pH Meter Calibration points?

[runswithsizzers]

I recently bought my first pH meter - a Hanna Checker, Model HI98103 <details here> Mine is the newer model, and accuracy is +/- 0.2 pH. I am using it for both juice/must/wine and TA (total acid) titrations.

My model is capable of either one-point or two-point calibration. Hanna provides calibration material at pH 4.01, 7.01, and 10.01, and I believe the meter calibration process relies on using one (or two) of these levels. If doing a two-point calibration, one of the levels must be 7.01.

In <this thread> ibglowin says
"[Use] Only the 4.0 since the wines pH is always between 3.2 - 3.9. If you use 4.0 and 7.0 your basically calibrated then between those values. Your better off with a single point 4.0 since your samples is usually so close to the 4.0 anyway."
... to which grapeman replied,
"Unless you use your meter for doing a TA test where you go to 8.2 and then you need to calibrate using both."

Following that advice would require calibrating my pH meter at 4.0 for wine and juice (one point), and at 7.01/10.01 (two-point) for TA titrations, right? While that is doable, it also would require a lot more time and materials to recalibrate every time I switch from wine to a TA titration. Which I would prefer to avoid unless necessary.

Does anyone know just how much accuracy suffers at pH 3.2, and at pH 8.2 - if my meter is calibrated from 4.0 to 7.0?

Maybe it would be best to have two pH meters, one calibrated for juice/wine and one for TA titrations? They are cheap enough. If I get another one, I might consider <this one> which has no better accuracy than my Checker, but is made to be more reliable for juice/wine because it protects the probe better from particles. And it comes with pH 3.0 and 7.0 calibrators.

On the other hand, maybe it makes more sense to own one good pH meter, which can hopefully store two calibration curves, rather than two cheap meters? Like <this one>?

 

[cmason1957]

I would just do the 4 and 7 calibration. Otherwise you will spend all your time calibrating and not measuring.

 

[Johnd]

I would just do the 4 and 7 calibration. Otherwise you will spend all your time calibrating and not measuring.

I second that approach, it’s all I ever do with my Vinmetrica, it’s never let me down.....

 

[mainshipfred]

I think you need at least a 2 point calibration and that's all most do. Lately if I want to double check my meter I will use the 4 and 7 then with a fully saturated solution of cream of tartar and distilled water check the meter. This solution will have a ph of 3.56 which is a little closer to your wine. This test is in the Vinmetrica handbook.

 

[runswithsizzers]

To mainshipfred, thanks for tip about using cream of tartar to check pH at 3.56!

To all; RE: the quote by ibglowin in my opening post "Your better off with a single point 4.0 since your samples is usually so close to the 4.0 anyway." (his words, not mine)
Can anyone link to a source that confirms by experiment or theory why a single point calibration would ever be more accurate than a two point calibration which includes the same level as the single point?

Hanna's website recommends using calibrator levels which bracket the target value (https://blog.hannainst.com/ph-meter-calibration), but also says: "... for 99% of the time buffer 7 and buffer 4 solution are the two you need to perform a calibration." (https://hannainst.com/knowledge-base#calibratemeter)

While it is possible a single-point calibration at pH 4.0 might provide adequate accuracy for measuring at pH 3.0-4.0, I am having trouble finding any evidence to support the theory that adding a second point to the calibration at pH 7.0 would have a negative effect at pH 4.0. My supposition would be that a two-point cal (pH 4.0 and 7.0) would be MORE accurate at pH 3.0 than a single point cal at pH 4.0. Can anyone confirm or deny?

 

[cmason1957]

No clue why anyone would say a single point calibration is all that is required. You are creating a line, one solution sets the y-intercept, the other sets the scope of the line. Both are required for correct readings. One is never as accurate as two is my stance.

 

[runswithsizzers]

No clue why anyone would say a single point calibration is all that is required. You are creating a line, one solution sets the y-intercept, the other sets the scope of the line. Both are required for correct readings. One is never as accurate as two is my stance.

Agreed. I worked in a clinical laboratory for 20 years, but I was never comfortable with the concept of a single point calibration. A very few assays were based on a one-point calibration, but those we reported as positive or negative and not as a number.

Yet Hanna offers the option of a single point calibration on their pH meters. Hanna does strongly encourage using a two point calibration, but since they offer 1-point as an option, there may be some situations where that gives acceptable results? I have contacted Hanna's technical support for clarification and will report back if they provide any relevant information.

 

[Ajmassa]

I don’t see why it wouldn’t be just as accurate if calibrating buffer at 4.0 and only reading wine samples in the 3-4 range. Theoretically it Should be dead on. But as soon as out of that range (TA test) would start walkin right away

When I do quick checks I just read a 4 buffer and 7 buffer. If I get 4.0 and 6.9 then I’m close enough to check wines that I know where they ‘should be’.
New must, post MLf, and when adjusting acid is when I don’t play games tho. my meter only reads one decimal giving more wriggle room (only negative aspect of Milwaukee ph55)

 

[ceeaton]

I normally do a two point check since that what my Milwaukee (MW 101) meter suggests. Additionally you may want to think about getting another solution (https://www.piwine.com/ph-3-buffer-solution-4-oz.html) with a pH of 3.0. I use it after calibration to double check that nothing went too far awry with my two point calibration. If it reads too high or low, I adjust my readings slightly either way (depending on the pH) or better yet, perform the calibration again until my readings on the 3.0 solution are closer.

 

[runswithsizzers]

I normally do a two point check since that what my Milwaukee (MW 101) meter suggests. Additionally you may want to think about getting another solution (https://www.piwine.com/ph-3-buffer-solution-4-oz.html) with a pH of 3.0. I use it after calibration to double check that nothing went too far awry with my two point calibration. If it reads too high or low, I adjust my readings slightly either way (depending on the pH) or better yet, perform the calibration again until my readings on the 3.0 solution are closer.

When you say your pH 3.0 sometimes reads "too high or low" I would be curious know by how much - pH 0.05? 0.5? 1.5?

And if you decide to recalibrate again, is one repeat usually enough to get the accuracy you want at pH 3.0 - or do you sometimes have to recalibrate multiple times?

 

[Bts]

No clue why anyone would say a single point calibration is all that is required.

I suspect it's because some of us are using garbage $10 meters off ebay that only have one calibration point. If you calibrate at 7, then 4 will be way off, or vice versa. However if you calibrate at 4(or better yet 3.56 with tartarric) then your target PH of 3.65 is so close to your calibration PH that even a the cheap chinese junk meters are accurate enough. At least they're better than trying to read a PH strip stained red with wine so the color is nowhere near anything on the chart :/

 

[Ajmassa]

I suspect it's because some of us are using garbage $10 meters off ebay that only have one calibration point. If you calibrate at 7, then 4 will be way off, or vice versa. :/

Maybe. I’m curious to hear @ibglowin chime in since he was the one quoted. I do suspect he had legit reasons for saying so. He’s a chemist by trade and a moderator on the forum. Not the type to post baseless info.

 

[runswithsizzers]

Maybe. I’m curious to hear @ibglowin chime in since he was the one quoted. I do suspect he had legit reasons for saying so. He’s a chemist by trade and a moderator on the forum. Not the type to post baseless info.

Yes, it was his post that prompted me to start this thread. If I understand his post correctly, he seems to be saying that a single point calibration is actually better than a 2-point calibration (?)

Yet literature offered by the manufacturers of these instruments all say a 2 point calibration is aways "better" than single-point, and they don't mention any exceptions. How much better, they don't say, so it may be that close enough is good enough for some/many situations.

I just got an email back from Hanna technical support today which tells me:
"A 2 point calibration is always better than just a 1 point calibration."

That email also said:
"If possible you would want to bracket your calibration around your expected measurement range."
and
"The accuracy is from the whole range of the meter which is 0 to 14ph."

What I am trying to understand is: If I get the same +/- accuracy across the whole range of measurement, then why the advice to bracket my calibration around my expected value.

For us winemakers, if we choose the standard pH 4.0 and 7.0 calibrators, few if any of our expected values are bracketed. But having been told I can expect the same +/- 0.2 pH accuracy outside of the brackets, should I care?

 

[Ajmassa]

Can you post the link of the thread that the quote is from?

 

[sour_grapes]

That email also said:
"If possible you would want to bracket your calibration around your expected measurement range."
and
"The accuracy is from the whole range of the meter which is 0 to 14ph."

What I am trying to understand is: If I get the same +/- accuracy across the whole range of measurement, then why the advice to bracket my calibration around my expected value.

They did not say that you get the same accuracy across the whole range. They said that the cited accuracy is computed across the whole range. It is very likely that the accuracy is better within the bracketed range than the figure cited across the whole range.

 

[cmason1957]

Can you post the link of the thread that the quote is from?

https://www.winemakingtalk.com/threads/ph-meter-calibration.17430/#post-166662

I am going to guess that the logic is, since we generally measure around 3.2-3.8, if the 4.0 is on, then those should be as well. And I suppose so, but it is so easy to check both, true you aren't bracketing where the wine is, but someone suggested doing a ph 3.0 check, which would bracket. I think I also have to throw in here that a ph meter +/- 0.2 ph, isn't quite as good as I would like one to be, better than trying to read paper.

 

[Ajmassa]

https://www.winemakingtalk.com/threads/ph-meter-calibration.17430/#post-166662

I am going to guess that the logic is, since we generally measure around 3.2-3.8, if the 4.0 is on, then those should be as well. And I suppose so, but it is so easy to check both, true you aren't bracketing where the wine is, but someone suggested doing a ph 3.0 check, which would bracket. I think I also have to throw in here that a ph meter +/- 0.2 ph, isn't quite as good as I would like one to be, better than trying to read paper.

Thanks. I assumed +\- 0.2 was a typo at first. But the link provided confirmed it. Seems like a lot. Went ahead and checked my meter’s specs.
+/- 0.1 Good enough for me.

Pretty ironic actually- with all the focus on accuracy with extra calibrating at 4,7 and 10 with a 3 checker and whatnot, when Hannah can’t guarantee within .2.

 

[stickman]

When you calibrate, the instrument is determining the slope of the electrode response to the buffers or standards, which is the millivolts per pH unit. The slope of the electrode will not be consistent across a range of measurement, in other words, the slope is different between pH7 and 4 when compared to the slope between pH7 and 10. The greater the range between calibration points, the greater the measurement error. More expensive instruments will have options for calibration at additional points, between 3 and 4 would be ideal, but for our purposes the 7 to 4 calibration is reasonable, and maybe add the third point of 10 for those using the pH for acid titration.

The question about the single point calibration is still open, it really depends on the software in the instrument, it may be maintaining the previous slope in memory and just offsetting the response based on the single point calibration. I'm not sure, so it doesn't make sense to speculate any further.

I've used the single point calibration, but only when I've used the 7 and 4 calibration in the past few days and I'm comfortable that the meter is stable, I might come in with the pH4 buffer and see .02 pH error, so I press the cal button and it zeros it out, good enough for me.

 

[runswithsizzers]

https://www.winemakingtalk.com/threads/ph-meter-calibration.17430/#post-166662

[...] I think I also have to throw in here that a ph meter +/- 0.2 ph, isn't quite as good as I would like one to be, better than trying to read paper.

I agree. I bought this meter at a brick and mortar brew shop about 15-20 miles from where I live. Before buying the meter I had checked the specs online, and their website said the accuracy was +/- 0.02 pH. After I got it home and discovered the discrepancy in specs, I emailed them about it. They said Hanna redesigned the pH meter, downgraded the specs, but kept the same model number. The specs on their website were for the older model. They were very apologetic about the out-of-date specs on their website and offered to refund my money. I suppose I should take them up on that offer.

Like you say, +/- 0.2 pH is better than pH paper, but there is still some guesswork when making decisions based on borderline readings. So I am shopping for something more accurate.

 

[ceeaton]

When you say your pH 3.0 sometimes reads "too high or low" I would be curious know by how much - pH 0.05? 0.5? 1.5?

And if you decide to recalibrate again, is one repeat usually enough to get the accuracy you want at pH 3.0 - or do you sometimes have to recalibrate multiple times?

Sorry for the delay, busy at work...

.05 to .10 is what I'm looking for before recalibrating. Of course, spot on is always nice. I usually am within .02 or less. (I've got an MW101 meter, love it. I think a meter without the temperature calibration is the way to go. My old Hanna would jump all over the place until the probe became stable with the temperature of the solution)

http://www.milwaukeeinst.com/site/p...0-products-g-standard-portable-meters-g-mw101

I've had to recalibrate multiple times only once. I think I had rinsed my probe with tap water, which around here is very high pH and very high in carbonate hardness (200 ppm and higher, lot's of limestone). I try and rinse it in RO or distilled water before placing it in the reagent (whether 3.01 or 4.01 or 7.01). I try my best to use the solutions as much as I can as I'm usually testing multiple samples of wine at the same time.