NAVI D-25, Инструкция по эксплуатации

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7 Reference
7.1 pH measurement
174 HORIBA
7.1
pH measurement
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pH measurement and temperature
The temperature of the solution being inspected is an
important parameter in the accurate measurement of
pH. There are many possible sources of errors during
measurement, such as the state of the solution junction
potential, asymmetric potential, and reference solution
pH concentration, but all of these items contain factors
that change with temperature. The best way to minimize
these potential causes of errors is to keep the
temperature of the pH standard solution uniform at the
time of calibration.
●
Liquid junction potential
Liquid junction potential is the electric potential that
occurs to a greater or lesser degree at the liquid
junction. The size of the electric potential differs
depending on the type of solution, the temperature of the
solution, and the structure of the liquid junction.
When solutions of different compositions come in
contact, ION diffusion occurs on the contact surface
between the two solutions. The ions are of various sizes,
so a difference occurs in the diffusion transfer speed.
As diffusion proceeds, a difference in charges occurs on
the contact surface of the two solutions, giving rise to a
difference in potential. This potential works to reduce the
transfer speed of fast ions and increase the speed of
slow ions, ultimately achieving a state of equilibrium
when the transfer speed of the positive and negative
ions on the contact surface of the two solutions is equal.
In this state of equilibrium, the potential at the contact
surface between the two solutions is called the
liquid
junction potential. A large liquid junction potential
means measurements will be very inaccurate.