# pH Meter Calibration points?



## runswithsizzers (Oct 19, 2018)

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>?


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## cmason1957 (Oct 19, 2018)

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


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## Johnd (Oct 19, 2018)

cmason1957 said:


> 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.....


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## mainshipfred (Oct 20, 2018)

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.


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## runswithsizzers (Oct 20, 2018)

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?


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## cmason1957 (Oct 20, 2018)

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.


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## runswithsizzers (Oct 20, 2018)

cmason1957 said:


> 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.


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## Ajmassa (Oct 20, 2018)

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)


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## ceeaton (Oct 20, 2018)

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.


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## runswithsizzers (Oct 21, 2018)

ceeaton said:


> 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?


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## Bts (Oct 22, 2018)

cmason1957 said:


> 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 :/


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## Ajmassa (Oct 22, 2018)

Bts said:


> 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.


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## runswithsizzers (Oct 22, 2018)

Ajmassa5983 said:


> 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?


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## Ajmassa (Oct 22, 2018)

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


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## sour_grapes (Oct 22, 2018)

runswithsizzers said:


> 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._"
> ...



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.


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## cmason1957 (Oct 22, 2018)

Ajmassa5983 said:


> 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.


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## Ajmassa (Oct 22, 2018)

cmason1957 said:


> 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.


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## stickman (Oct 22, 2018)

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.


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## runswithsizzers (Oct 22, 2018)

cmason1957 said:


> 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.


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## ceeaton (Oct 23, 2018)

runswithsizzers said:


> 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.


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## robert81650 (Oct 24, 2018)

Hey this pH thing you guys are fretting about is not a rocket shot to the moon. After all this is home wine making and what we get as far as a pH reading on a good meter should be adequate as long as the wine tastes good and is stable for storage for several years to age.


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## runswithsizzers (Oct 24, 2018)

robert81650 said:


> Hey this pH thing you guys are fretting about is not a rocket shot to the moon. After all this is home wine making and what we get as far as a pH reading on a good meter should be adequate as long as the wine tastes good and is stable for storage for several years to age.


Maybe some people are born knowing the definition of "a good pH meter" and how to use one, but I wasn't. Sorry to bother you.


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## Boatboy24 (Oct 24, 2018)

ceeaton said:


> 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.



Craig: How do you store the probe? My initial meter purchase was a pHep 5, which is supposed to be a decent meter (about $85 at the time). It would never settle on a reading. I've since gone through a couple cheap (sub $20) meters. They calibrate perfectly for a bit, but eventually conk out after a year, maybe less. I want something reliable, but I'm starting to feel like storage is key. I've been using the 'pen' style meters with storage solution in the lid. What do you use, how often do you calibrate/use your meter, and what is your process. I'm thinking of a MW meter, but don't want to spend the $$ if it is going to crap out on me after a year.


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## ceeaton (Oct 26, 2018)

Boatboy24 said:


> Craig: How do you store the probe? My initial meter purchase was a pHep 5, which is supposed to be a decent meter (about $85 at the time). It would never settle on a reading. I've since gone through a couple cheap (sub $20) meters. They calibrate perfectly for a bit, but eventually conk out after a year, maybe less. I want something reliable, but I'm starting to feel like storage is key. I've been using the 'pen' style meters with storage solution in the lid. What do you use, how often do you calibrate/use your meter, and what is your process. I'm thinking of a MW meter, but don't want to spend the $$ if it is going to crap out on me after a year.


The MW 101 series has a tube with a rubber seal that seems to keep the storage solution from evaporating and leaving a salt like residue behind. I think when the membrane part of the probe dries out it may plug with whatever residue is in the solution you store it with, then needs a cleaning to get rid of it. If you can keep it from drying out or the solution concentrating, I think that's half of the battle. Mine is stored in the cool basement, but I bring it and my solutions up the day before I test (unless it's summer, where the temps between the basement and upstairs are rarely more than 10*F difference) so thanks for the reminder, I'm hoping to get some wine "stuff" done tomorrow while it is raining. I've only had mine a couple of years, but I think the nice thing is the probe is a stand alone item you can buy if it goes south on you. Mine was just over $100 shipped. You can get them cheaper, but I bought mine because it didn't have the temperature correction function, and I think that is what went haywire on my Hanna meter, especially if the temperature wasn't stable (ie. I forget to bring it upstairs that night before testing). Hope that helps. You are more than welcome to try mine out, but I don't have a car this weekend (18 yr old daughter hijacked it) so you'll have to drive up here!


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## rsportsman (Nov 28, 2018)

runswithsizzers said:


> 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.
> 
> ...


A good trick is to use cream of tartar, AKA potassium hydrogen tartrate (KHT), to check your accuracy of calibration. Add 1/8 tsp cream of tartar (grocery store stuff is fine as long as it's pure) to 20 mL distilled water and mix well for about 30 seconds. This provides a "saturated solution" of KHT. A properly calibrated pH meter should read this solution as pH 3.56 at 25C. (doesn't change much with +/- 5C). I am usually OK with a reading between 3.50 and 3.60. Discard this solution after 24 hours. - Rich from Vinmetrica


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## runswithsizzers (Nov 28, 2018)

I have since replaced the Hanna Checker mentioned in my original post with a ThermoWorks pH meter, # 8689. The ThermoWorks meter is more accurate than the Hanna (+/- 0.05 vs. +/- 0.2 pH), and the ThermoWorks also allows for 3-point calibration. I paid $80 (US) for the ThermoWorks #8689 (on sale) compared to $58 for the Hanna at my semi-local brew store. <link here>

The calibration instructions for the 8689 were not entirely clear, so I called for ThermoWorks clarification. I was amazed when a real person answered the phone and he answered my questions in good English!


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