it (thanks). As it says there, it shouldn't matter whether there are a few bits of grain or not present. The true pH reading should shift about 0.0055 pH/°C change in temperature. Going between room temperature (20° C) 150 °F (65.5 °C) thus should result in a shift of about 0.25 so I mystified as to why you see a difference between the two readings (neither of which corresponds to what the theory predicts). The meter reads hydrogen ions and they move through the liquid so the meter reads the liquid whether grain is present or not. The only possible explanation I can think of is that a blob of gelatinous grain has blocked the electrode's junction. This is a common cause of pH meter measurement problems. I would, therefore, recommend checking that the junction is clear. Junctions come in different forms. New (to me anyway) and apparently quite popular in low priced electrodes is the cloth junction - just a strip of rag which communicates between the reference section of the interior of the electrode and the outside.

My ph meter (Milwaukee pH56) has ATC, but I don't trust it because the PH drifts when the ATC symbol is showing.

Stability is always an issue with inexpensive meters but here you are suggesting that the meter is not stable with ATC on and stable with it off. Is that indeed the case? If so then you need to investigate further. Given that the electrode voltage is stable (as indicated by stable reading with ATC disabled) instability when ATC is on indicates that temperature readings are erratic. Are they?

ATC does have its limitations with normal electrodes (isoelectric pH close to 7) but even if you have an unusual one (isoelectric pH not that close to 7) the performance is OK within a few degrees of the calibration temperature. It is best to use ATC (assuming it works) but to calibrate and measure with buffers and samples within a few degrees of one another.

 

[Willum]

I was about to direct you to the pH Sticky at https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/) but when I went there to check the URL I see you not only have read it but 'Liked' it (thanks). As it says there, it shouldn't matter whether there are a few bits of grain or not present. The true pH reading should shift about 0.0055 pH/°C change in temperature. Going between room temperature (20° C) 150 °F (65.5 °C) thus should result in a shift of about 0.25 so I mystified as to why you see a difference between the two readings (neither of which corresponds to what the theory predicts). The meter reads hydrogen ions and they move through the liquid so the meter reads the liquid whether grain is present or not. The only possible explanation I can think of is that a blob of gelatinous grain has blocked the electrode's junction. This is a common cause of pH meter measurement problems. I would, therefore, recommend checking that the junction is clear. Junctions come in different forms. New (to me anyway) and apparently quite popular in low priced electrodes is the cloth junction - just a strip of rag which communicates between the reference section of the interior of the electrode and the outside.



Stability is always an issue with inexpensive meters but here you are suggesting that the meter is not stable with ATC on and stable with it off. Is that indeed the case? If so then you need to investigate further. Given that the electrode voltage is stable (as indicated by stable reading with ATC disabled) instability when ATC is on indicates that temperature readings are erratic. Are they?

ATC does have its limitations with normal electrodes (isoelectric pH close to 7) but even if you have an unusual one (isoelectric pH not that close to 7) the performance is OK within a few degrees of the calibration temperature. It is best to use ATC (assuming it works) but to calibrate and measure with buffers and samples within a few degrees of one another.

Thanks for the reply. I have read your calibrating thread as you mentioned and I do the exact process right before every brew. I am really starting to question the accuracy of meter all together. I have to calibrate it maybe 4 or 5 times before it stops drifting.

For example, I turn it on put it in 7.01 solution and it is reading lets say 6.99 steady. I do the process exactly as written out in the link above. Clean electrode with DI water and a paper towel. Put it back in the 7.01 solution and it is now drifting up and maybe it will stop, sometimes I don't wait to see. When it hits 7.10 I do the process over. I have even dumped the solution a few to ensure DI water did not get into.

Finally after a few times calibrating it seems to stabilize. Also this is after leaving it in the original solution for 15 minutes before I start the calibration process. I can't help think the meter is not supposed to behave this way...

 

[ajdelange]

Finally after a few times calibrating it seems to stabilize. Also this is after leaving it in the original solution for 15 minutes before I start the calibration process. I can't help think the meter is not supposed to behave this way...

No, it isn't but, unfortunately, this kind of behavior is typical of under $100 meters and I'm not sure that it isn't also typical of somewhat more expensive meters but as home brewers tend to use under $100 items we hear about it more from them. At least things apparently eventually settle out for you. I know it is a great inconvenience to have to wait and repeatedly recalibrate but there really isn't much point in taking readings with a drifting meter.

 

[Yooper]

I have a milwaukee pH 56. I've sent it back three times, and gone through five electrodes. I was pleased with electrode #6, for several months. It worked again for about 3 months. Today, it wouldn't calibrate (said "wrng" on both buffers) but then it did and it drifted like crazy. Each time, I'd recalibrate. It would seem to be ok for a few moments, but then drift again.

I do not abuse it, it's never been subjected to temperatures above 75 or below 55, and I calibrate it as directed. I have storage solution, electrode cleaner, etc.

It's really a piece of crap. Even the replacement electrodes aren't always very good, but I did get a good one last time. Until it suddenly didn't work any more.

 

[Homercidal]

why not use some laboratory instrument?

$$$

 

[Willum]

I have a milwaukee pH 56. I've sent it back three times, and gone through five electrodes. I was pleased with electrode #6, for several months. It worked again for about 3 months. Today, it wouldn't calibrate (said "wrng" on both buffers) but then it did and it drifted like crazy. Each time, I'd recalibrate. It would seem to be ok for a few moments, but then drift again.

I do not abuse it, it's never been subjected to temperatures above 75 or below 55, and I calibrate it as directed. I have storage solution, electrode cleaner, etc.

It's really a piece of crap. Even the replacement electrodes aren't always very good, but I did get a good one last time. Until it suddenly didn't work any more.

You pretty much described my exact problem. I will second that it is a piece of crap.

 

[Bassman2003]

I have had good luck with this meter. The cost of entry is low but it is performing well (as far as I know). Just take the batteries out in between uses as they drain.

http://www.ebay.com/itm/pH-Temp-C-F...164?pt=LH_DefaultDomain_0&hash=item4acbd3b104

 

[ajdelange]

With those specs it is hardly better than papers. The price is right, though.

 

[Bassman2003]

Well I guess I should not post where I know little about the subject... Papers never worked for me so it is a lot better than paper in my book. I am not prepared to spend $100+ so I can live with just having "a meter".

 

[ajdelange]

The main question would be as to it's stability. If it is stable then it is useable. I really don't know what 'accuracy of 0.2 pH' means. I suspect that it means that the reading in a calibration buffer wanders such that it rms value is 0.2 pH. You can easily check the stability by simply making repeated readings in one of the buffers over time and writing them down. If the device reading doesn't change over a period of half an hour or more it is definitely useable. Even if it holds for only 15 minutes you can use it but you will need to recalibrate it each time you take a reading. And that would give you a better picture than papers.

 

[Bassman2003]

I will test it and see. I calibrate it before each brew and it usually hits the pH 4 & 7 targets before I hit the calibrate button.