pH Buffer Solution: Lifespan Once Opened?

[BrewDrinkRepeat]

pH meter newbie here.

Premade buffer solution is more economical and convenient than the single-use pouches you mix yourself, but I worry that I won't use it often enough to go through it before it expires.

About how long do they last once opened?

 

[mabrungard]

I'm confused with your contention. The pouches of powder that you add to distilled water will typically produce about 100 ml of solution. That will easily keep for 6 months, when capped in a suitable container.

Are you talking about the single-use, ready to use calibration solutions that are dispensed in ketchup-like packets? They would be less economical. But the dry powder versions that you have to mix up, are very economical.

 

[ajdelange]

Premade buffer solution is more economical and convenient than the single-use pouches you mix yourself, but I worry that I won't use it often enough to go through it before it expires.

There are the single use pouches that look like ketchup packs that are very convenient and indeed quite expensive but you don't mix anything - they are pre mixed. You may have these confused with the 'powder pillows' which is a little plastic pillow shaped thingy that you snip open and then pour the powder into 50 mL DI water. Then there is the bottled stuff. In order of cost per use per buffer (assuming 50 mL) looking at the Hach products:


Single use packet: $1.71
500 mL Bottle: $1.13
Pillow: $0.77
4L Jug: $0.628
20L Cubitainer: $0.377

So unless you buy the stuff 4L or 20L at a crack the pillows aren't that expensive and are less expensive than the half liter bottles. Obviously if you take less than 34 mL from the 500 mL bottle then it becomes less expensive than the pillow.

About how long do they last once opened?

That depends on the buffer. 7 buffer appears to expire about 2 years after opening whereas 4 buffer appears to be good for 4 years. I'm guessing this is because the 7 buffer will absorb CO2 from the air.

Now the powder pillows also have listed expiration dates but as the chemicals are in powdered form and hemetically sealed from the air until opened I tend to ignore those (unless I am working on something to be published).

 

[MagicMatt]

I take it he is talking about buying the buffers in bulk "pre-made" solution (i.e. the 500mL+ sized bottles). I bought a 1L bottle each of the 7.01 and 4.01 buffers, and a 500mL bottle each of the storage solution and cleaning solution.

To the OP, in hindsight I only brew about twice a month so this was probably overkill and now I'm pushing the limits for expiration (and still have about half a bottle of each left). If I had to do it again, I would opt for the smallest container that offered the most cost savings per mL. From AJ's post it looks like the powder pillows might be the way to go.

 

[BrewDrinkRepeat]

As I said, newbie here. I thought the small "pillows" were single-use, so there was my first error!

I was referring to the larger-volume liquid versions, and how long they would last. I normally brew once every 1 - 2 months (sadly that's about all I can fit in my weekend schedule, but I'm working on that!) so I worry about them expiring before I have a chance to use them all up.

If I go with the pillow packs, will any seal-able container be OK to store them?

Thanks all!

 

[ajdelange]

The pillows are cheap enough that they can be single use though I usually keep the solutions around until the next time I brew or use the meter for something else. The advantage of them is that you have fresh buffer each brew day.

 

[Brewski_59]

I was wondering myself, how long can I trust the powder buffers after they have been mixed? I store them in pint mason jars and only open the jar when I'm calibrating the sensor on brew day.

 

[ajdelange]

Once they are mixed they are pretty much the same as the liquid buffers though they might have less mold inhibitors or none at all. IOW the 7 buffer will absorb CO2 from the air and degrade faster than the 4 but should still be good for quite a long time. But the whole point of the pillows approach is that you mix fresh buffer each time you need some.

 

[BrewDrinkRepeat]

OK, so I ordered my Hach Pocket Pro+ yesterday, as well as my buffers. A buddy of mine recommended these buffer capsules so I went ahead and ordered a set (4, 7 and 10):

http://www.amazon.com/gp/product/B00BASN3YG/?tag=skimlinks_replacement-20

 

[ajdelange]

You'll probably never use the 10 unless using lime for softening but be aware that once mixed they pick up CO2 from the air faster than the other two so be sure to mix them fresh for each use.

 

[BrewDrinkRepeat]

That's exactly what I thought, that using the capsules I'd probably just mix up a fresh batch each time (unless I happen to be brewing two weekends in a row, perhaps). I generally brew less than once a month on average, and at $2.70 / batch to calibrate it seems like a very reasonable cost to me. Much more so than my stupid propane costs!

As for the 10, if I'm reading the manual correctly the Hach uses all three for calibration. Is that not right?

 

[mabrungard]

I use maybe 10ml of each solution for calibration, so my 100ml batch of each solution lasts something like 10 brew days. And as AJ points out, the typically used 4 and 7 solutions are fairly stable and store well in my capped bottles. You should be able to get much more use than one.

Unless you were going to measure in the range above 7, there is no need or desire to calibrate a meter with the 10 solution. Use only the 4 and 7 solutions for typical brewery use.

 

[BrewDrinkRepeat]

These are the containers I bought to mix up the buffers, hopefully I can store them in these as well:

The Hach manual seems to indicate that it needs all three for auto-calibration, but I can do a manual 2-point calibration using 4 and 7 and be OK? Will doing all three (since I bought all three) make it any better?

Calibration points: Pocket Pro: 3 points (auto); Pocket Pro+: 3 points (auto) or 2 points (custom) Note: Temperature calibration is not available.

Auto-recognition calibration standards: USA: 4.01, 7.00, 10.01 pH; NIST: 4.01, 6.86, 9.18 pH

 

[mabrungard]

The Hach manual seems to indicate that it needs all three for auto-calibration, but I can do a manual 2-point calibration using 4 and 7 and be OK? Will doing all three (since I bought all three) make it any better?

That is an AJ question, since he has that meter. Most meters employ a 2-point calibration to set the slope and offset. Unless you are measuring in the 7+ range, it seems pointless to calibrate there.

 

[ajdelange]

The Hach manual seems to indicate that it needs all three for auto-calibration, but I can do a manual 2-point calibration using 4 and 7 and be OK?

It does two point calibrations automatically as well as three. You start the cal procedure by putting it in a buffer and getting a reading which you decide when to accept (a great feature of this meter) it then tells you to put it in a second buffer and after you accept the second reading you have the option of terminating the calibration or going into the third.

Will doing all three (since I bought all three) make it any better?

No. It uses the 3 buffer measurements to construct a two piece linear calibration curve with the break at the 7 buffer. You only need the three point calibration if you are going to measure both above and below 7 in a particular session.

 

[BrewDrinkRepeat]

Gotcha. As always, thanks guys for all the great info! Extremely helpful to guys like me (with no science background).

Followup Q: I intend to calibrate before each brew session. It's OK for that to be the night before (when I'm doing other prep work like milling grains, etc.)? Or should I calibrate right before I take my first measurement from the mash?

 

[mabrungard]

In my opinion, you should turn on the instrument a good 15 minutes beforehand, so that it can warm up and stabilize. Then check calibration just prior to your brew day begins. Checking the day before seems unnecessarily risky.

 

[ajdelange]

Followup Q: I intend to calibrate before each brew session. It's OK for that to be the night before (when I'm doing other prep work like milling grains, etc.)?

We hope you will check out https://www.homebrewtalk.com/showthread.php?t=302256 and do the stability test described there. Whether or not you feel you can calibrate the night before or not will depend on the results of the stability test and how much error tolerance you have.

Or should I calibrate right before I take my first measurement from the mash?

That's always going to be the most conservative approach and that's what I do on brew days but I'll admit that when I'm checking pH in the fermenter next day to see if the yeast are doing well I often do not recalibrate (but I know the electrodes are stable for a couple of days - not stable enough for brewing but stable enough to check that pH is falling).

As for warmup - these things don't have valves in them any more. If you leave a modern meter on for 15 minutes to warm up then it will probably turn itself off automatically. The only thing that's left to drift in a way that would make a difference in a modern meter is the A/D converter and the instrumentation amp that drives it. Those will be temperature compensated. Any error due to temperature drift that the compensation of the electronics (this is not ATC) doesn't take out will be taken up in the calibration. Any that occurs between calibration and the calibration check will be detected in the calibration check. I do, however, think it is a good idea to let the thing 'warm up' for a minute or 2, not that I've ever done that intentionally. It usually happens automatically as you go off to fetch something you forgot, answer the telephone...