which brand pH calibration fluids to use? pinpoint = high variation

[CTaylor]

what do you all use to calibrate your pH monitors?
I found that different batches of pinpoint 10.00 fluid have pretty large variation between them. For instance, if I calibrate the monitor wiht one batch to 10.00, and then test the other batch, the monitor will read 9.70 (or along those lines). So, I thought it was due to one of them being an older batch. I got a third batch of 10.00 fluids and tested that. It came out with the same reading as the oldest batch. The middle batch is only a few months old. It's pretty pointless to calibrate with unreliable calibration fluids. I switched to milwaukee.. only because I know that pinpoint has excessive variation

What do you guys use? Do you even know that different batches of fluids can show very high variability? They do; at least pinpoint did in one of my batches (maybe more, but I cant remember).

[Crazy-Algae-Eater]

those liquids were made for you to caliberate your probe to read the correct PH depending what liquid you use not to test the liquid.

[Orochimaru]

Personally, a 0.3 is not a big deal. You have to consider the instrument error and the temp. differences between measurements. I calibrate mine with 8.00 buffer.

[gutterguppy]

Crazy-Algae-Eater

Could you explain further what you mean? I was always under the impression that a calibration solution provides a test sample at a known PH, so that the Meter can be calibrated to be accurate at that PH, thus helping to provide accuracy when testing a real sample. If a calibration solution is not truely at the PH its supposed to be, then wouldn't the meter calibrated in that solution also be off?

Logic would follow that if two bottles of the same standard differ by .3, then one or both bottles must not be accurate, which would throw off the meter if calibrated to that standard.

[Crazy-Algae-Eater]

yes, what i mean is that if the liquid says it 10.0 thne it is you need to calaberate the probe to read 10.0

[CTaylor]

yes gutterguppy, you are absolutely correct. that's the point of the problem in the first place. my batches of pinpoint 10.00 'calibration solution' show a great variation. IN other words, they are unusable. You cant calibrate something with a calibration fluid that is not reliable.

to the others.. 0.3 is way too much of a variation. might as well test with reagents and get much better accuracy if 0.3 was not a big deal. we buy our meters for accuracy, not best guesses.

crazy algae eater: yes, I know what calibration fluids are used for. if I didnt then I wouldnt have a problem with this. : )

thanx

[Orochimaru]

I guess how you perform the calibration will cut down the 0.03 variation, like 2 points curve is good and rinsing out your standard solutions with DI water between checks is good. You may want to try that first. Oh, and my mistake earlier I was thinking of 0.03 instead of 0.3. Yeah, 0.3 is a lot.