How frequently should one calibrate a PH meter. Of course I calibrate it every time I take it out of the box to use it. But should it be calibrated during use?
Maybe once an hour? or after every different wine sample? or between every titration where I do several titrations on the same sample?
Thanks Ray
Ray, it depends on the meter and the probe. I have an old, old Orion model
601 meter and an inexpensive plastic probe. This combination needs calibration every time I turn the meter on. If I leave the meter on for a week, the calibration does not shift. You can determine how often your meter needs calibration by measuring the 4.01 buffer solution every hour or so. lumRay, To add to Lums comment, you could also add a post calibration at the end of use for the day to see where things ended up once you are reasonably confident the meter behaves well in normal circumstances.
The meter is usually not the issue, it's the probe. As they degrade they either get very slow to respond or 'drifty'. This is a normal consequence, so just because it worked great last year does not mean this year it will behave the same. Winemaking seems to be kind to the electrodes I'm using, I had a very inexpensive meter I used for 5 years, (a Hanna pHep3) that worked well the entire time. The pHep5 I use now is 2 or 3 year old and both have never had probe problems. I doubt you will need to re-calibrate during a sessions, but checking never hurts.
I always calibrate before use, but I have inexpensive models and you have to do that with them; besides, it's good practice anyway. That way you have some assurance the readings are worth something. I'm not sure I ever saw a lab tech use a pH meter without calibrating the system before use; it's just not worth the risk. (My backround is measurement science, we are really anal about getting the measurement as right as you can so I'm always suspicious of where I can get it wrong too...)
It sounds like you are on the right track since you always calibrate before use, so I hope this helps. By the way, a buffer needs replacement every so often, mold growth is one thing to use as an indicator the buffer is losing it. Regards, Joe
Thanks Lum and Joe.
I am using a Phep5 from Hanna. The first time I used it, it seemed to drift about .2 over an hour or so. The second time I checked it several times during the session and it did not seem to drift enough to worry about. But thought I would ask. I do like the instrument and for the first time I trust my titrations of my red wines.
Joe, in your comment on the buffer going bad, are you reffereint to the callibration samples or to the NaHO used in titration? The calibration samples I am using come in sealed packets such that one sample is in a packet. That should be safe I would assume.
Ray
Ray,
I was talking about the calibration 'buffers'; since yours are fresh it's not an issue.
Opened buffers can last 2 to 3 months as long as you keep them tighly sealed.
I use Hydrion Capsules to make up the buffers, you can get them from any lab supply house. They are really economical and more than accurate enough for your meter, (I have the same one).
Mine was one of the brand new pHep 5's and has a bug in the firmware; when it shuts off it forgets the calibration. It's a little annoying, but I hear they fixed it in later versions. It forces me to recalibrate so I really don't care.
It's normal for the probe to drift a bit when new; I usually let them sit in a buffer of 3 or 4 for a few hours to let them stabilize when new.
Joe
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