pH buffer pillows
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I assume you are referring to pH calibration solutions, for which I may have some insight.
The pH calibration solutions I frequently use at work last about 4-8 months after having been opened. I would suspect that oxidation and precipitation of the buffer compounds may be the causes of degrading quality.
The easy way to find out would be to mix up and store a calibration solution for a few months and compare it to a freshly mixed solution to see how big the deviation is.
The pH calibration solutions I frequently use at work last about 4-8 months after having been opened. I would suspect that oxidation and precipitation of the buffer compounds may be the causes of degrading quality.
The easy way to find out would be to mix up and store a calibration solution for a few months and compare it to a freshly mixed solution to see how big the deviation is.
The buffers are probably potassium bipthallate and a mixture of mono and dibasic phosphates respectively as those are the popular formulas for technical buffers. They should be stable as can be but I note that the expiration dates on the pillows themselves isn't very impressive though the powder is clearly sealed away from air in the pillow.
The following things might effect the pH of a long-term stored buffer:
1) Pickup of carbon dioxide from the air is going to pull the 7 buffer towards a lower pH. It is the nature of a buffer to resist this (that's what buffers do) but in so doing the buffering capacity is somewhat reduced.
2) Pseudomonnas sp. bacteria can apparently eat pthallic acid
3) Evaporation will cause the buffer to become stronger and there is a small but finite shift in pH associated with this
4) The buffer will become diluted because the electrode was not completely dried before being inserted into the buffer container and because some electrode fill will enter the jar as well
5) The buffer will become contaminated with other things that the electrode has measured (wort, the other buffer...)
I can't get through a box of pillows before they expire and wind up throwing some away. It is so little trouble to mix up new buffers that I do it every time I brew and every day when I am working in the lab.
The following things might effect the pH of a long-term stored buffer:
1) Pickup of carbon dioxide from the air is going to pull the 7 buffer towards a lower pH. It is the nature of a buffer to resist this (that's what buffers do) but in so doing the buffering capacity is somewhat reduced.
2) Pseudomonnas sp. bacteria can apparently eat pthallic acid
3) Evaporation will cause the buffer to become stronger and there is a small but finite shift in pH associated with this
4) The buffer will become diluted because the electrode was not completely dried before being inserted into the buffer container and because some electrode fill will enter the jar as well
5) The buffer will become contaminated with other things that the electrode has measured (wort, the other buffer...)
I can't get through a box of pillows before they expire and wind up throwing some away. It is so little trouble to mix up new buffers that I do it every time I brew and every day when I am working in the lab.
