[KellerBrauer]

Greetings fellow brewers.  I have had the same three bottles of pH testing solution (4.1, 7.0 & Storage) for several years.  Well, as ignorant as this may sound, I just noticed that each of these three bottles has an expiration date!  My understanding is that the pH of a substance does not change unless forced to do so.  How can these solutions expire?  Could this simply be a marketing tactic?

[braufessor]

I would think once they are open they can be compromised over time due to Carbon Dioxide, etc.  I do not know the practical significance of the changes though in regard to just how much of a difference it could make in practice/operation.  I am sure someone will have more precise information than I will.

I went to these years ago for convenience and peace of mind....
https://www.testequipmentdepot.com/milwaukee/accessories/calibration-solutions-and-reagents/solutions/ph-4-buffer-solution-m10004b.htm

[Robert]

Unopened, they should be good until the expiration date.

Once opened, contact with atmospheric CO2 will cause them to go south fairly quickly.  The general rule is that pH 4.0 and 7.0 solutions are good for an absolute maximum of 6 months, but depending on conditions possibly not nearly that long.  pH 10.0 solution deteriorates much faster.

And it should go without saying that once you have dipped a probe into a quantity of solution,  it is compromised and must be discarded.  Don't just dip in the bottle, pour out what you need for a single use.

I would never buy a bottle.  Just get the single use sachets.  They look more expensive at first.  But when you take into account that they are sure to be in perfect condition every time you calibrate, whereas you'll never be sure of your results after the first use from a bottle, and that you'll end up dumping most of a bottle when it goes bad a few months after you buy it, they make sense.

Cleaning and storage solutions are not subject to the same problems.   Cleaning solution is basically just hydrochloric acid, and storage is a saturated potassium chloride solution, so they  keep just fine.  Buy the biggest bargain bottle you can.

[dmtaylor]

I will ask my Chemistry friends at work.....

[goose]

Yes they will deteriorate over time as Rob mentioned.  The stuff I buy is from a laboratory supply house  and the bottle has an expiration date of one year.  That said the 4.0 and 7.0 solutions should not degrade that much until the expiration date is reach especially if unopened.  Two years or more, I would probably throw them out.

Although the sachets are better, I use all of my bottles up before the expiration date and the differences in viability are probably small enough that it won't make that much difference in a homebrewing environment.  In a lab environment, things are a bit more critical.  RDWHAHB

Hint:  Swirl the probe in a small amount of 7.0 before calibrating and then swirl it in a small amount of 4.0 before doing the second calibration.  Throw these rinsing solutions away and use fresh solutions for calibrating steps.   Don't just stuff the probe in the second solution or rinse it with water between solutions steps.

[Black Lion Homebrewery]

Like others have stated they degrade quickly.  Hannah has calibration buffers in small pouches.  I'd recommend those instead for intermittent testing. 

[dmtaylor]

I will ask my Chemistry friends at work.....

I asked my buddy:

"I know pH calibration solutions (like '4.01' or whichever) have expiration dates on them.  However, in your personal experience, how long do you believe they might last on the shelf in REAL life?"

His response:

"As you probably figured – it depends on several variables.  First is the storage area temperature – if the storage temperature is above 75°F, the buffers will decompose much quicker.  Second, if the buffers are stored in a dark area versus bright lighting – bright lights and especially higher UV light spectrums will break down the buffer molecular structure.  Third, the type of buffer – pH 4.00, pH 7.00, or pH 10.00 – the higher the pH buffer value, the more likely atmospheric carbon dioxide (acidic) will degrade (neutralize) the buffer.  Last, the type of container they are stored in – glass, polycarbonate, or plastic – the best is glass since there is less chemical interaction with the buffer.

Our own procedural shelf life (based on ASTM guidelines) is 13 months or 1 year from opening the container.  The 'real' shelf life, if purchased with a freshly manufactured solution in a dark glass bottle stored in a dark room at 50°F, would probably be 3-4 years with pH value within ±0.02 s.u. of the stated value."

[Slowbrew]

Great info Dave!

That means my bottles are at best only 2 years out of date.   

Paul

[dmtaylor]

Great info Dave!

That means my bottles are at best only 2 years out of date.   

And mine are simply due for replacement right now.  I had a feeling it was about time.... the timing just feels right. 

[narvin]

The 'real' shelf life, if purchased with a freshly manufactured solution in a dark glass bottle stored in a dark room at 50°F, would probably be 3-4 years with pH value within ±0.02 s.u. of the stated value."

Good to know.  I have some almost empty bottles that are about 4 years old but were stored well. I might see what they measure when I calibratw with new solution.

[dmtaylor]

The 'real' shelf life, if purchased with a freshly manufactured solution in a dark glass bottle stored in a dark room at 50°F, would probably be 3-4 years with pH value within ±0.02 s.u. of the stated value."

Good to know.  I have some almost empty bottles that are about 4 years old but were stored well. I might see what they measure when I calibratw with new solution.

THAT is the best idea, and exactly what I too had in mind for when I get my new solutions -- compare side by side, then we'll know for sure!

[goose]

I will ask my Chemistry friends at work.....

I asked my buddy:

"I know pH calibration solutions (like '4.01' or whichever) have expiration dates on them.  However, in your personal experience, how long do you believe they might last on the shelf in REAL life?"

His response:

"As you probably figured – it depends on several variables.  First is the storage area temperature – if the storage temperature is above 75°F, the buffers will decompose much quicker.  Second, if the buffers are stored in a dark area versus bright lighting – bright lights and especially higher UV light spectrums will break down the buffer molecular structure.  Third, the type of buffer – pH 4.00, pH 7.00, or pH 10.00 – the higher the pH buffer value, the more likely atmospheric carbon dioxide (acidic) will degrade (neutralize) the buffer.  Last, the type of container they are stored in – glass, polycarbonate, or plastic – the best is glass since there is less chemical interaction with the buffer.

Our own procedural shelf life (based on ASTM guidelines) is 13 months or 1 year from opening the container.  The 'real' shelf life, if purchased with a freshly manufactured solution in a dark glass bottle stored in a dark room at 50°F, would probably be 3-4 years with pH value within ±0.02 s.u. of the stated value."

Thanks, Dave!  Mine are stored in their original plastic bottles in a dark place (a cupboard in my brewery) and the temp in that room never exceeds 75 degrees.  So I am OK.  That said, I still buy fresh buffer once a year since I use it up that fast and the 200 ml bottles are relatively cheap compared to the sachets.   Just a note, I calibrate my pH meter once a month.

[KellerBrauer]

This is great and helpful information.  Thank you all.  So I gather, light and atmosphere are the major culprits responsible for the degradation of the pH buffers.  So, it makes sense to buy the small sachets since they are typically light proof and if unopened can last for quite some time if kept below 50°.  So, perhaps I can buy those little guys in bulk and save a few bucks???  Worth looking into!!

FWIW - my solutions are edging on 2-3 years beyond their expiration!!  Oops! 

[dmtaylor]

I'm more concerned about the stability of the 7.01 or 6.86 solution than the 4.01 since it will absorb less CO2 over time.  I/we should think about replacing the 7.01 or 6.86 probably annually, but the 4.01 can last for several years.  That's what I'll focus on.  But I'll be replacing both of mine before next batch.  And testing the old against the new solutions to see how big a difference it really made.  I'll report results if I remember, and please, if you guys do this, please do the same!  Thanks!

[Craig Hairrell]

I'm regretting buying a pH meter that needs 4.0, 7.0, and 10.0 calibration solutions. They're not available in sachets, making ongoing use much more expensive.

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