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Old 02-01-2012, 02:55 AM   #1
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Default pH Meter Calibration Solution: How long is it good for?

Just received my Hanna pHep 5 today, along with storage solution and my calibration solutions (4 & 7). My meter is soaking in the storage solution as per the maintenance instructions in the manual. I then intend to calibrate it to verify it in proper working order, then add storage solution to the cap and store it upright. Anyways, on to my question... on the bottles it states that it needs to be replaced after 3 months.

Is this typically the case that everyone else has seen? If so, is there a more economical way to go about storing/using the solutions (even though I got the double pack from MoreBeer! I think that the supply they gave me would last far longer, quantity wise, than three months - I understand the quality of the solution will degrade).

Thanks,
- J

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Old 02-01-2012, 04:47 AM   #2
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No idea how long it lasts, but I hesitate to buy repackaged solutions for unknown handling issues. I prefer the one time capsules or packets of pre-made solution.

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Old 02-01-2012, 01:09 PM   #3
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I'm very interested in this topic too because I have narrowed my choice down to that same Hanna meter and was planning on getting the 230ml bottles of calibration, storage & cleaning solution with the initial purchase. The calibration solution bottles may not be worth while vs the packets if I plan to use the device about once a month if they expire within 6 months.

What expiration date is on the storage & cleaning solutions?

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Old 02-01-2012, 01:22 PM   #4
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Quote:
Originally Posted by jholen View Post
J My meter is soaking in the storage solution as per the maintenance instructions in the manual. I then intend to calibrate it to verify it in proper working order, then add storage solution to the cap and store it upright.
It's best if you calibrate it on brew day, they don't hold calibration. At least not for a long time.
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Old 02-01-2012, 02:13 PM   #5
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The most important things WRT pH meters are
1. Store the electrode properly
2. Calibrate before each use (that means each day - not before each measurement on that day.
3. Use fresh buffers (the capsules whose content are added to DI water just before use are, IMO, best but note that they have a finite shelf life too)
4. Try to have buffers and samples at as close to one another in temperature as is possible (a few degrees).

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Old 02-01-2012, 02:38 PM   #6
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Does refrigeration/freezing affect the shelf life of these buffers?

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Old 02-01-2012, 02:47 PM   #7
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Lowering the temperature slows chemical reactions so I'd say yes. However I can't see freezing as being good for them. I really have no idea as to how the shelf lives are arrived at i.e. I don't know whether it's the lab or the marketing people who have more influence. The buffers are potassium pthalate and mixtures of phosphate salts. Those are pretty stable compounds AFAIK. In the form I like, they are sealed in airtight packages so I don't imagine that's an issue. I know I am throwing useable stuff out when I honor expiration dates and I'm sure that if getting mash pH right were the only concerns I'm sure I'd be fine using them beyond their expiration dates. Within reason, of course. I just found some capsules in a drawer that have been there 20 years. They are going in the trash.

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Old 02-01-2012, 03:28 PM   #8
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Lowering the temperature slows chemical reactions so I'd say yes. However I can't see freezing as being good for them. I really have no idea as to how the shelf lives are arrived at i.e. I don't know whether it's the lab or the marketing people who have more influence. The buffers are potassium pthalate and mixtures of phosphate salts. Those are pretty stable compounds AFAIK. In the form I like, they are sealed in airtight packages so I don't imagine that's an issue. I know I am throwing useable stuff out when I honor expiration dates and I'm sure that if getting mash pH right were the only concerns I'm sure I'd be fine using them beyond their expiration dates. Within reason, of course. I just found some capsules in a drawer that have been there 20 years. They are going in the trash.
Thanks for the tips.

I'll be putting my buffer solution in my beer fridge, then just take it out and let it warm up to room temp before using.

Curious AJ, where do you get your capsules that you add to DI water?

Edit: These them? http://cynmar.com/ProductDetail/11334124_Hydrion-Buffer-Capsules-Ph40-10vial (and then the 7.0)
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Old 02-01-2012, 04:45 PM   #9
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Quote:
Originally Posted by jholen View Post
Curious AJ, where do you get your capsules that you add to DI water?

Edit: These them? http://cynmar.com/ProductDetail/11334124_Hydrion-Buffer-Capsules-Ph40-10vial (and then the 7.0)
No, but I used to use them (the old ones I found were from that manufacturer). I note with interest that their website says they keep indefinitely. The ones I use come from Hach (who made my meters) and they do have expiry dates even though they are better sealed than the pHydrion ones. I'm not recommending the Hach over the pHydrion. In fact the pHydrion make 100 mL of solution whereas the Hach only make 50. The Hach ones are the same tolerance ( ± 0.02 pH) as the others and are labeled as being NIST traceable. The Cynmar site doesn't specifically mention that but they still may be.
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Old 02-01-2012, 05:04 PM   #10
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Buffer refrigeration. Interesting thought.

With temperature compensation, would it be possible to calibrate a pH meter at the refrigerated buffer temperature and then use the calibrated instrument at a more normal room temperature (say 25C)? I'm not sure that the electronics would properly compensate since buffer solutions are calibrated to a certain pH at a certain reference temperature (say 20C or 25C).

I'm assuming that the pK's of the buffers could be used to back calculate what the buffer pH should be at the refrigerated buffer temperature? That's probably a pain in the tail, so it would probably be best to just take the buffers out of the fridge a day ahead of time.

I do like the thought that refrigeration could extend buffer life though!

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