pH Calibration Fluids, Storage Fluid, and Cleaning Fluid

[HDIr0n]

I was wondering if anybody could recommend some fluids for my pH meter.

I have found these sachets but couldn't find any reviews on them.

http://www.amazon.com/dp/B00DEPJEL4/?tag=skimlinks_replacement-20

I do kind of like the idea of sachets, and then I might get a 500ml bottle of the Storage fluid, and the Cleaning solution.

My meter that I just bought didn't come with any fluids so I need to get some fairly quickly. My meter is a 3 point calibration if that helps with the suggestions.

Thanks,
-Glenn

 

[ajdelange]

The one time use sachets are obviously very handy but they are expensive and as you need to calibrate at least each brew day (despite what the website you posted the link to says) and more frequently if you have an unstable meter use of them isn't really practical. Buy the buffers in Liter bottles or buy the capsules that you mix with 50 or 100 mL DI water before each use.

You will not be using your meter much above pH 7.0 unless you have water with high pH and want to check that or measure its P-alkalinity neither of which you really need to do. As a consequence of this you will not be doing 3 point calibrations.

The site lists the accuracy of these buffers as 0.002. This is BS. They are 0.02 buffers. AFAIK you can't buy 0.002 buffers but you can buy 0.01 at a premium.

You will definitely need the storage solution if your manufacturer calls for it but you can hold off on the cleaning solution. I have electrodes I have been using for years in brewing that have never required cleaning.

See https://www.homebrewtalk.com/f128/ph-meter-calibration-302256/ for tips on using pH meters.

 

[mabrungard]

+1 for AJ's comments. Purchasing the buffer capsules that are mixed with distilled water is a great way to reduce costs and improve the freshness of your calibration solutions. Those solutions should be replaced about every year or less, so it could get expensive quickly. Buying pre-made solutions in a bottle instead of sachet is certainly cheaper when you use the solutions frequently. One thing to recognize there is that you are paying a premium for those solutions since you are paying to ship water around the country. The capsules do reduce costs.

 

[fnord]

I've got some related questions if you guys don't mind.

I'm using the buffer capsules and mixing up 100 ml, then on brewdays pouring off 5 or 6 ml into vials to calibrate my meter. Are these solutions generally stable if stored with a tight lid? One post above sounds like they should be remixed every use and the other sounds like they are pretty stable. When I was getting low on the first batch I mixed up I checked against some of the satchels and was +/- .03, I know it isn't ideal but seeing that those satchels are +/- .02 I think it seems reasonable compared to the cost of mixing new buffers every time, but I also think I'm misinterpreting AJ's "before each use."

And the dumb questions how do you guys measure water on these? I have a 100 ml beaker, graduated syringe, graduated 100 ml jars, and a .1g scale. They all give me slightly different readings compared to weight, I go with the scale because I know it is accurate to it's calibration weight. Does it even matter too much if I am off but a couple ml? Something I read somewhere left me with the impression that they are solutions with high concentrations of weak acids and weak bases in proportion to buffer at the desired pH, and that it is the proportion that matters more than the concentration. I suspect I misread and my understanding is too simplistic.

 

[ajdelange]

I'm using the buffer capsules and mixing up 100 ml, then on brewdays pouring off 5 or 6 ml into vials to calibrate my meter. Are these solutions generally stable if stored with a tight lid?

Yes and even if the lid isn't too tight. pH 10 buffer is an exception. It takes up CO2 from the air pretty readily and should be stored tightly capped. The others, if not stored tightly capped, may lose a little water to the air but that doesn't have a major efferc.

One post above sounds like they should be remixed every use and the other sounds like they are pretty stable.

Ideally they should be mixed fresh using powder which is within its expiration date but if they are mixed fresh every week or so that should be plenty.

When I was getting low on the first batch I mixed up I checked against some of the satchels and was +/- .03, I know it isn't ideal but seeing that those satchels are +/- .02 [/QOTE]
Checked against what? If you have some old buffer and you mix new and calibrate the meter against the new then measure the old and the old is off by 0.03 then the old is somehow contaminated. Be sure when doing such tests that the meter is stable to better than 0.03 i.e. that if you recheck the buffer you calibrated with it should read the same as when you calibrated it. If your meter doesn't have ATC make sure the temperature of all the samples you are checking is the same as the temp. at which you did the cal. Also be sure you are doing the DI rinse and blot/shake routine between each measurement.

I think it seems reasonable compared to the cost of mixing new buffers every time, but I also think I'm misinterpreting AJ's "before each use."

By before each use I really intend each day on which you use the meter. Unless your stability check shows that more frequent calibration is necessary.

And the dumb questions how do you guys measure water on these? I have a 100 ml beaker, graduated syringe, graduated 100 ml jars, and a .1g scale. They all give me slightly different readings compared to weight, I go with the scale because I know it is accurate to it's calibration weight. Does it even matter too much if I am off but a couple ml? Something I read somewhere left me with the impression that they are solutions with high concentrations of weak acids and weak bases in proportion to buffer at the desired pH, and that it is the proportion that matters more than the concentration. I suspect I misread and my understanding is too simplistic.

No,that is essentially correct. Using ideally dilute solution chemistry the pH of the buffer is simply the pK of the acid base pair plus the log of the concentration ratio of the pair (i.e. if the acid and base are present at equal concentration the pH will be equal to the pK). But the world isn't ideally dilute and so if there is more or less water than the design proportion the pH of the buffer will shift slightly - the dilution effect. But as this is small you don't have to be terribly precise. You don't have to do the mixing in a volumetric flask in a water bath. I use a 50 or 100 mL mixing cylinders (a graduated cylinder with a ground glass stopper).

 

[HDIr0n]

Thanks everybody for your responses,

A.J. I have read over the primer you put together for pH meter use. And thankyou for putting that together.

I am wondering if anybody has used these brand of pH buffer tablets
Orbeco-Hellige RT561-0BT pH 7 Buffer Tablet
Link

The price looks good $15 for 100 tablets, now I just need to get a graduated cylinder and some wide mouth nalgene containers to store solution.

Thanks,
-Glenn