I’ve read pH storage solution is simply 100 ml 4.0 buffer solution + either 1 g or 10 g KCL depending on the source. I get conflicting information. Does anyone make their own storage solution? If so what’s your recipe?
Storage solution is cheap, I get 500 mL bottles from Hanna. It’s cheaper than the buffers volume for volume. I think buying ready made would be the way to go if it does involve buffers. But I thought it was just a saturated solution of some salt, maybe the KCl? I’m sure Martin will set us straight.
Straight vinegar. Done.
Seriously? I understood that it was meant to be more or less identical to the solution inside the bulb to the end of maintaining an equilibrium. And it ain’t vinegar in there.
EDIT
SDS. 8 pages tell ya nothin’. US_HI70300_GHS_USA_3.pdf - Google Drive
(Well it tells you pH is 5-7.)
Yeah.
Yeah. Typical SDS. If it’s vinegar, they wouldn’t want you to know that because they can charge a whole lot more for their super fancy Hanna name-brand vinegar.
Well, Dave, one thing I’ve come to realize is that you are one of the kings of homebrew hacks. Makes me pay serious attention.
I’m a king of nothing. I just try to pay attention to what matters, and not pay attention to what doesn’t matter. Or hell, you can refer to me as “Lord Idiot the Lazy” if you like. 
Well, Lord Idiot the Lazy it is then; hey, that’s LOL! For the more formal approach, or unnecessary approach as it may be, this
https://www.coleparmer.com/tech-article/ph-electrode-care
says storage solution is 4M KCl, but 4.0 buffer may be substituted if that’s unavailable. There’s the basis of BrewBama’s recipe, I guess.
I figure, KCl is salt, and vinegar is sort of like a salt, but just an uglier molecular formula of CH3COOH. And the pH is about right. Good enough for me. And I even dunk it into the mash at 150 F and the probe hasn’t died yet.
I don’t think the pH of vinegar is “about right” compared to pH 4.0 buffer solution. I use white vinegar at pH 2.50 as a rough indicator of whether I need to calibrate my pH meter. If it reads 2.50 on the nose I will skip calibration, if it reads much different I will do the calibration with 4.0 pH and 7.0 pH solutions. To me 2.50 and 4.0 are very different, not about the same.
Can anyone explain the intended function of the storage solution? I have it on good authority that a) it is intended to be identical to the reference solution within the bulb, which by implication is 4M KCl, maintaining a stable (I presume that means osmotically) condition, and that b) 4.0 buffer is a viable substitute. The two can’t possibly, as it appears to this layman, be consistent. Little help?
I use homemade vinegar at 3.9. So… YMMV.
As for why 4.0 buffer or KCl and the mechanisms involved… sorry, Robert, I don’t know why. It’s magic!?!
Rob, I just looked up the description for the Oakton pH electrode storage solution that the Grape sells. It says:
“4 oz bottle of Oakton pH electrode storage solution. Maintains a gel layer on the pH electrode bulb and minimizes clogging.”
I know that the solution contains Potassium chloride (KCl) since I get deposits of the salt on the outside of the vial that the electrode is stored in from evaporation. With all due respect to Dave (a.k.a. LOL ;D), I am not sure that I would want to store my electrode in a straight weak acid (your homemade vinegar, or plain 4.0 buffer for that matter), because I would be afraid of the acid contaminating the osmotic characteristics of the bulb, but that is me. A bottle of the Oakton stuff lasts me about a year and I feel the 13 bucks I spend on it gives me some piece of mind that I am following the manufacturer’s recommendations and thirteen bucks is a lot cheaper than a new electrode. That said, I am sure you might be able to find the storage solution cheaper online.
Goose, I looked up the MSDS for your storage solution. It says:
Component: Potassium Chloride
Weight: 20-30%
*The exact percentage (concentration) of composition has been withheld as a trade secret.
It also says the pH range is 6.3-6.9. So… who knows.
So it looks like the most generally preferred storage solution is in fact a saturated solution of potassium chloride, based on the various sources we’ve looked up. The Hanna SDS gives pH 5-7, and Goose’s is near 7. 4.0 buffer is sometimes recommended in a pinch. I wonder if your source suggesting combining KCl with 4.0 buffer was just conflating the two pieces of advice?
I still favor buying the cheap 500 mL bottle of storage solution. I only buy buffers in single use sachets, because once opened the shelf life is very short, far shorter than it would take me to use even the smallest bottle even if doing double duty, and once a portion has been used it can’t be reused for calibration; so I don’t see buying that in bulk for use in any way for storage purposes.
EDIT
Good ol’ Wikipedia and links have helped elucidate some of this. KCl is in fact the reference solution in the electrode. Makes sense to use it as the storage solution.
pH has little to do with storage solution. The osmotic strength and the ions are the important features and vinegar doesn’t even come close to cutting it. In most cases, pH probes employ a potassium chloride solution as the electrolyte and the purpose of storage solution is to replicate that environment on the exterior of the probe’s bulb to avoid drawing out the ionic content from the bulb. I’ve seen storage solution molarity vary between 1 and 4 and its dependent upon the probe manufacturer. In essence, the storage solution molarity is dependent upon the probe’s electrolyte molarity. So in a way, you should try and use the storage solution that the probe manufacturer recommends. If its a piece of crap probe, I wouldn’t be surprised to hear of a manufacturer recommending the use of tap water. For good probes, use real solution.
With all that said, there are several sources that suggest that STARTING with a 4 buffer solution is a decent idea since it has very little ionic content and the low pH isn’t a problem. The 4 buffer is also more stable than other higher pH buffers. From that starting point, add solid KCl to the buffer (or distilled water) to create a KCl solution of at least 2 molarity. For many probes, that should be close enough.
Thanks, Martin!
That’s what I’ve been waiting for. I echo the thanks Martin.
I too appreciate your presence and response Martin. Sincerely.
Now… if it ain’t broke… ;D ;D ;D ;D
By that logic then why not urine? It’s way cheaper, kind of salty (there is probably some KCl in there) and you don’t even need to take the cap off a bottle to get it. Now that’s what I call lazy mans electrode solution. 