NAVI D-25 Instruction Manual page 186

7 Reference
7.1 pH measurement
● Asymmetric potential
The glass electrode is immersed in a pH 7 reference
solution. When the electrode is immersed in the pH 7
solution, both the internal and external sides of the
electrode membrane are supposed to take on a pH of 7,
making the potential 0. In actuality, however, a potential
does occur. This potential is called "asymmetric
potential." The size of the asymmetric potential differs
depending on any stress that may have occurred during
the processing of the glass and the shape and
compositions of the glass. Asymmetric potential also
changes depending on the degree of contamination of
the reference solution and the state of the glass
membrane. Also, if the electrode membrane dries out, a
large asymmetric potential will occur, giving rise to
measurement errors.
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