Ph meter readings

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ForzaItalia

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Hi All

I have a bench top ph meter and recently noticed that the ph of my wine increases when i turn off my magnetic stirrer during testing the TA. Anyone know why this happens, is there something wrong with my ph meter? Is the ph of my wine more accurate when the wine is being stirred or static?

Thanks!
 
Does anyone know if this is normal? I am afraid that my meter is broken and have been messing up all my acid/meta additions. Thanks again.
 
I guess no one has encountered this problem so I guess I will just go buy a new PH meter...
 
Sorry you got no answers. Maybe if you gave a brand and model number it would be more likely to get a response from someone who has that model. At the very least I would contact the manufacturer about the problem since decent PH meters are not cheap! I know my PH meter reading continues to change, but there is an icon on the display that the instructions say when it disappears then hit the hold button because that is the real number right when that icon goes away.

BTW mine is a Milwaukee MW102. It doesn't have a stirrer, but a probe that senses temperature and corrects the reading for temperature automatically instead of my having to calculate adjustment myself. Nice feature.

Pam in cinti
 
Thanks for the response Pam! I have a Denver Instruments Basic PH Meter with ATC. I calibrated it with 4.01/7.01 solutions before testing the TA. I just found it odd that after I titrated the solution to 8.2 ph and shut off the stir plate the PH started going up over 8.2. Now I am just worried that all my acid additions are wrong!
 
Well, the better the mixing, the more accurate the number should be. One possibility is that you added the NaOH too fast, especially near the end and it wasn't completely mixed when you turned off the stirrer. So, the rise may have been coincidental. Once you reach the inflection point the pH will rise very rapidly with very little NaOH addition, so go very slow drop by drop and let it mix well between additions near the end of your titration.
 
Thanks Greg! I will try to test it again tonight and go very slowly this time. Hopefully that was the issue and I do not need a new PH meter.
 
I ask the following question out of ignorance. Might the magnets in the stir plate be affecting the electronics in your meter? Are they not usually powerful rare earth magnets? Might such magnets not play havoc with some mechanical or electronic components in your meter? What happens if you take a reading of the pH of the wine itself and then take a sample of the wine in the stir plate under the same conditions that you take readings for TA. Presumably if the pH changes when the stir plate is on then the problem may not be located in the meter nor in your titration technique but in the stir plate. If the meter remains constant then the problem is likely to be in your titration.
The other thing is - and I am not a chemist - I see that you calibrate your meter only below the 8.2 target. My meter comes with a pH 10 solution too. Might it not be worthwhile calibrating your meter at a higher level to make sure that there is no problem above 7?
 
No, the magnetic stirrer should not affect the electronics of the meter. However, IF you are stirring it in a plastic container, there may be a build up of static charge which could affect the meter. If that's the case, switch to a glass beaker.
 

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