Accuracy of ph calibration solutions

[adam01]

I have to buy some more calibration solutions. I bought Atlas Scientific solutions
last time. I was reading that the accuracy of some solutions available is not great.

Does anyone recommend a particular solution maker ?
I use a MW101 meter. I'm trying to use distilled water + minerals to build water, since
our water supply seems to be blending two lakes water and producing a widely varying
mineral readout compared to prior months.

 

[wardens355]

I would guess something from Cole Parmer would be reliable, but more expensive. If the product is certified by a lab and does not appear to have any contamination, I would imagine it is fine. Pour the calibration solutions into smaller containers that are used for calibration - do not dip a probe into the bottle of stock calibration solution, as this may cause contamination, especially in the neutral solution. And check the expiration to make sure it isn't out of date.

 

[ajdelange]

The buffers you buy should be labeled pH 4.01 ± 0.02 and pH 7.00 ± 0.02. There are ± 0.01 buffers but their use is not justified in most brewing applications, especially not with a meter like an MW01. There are several manufacturers, e.g. Hach, Thermo/Orion... You can get buffers directly from the manufacturers or a lab supply store. Particularly handy are the capsules of powder which you mix with 50 or 100 mL of DI water just prior to use (Hach, pHydrion).

 

[user 141939]

The ones that come with Certificate of Analysis are gonna be more accurate. I was looking the other day and realized it is cheaper to not buy these from a place like amazon.

http://www.coleparmer.com/Category/Oakton_pH_Buffer_Solutions/14716

 

[adam01]

Wow, two accuracy levels. I've not seen +- .02 buffers. I've seen +- .01, like the oakton referenced. I've also seen the hydroponics labeled versions with no accuracy level stated.

Yes, some Amazon products are definitely more expensive. THis is probably the ballpark
for what I want.
Hach Ph 4.01 500ml

But there are these that are not clear on the accuracy.
LSS Ph 4.0 500ml

 

[trentm]

I was under the impression you should use the same brand of calibration solutions as your meter. Perhaps that's just to promote sales. I also use a MW101 and get the Milwaukee calibration solutions from Cynmar.com, $8 for 230ml.

 

[ajdelange]

You certainly can do that but given that you have a good meter the ultimate determinant of the accuracy of your measurements is the tolerance of the buffers. A meter that can measure voltage to about 0.5 mV rms and temperature to about 0.5 °C measures, relative to its buffers, to an accuracy of a little better than 0.02 pH (at mash pH - it does depend on the pH measured). If the buffer tolerance is ±0.02 the total error will be about ±0.03. If the buffer tolerance is ±0.01 the total will be about ± 0.022, if it is ±0.05 total accuracy will be about ±0.054 and if the buffer tolerance is ? then then measurement accuracy will also be? A good meter here is defined as being one that is stable i.e. exhibits and rms deviation with respect to its calibration buffer reading of about 0.01 pH over half an hour or more. If you have an unstable meter then I suppose it doesn't matter much whether you use buffers of uncertainty ±0.02 or ±?. If you have a good meter then you should use buffers rated ±0.02 or better.

 

[CyclingCraig]

I have the MW102 and use the Powder Pillows that AJ suggested.

They worked out GREAT for me

It has a MUCH longer shelf life and is easy to mix up fresh solutions each brew day:

HACH Powder Pillows

 

[adam01]

Where are you getting DI (deionized) water ?

I figure that getting that plus the pellets is more expensive than the solutions themselves.

 

[ajdelange]

DI water is typically $0.99/gal. at the drugstore.

 

[adam01]

Oh, distilled water, yes.
When I hear of DI water, I think ultra-pure water for chip making.

 

[ScrewyBrewer]

I bought the HANNA pH meter and their 4.01, 7.01 and 10.01 calibration solutions. I'm pretty fanatical some may say about my brewing but if a solution isn't outdated I'm not too concerned about being off +-.02 when my target pH range is 5.4 to 5.6.

 

[ajdelange]

And you'd be happy with a thermometer that was off 3 or 4 degrees because saccharification temperature is between 142 and 157 °F?

 

[adam01]

So Ive read that:

• the pill buffers have a shelf life of 5 years unopened.
• the pill buffer prepared solution has a shelf life of 2-3 weeks ?
• The premade solutions have a shelf life of 2 years.

This makes the pill buffers less desirable if you brew monthly or bimonthly.
Most sites don't explicitly state the shelf life of their products, so some may be different.

 

[user 141939]

And you'd be happy with a thermometer that was off 3 or 4 degrees because saccharification temperature is between 142 and 157 °F?

+/- 0.02 for a range of 0.2 is a 10% error. In your temperature scenario you are talking about a 20-27% error. So I think your hypothetical scenario is slightly exaggerating screwybrewers hypothetical scenario.

Personally I'd use expired buffers if they were stored properly. My experience is that they don't just poof and stop working at the exp. date. I mean I wouldn't keep using them for years and years or anything...,


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[user 141939]

Double post

 

[ajdelange]

So Ive read that:

• the pill buffers have a shelf life of 5 years unopened.
• the pill buffer prepared solution has a shelf life of 2-3 weeks ?
• The premade solutions have a shelf life of 2 years.

This makes the pill buffers less desirable if you brew monthly or bimonthly.
Most sites don't explicitly state the shelf life of their products, so some may be different.

Can't say I follow that. You buy a box of the capsules and use 12 - 24 of each per year depending on whether you brew monthly or twice per month assuming that you decide you want to make new buffers each time you brew. 60 - 120 caps is a 5 year supply. You buy that many and you are covered for 5 years. You buy a cubitainer of buffer and withdraw 50 mL each time you brew. You must now use the rest of the cubitainer in less than 2 yrs because the buffer shelf life is reduced once the container is opened. Certainly the pre-mixed buffers are easier to use but the caps give you the advantage of having fresh buffer each time you use one. Which is more economical will depend on how often you brew and will determine which is the most cost effective. I'm sure the caps are more expensive but better meed my personal needs. Others will have to make their own decisions.

PS: The caps I use don't have anything like 5 years shelf-life. More like 3 but I don't have them handy to check.

 

[ajdelange]

+/- 0.02 for a range of 0.2 is a 10% error. In your temperature scenario you are talking about a 20-27% error. So I think your hypothetical scenario is slightly exaggerating screwybrewers hypothetical scenario.

Consider 3.6 °F error (2 °C) at 150 °F (65.6 °C) that's
100*2/(65.6 + 273.15) = 0.6% error. The pH scale is logarithmic. 10^0.02 = 1.047 ~ 4.7% error. But the actual numbers are moot. A pH error of a couple of tenths is enough to make a noticeable difference in your beer as is a 4 °F temperature error. Thus the validity of the analogy.

Personally I'd use expired buffers if they were stored properly.

I would too and do.

But looking at his post I see it says ±0.02. I'm sure it said 0.2 when I responded. I don't think I would have responded the way I did if it said ±0.02 because in that case I would have been exaggerating. Either I read what he posted wrong or he left out the extra 0 and went back and edited it in. Have no idea which at this point.

 

[Rjppunk]

I work as an environmental scientist performing groundwater sampling across the east coast for about 80% of my work year. I'm running a YSI 556 MPS meter as I'm posting this. The flow thru cell for the meter sees thousands of gallons a year, and I perform about 100+ calibrations and equal number of cal checks every year.

The brand my company uses is Oakton. The average 3 point calibration returns 7.00, 4.01, and 10.03 (on 7/4.01/10.00 solutions). The end of the day drift is +/- 0.02 after pumping 20-40 gallons across the probe head. The solutions and probes are checked monthly and replaced roughly ever 2 months from the parent container, which has a manufacturers use by date of 2 years usually.

Solutions will last a long time if you clean the probe head of residues, and rinse with dionized or distilled water from the grocery store, and wipe dry with a paper towel.

 

[adam01]

So I bought Hach ph buffer pillows - 4/7 +- .02.

I compared the 4.01 solution with my prior solution from Atlas - Wow! There was a .20
difference for 4.01 between them after calibrating the meter.

So I bought 2 packets of Hanna ph buffers to compare the 3. Here is what I found.

I calibrated the meter with the Atlas 7.0 and Hach 4.0 (I ran out of the Atlas). But didn't wait
enough for the meter to warm up.
This is a Milwaukee MW-101 and a Tek DMM ( K type) for temps.

Atlas read 6.90-6.91 at a temp of 22.0-22.5 C
Hach read 3.92-3.94 at a temp of 22.0-22.4 C
read 6.72-6.74 at a temp of 21.7-22.6 C
Hanna read 3.87-3.88 at a temp of 21.8-22.1 C
read 5.85-5.86 at a temp of 21.9-22.1 C

Between measurements, I blotted the probes on a paper towel.
Since this is beer science, the time between readings was homebrew time.

At the end, I adjusted the meter to the Hach readings (4.01/7.0) and reread the buffers
Hanna was high at 7.14 and low at 3.93.

I had hoped for closer correlation. I'll try again to see if I contaminated the solutions.

 

[user 141939]

Are you rinsing with DI between reads? Those numbers kind of suck. I was more accurate checking my crappy $7 pH meter against one at work. Also if you calibrated at 7.00 at it read 6.90 after cal, I would've done it again.



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[revansCAAD8]

I recently bought and started using Hach Buffer Powder Pillows. Is it okay to use them with Distilled vs. Deionized Water? I can't seem to find Deionized locally; checked 3 grocery stores, Walgreens, and at CVS.
In the past using Milwaukee Calibration Buffer Solutions and Bru'NWater I was always been close to projected PH. However my last brewday using the new Hach pillows (calibrated w/ Distilled) my mash was pretty off (actually started off close but kept creeping higher results).

Thoughts?

Thanks,
Robert
GypsyBrew

 

[ajdelange]

See what it says on the jug. I found that the distilled water I once bought at a drugstore was actually RO water. Even if the water is distilled there is the question of how many times it was distilled. Singly distilled water may not be that pure and, if distilled in glass, will contain some silicates.

Broadly speaking it is OK to use 'purified' water with buffer chemistry as the chemistry is designed to set the pH to the indicated value whatever you mix it with. That's what a buffer does but there are limits. The buffer has a certain 'buffering strength' and so does the water you mix it with. You want water with 0 buffer strength i.e. 18 MΩ purified water for absolutely best results but RO water with a couple of mg/L TDS will do.