pH Meter Calibration Solution: How long is it good for?

[jholen]

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

 

[samc]

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.

 

[DSmith]

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?

 

[wildwest450]

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.

 

[ajdelange]

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).

 

[Hermit]

Does refrigeration/freezing affect the shelf life of these buffers?

 

[ajdelange]

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.

 

[jholen]

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)

 

[ajdelange]

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.

 

[mabrungard]

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!

 

[ajdelange]

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).

Actually, they are calibrated over a reasonable range of temperatures and the pH values at each of those temperatures are listed on the packaging in some cases and in others they are not. But as they are standardized NIST buffers the pH values are stored in the meters and so it is possible to do as you suggest.

But (there is always a but) as we all know pH meter calibration uses two buffers to determine two parameters, the slope and offset, of the electrode. There is actually a third, the isoelectric pH which is assumed in every meter I have ever seen to be 7. If it is not 7 ATC doesn't function as it should. Error is fairly insensitive to pHi so that it is actually specified as 6.5 < pHi <7 and as long as it is in that range the error introduced is small. But it can approach the basic buffer accuracy of ±0.02 pH and you want the buffers, not the meter/electrode, to be the limiting factor. Thus I always recommend that buffers and sample be within a few degrees of one another.

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?

You'd have to know the pK's as a function of temperature and anyway a theoretical calculation isn't what is desired here. These are technical (secondary) standards and are compared to the primary standards that actually define the pH scale. It's by comparison to those that the data are obtained. Anyway, it has been done for you already.

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

I think this is a case where it is best to follow manufacturers recommendations. Just looking at a bottle of 4.01 buffer with an expiration date of 5/14 (and I know I've had it over a year) that says expiry date is valid for storage between 10 and 25 °C. So putting that in the fridge would not be a good idea. Don't know why but I'll take them at their word.

 

[kraypd]

AJ: I was just listening to your water workshop MP3 for my second time. I heard you mention the importance of using fresh buffers so I decided to order new bottles.

I discovered that the ones I brought one year ago were already past their prime and it has been affecting my pH calibration / readings. This explained some of the confusion I was running into between the spreadsheets / measurements that I have been facing for the past few brews.

I know that you have heard this many times but thanks a great deal of your work and effort in educating the rest of us. I, for one, have benefited a lot from your postings/site.

 

[cjones586]

Its been a while since I worked in a lab - but we used to buy our pH meter calibrants in powder form and make them up fresh in DI water immediately before use. We'd buy a box of sealed foil sachets of each calibrant, which I would guess should last a very long time - if not forever. You can get them from one of the big chemical companies, like Sigma-Aldrich

e.g.
http://www.cannonwater.net/ph_buffer_variety_pack.aspx

 

[revansCAAD8]

I'm about to order new buffer solutions and was thinking about these from Hach (50ml) pillows:

http://www.hach.com/buffer-powder-pillows-ph-4-01-nist-color-coded-red-pk-50/product?id=7640204347

http://www.hach.com/buffer-powder-p...olor-coded-yellow-pk-50/product?id=7640205050

OR these (but more expensive - 20ml) tablets:

http://www.coleparmer.com/Product/pH_Calibration_Buffer_tablets_4_0_50_bag/SC-55200-00

http://www.coleparmer.com/Product/p...NWZ2JRdvi-fG1hJvt18NHBrz2aNZONy5OsaAiX98P8HAQ

Any experience with these? Leaning towads the Hach but very expensive shipping too but can't seem to find other vendors with cheaper shipping and/or in stock. I would think the 100ml pHydrion tablets are too much volume for a brewday use? I usually only brew once a month so would likely need to make fresh each brewday.

Thanks for any help,
Robert
GypsyBrew

 

[sandyeggoxj]

I bought my calibration solutions in 20ml sachets with expiration dates. The were about $1 each including shipping. Some are made by Milwaukee and some are Hanna. They look like they came from the same factory. . I have a mw102 meter fwiw.

 

[ajdelange]

I use the Hach pillows as a matter of course. I have also used the pHydrion capsules but not recently as it is easiest for me to order from Hach. I actually find the 100 mL volume from the pHydrion a bit more convenient to work with than the 50 mL from the Hach and feel a little more secure with that volume as whatever contamination gets carried over on the electrode (be it just DI water or anything else) has half the effect on 100 mL that it does on 50). I have never used the tablets.

 

[revansCAAD8]

Thanks all. Not really interested in sachets, our 230ml bottles of buffers lasted us nearly a whole year. I like the idea of mixing up exact amounts of fresh buffers (pillows/tablets) each brewday. AJ, do you work for Hach? I have never ordered from them before.

Robert
GypsyBrew
-using a mw101 meter

 

[ajdelange]

No but I have bought a lot of their gear over the years.

 

[CyclingCraig]

I'm about to order new buffer solutions and was thinking about these from Hach (50ml) pillows:

http://www.hach.com/buffer-powder-pillows-ph-4-01-nist-color-coded-red-pk-50/product?id=7640204347

http://www.hach.com/buffer-powder-p...olor-coded-yellow-pk-50/product?id=7640205050

Any experience with these? Leaning towads the Hach but very expensive shipping too but can't seem to find other vendors with cheaper shipping and/or in stock. GypsyBrew

I purchased the Hach ones and they work great for me. Easy to mix up before brewday (I do it the night before).

Split the order with a friend that has a pH meter .. that is what I did, 50 tests is A LOT.. 25 is more reasonable for me to use up in 2 years.

Also I would suggesting picking up a few of these:
Sample container
I prepare my 4 and 7 in them, then use another for the sample that I am measuring.

Just a side note. I brewed over the weekend, So I made fresh calibration solution and calibrated my meter (MW-102). I had some left over pH 4.01 buffer from 5 weeks ago in a storage container and decided to see what it was reading... 4.02!! So I would think if you mix them up and are carful with you calibration and not contaminating them, they should be good for at least a month or so.

-Craig

 

[Rjppunk]

At the consulting firm I work for, we keep parent bottles of cal solutions and fill up calibration containers. The containers are good for up to 3 months depending on how well the YSI probes are cleaned before calibrating. Once the solution is suspect we check the pHmV of the unit, and compare the old with a new solution, and toss it if its questionable. We then rinse the container, dry, and refill from the parent bottle (until it is nearing the expiration date). Ours see a lot of use so you may get more time from yours.

 

[revansCAAD8]

I purchased the Hach ones and they work great for me. Easy to mix up before brewday (I do it the night before).

Split the order with a friend that has a pH meter .. that is what I did, 50 tests is A LOT.. 25 is more reasonable for me to use up in 2 years.

Also I would suggesting picking up a few of these:
Sample container
I prepare my 4 and 7 in them, then use another for the sample that I am measuring.

Just a side note. I brewed over the weekend, So I made fresh calibration solution and calibrated my meter (MW-102). I had some left over pH 4.01 buffer from 5 weeks ago in a storage container and decided to see what it was reading... 4.02!! So I would think if you mix them up and are carful with you calibration and not contaminating them, they should be good for at least a month or so.

-Craig

Thanks so much! Did you order them direct from Hach?
PS. on those sample containers; I was afraid they would be to light and top heavy which could fall over with our wired MW probes? I have been using slight over-sized shot glasses for my buffers/DI but they don't have a lid.

 

[CyclingCraig]

Thanks so much! Did you order them direct from Hach?
PS. on those sample containers; I was afraid they would be to light and top heavy which could fall over with our wired MW probes? I have been using slight over-sized shot glasses for my buffers/DI but they don't have a lid.

Yes, I ordered directly from HACH. Pretty fast service, and money well spent on quality stuff from them.

Those containers ARE pretty light, and will get knocked over easy with the probes in them. but if you are carful or hold them while the calibration process runs it's not too bad, the calibration only takes a minute or two. But they work our GREAT for storing the buffers for use on future brews.

-Craig

 

[ajdelange]

There are various tricks that can be used the simplest of which is to see which way the container plus electrode wants to tip and then simply putting something behind it in that direction. Far and away the best solution is something like this: http://static.coleparmer.com/large_images/5500000.jpg

 

[revansCAAD8]

Thx again guys. Anyone know of any Hach discount codes by chance? Trying to keep the boss lady from killing me ;-)

 

[ajdelange]

Once the solution is suspect we check the pHmV of the unit, and compare the old with a new solution, and toss it if its questionable.

It took me a while to figure out what this means and I finally concluded that it means that the meter is put into mV mode and comparative mV readings are taken of fresh and old buffer. Most people here have meters that do not have mV modes. There is really no need to use mV mode to do the comparison. pH mode is fine. If the old buffer reads more than 0.01 or 0.02 different from the new then toss it and use the new. But then while it does make sense to do this in a situation where you have cubitainers of buffer and dozens of meters it really does not in the home brewing context. Let's say you find the old buffer is still good. What do you do with it? You've already prepared or drawn a fresh buffer sample. Might as well use it. Seems simpler to just prepare/draw new buffer each time we brew. This would be a good technique for getting a handle on the real storage life of your buffers, though. Each time you order a new bottle/pack of pillows you do the comparison to see how well the old stuff has stood up to time.

 

[BrewKnurd]

Last night i tested out some buffer solutions which I'd opened somewhere between 1-2 years age. I calibrated my meter with the old solutions, then checked to see what it read on a freshly made buffer. The fresh 7.0 buffer settled out at 7.09. So, in this particular case, with storage at temps ranging from probably 50-70 (the buffers were sitting out in my storage room off my garage, so there's a window AC to limit how hot it gets but its free to get as cool as the weather dictates in the winter), the old 7.0 buffer looks to have been about 0.1 units low after a year or two.

 

[ajdelange]

I did a comparison between an old buffer at end of 3 yr (I think it was) life and a brand new, freshly opened bottle and found the difference to be less than ±0.02 pH i.e. less than the label tolerance of the pH.

 

[PlexVector]

I just now became concerned with my calibration buffers which are approaching 2 years. Thinking of going with the Hach singlets which are about $35 for pack of 20; however that would be for each pH standard. So, if I do a two point calibration I could go with 4 and 7 I guess.

But more to the point I contacted Hach through their chat interface and the shelf life of the 7pH buffer specifically was stated as 2 years.

The pic is a clipping from the Hach application note from the web site. Rather than put a link, which will eventually break I thought this would be better. In my case I have a 500mL bottles of buffer and about 2 years old, so for me I should have never bought that large of quantity.