NAVI F-52, Instruction Manual

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Chapter 16 Reference
16.3 Ion measurement
F-52, 53, 54, 55 225
The above formula is called “Nernst’s equation” and is the basis for measuring ion concentra-
tion using an ion electrode.
The part of the above Nernst's equation that reads “2.303 RT/nF” is the change in potential
generated when the ion concentration changes by a factor of 10. This change in potential is
called the potential slope, incline, slope, or Nernst's factor. If the above equation is adhered to
when calibrating with standard solution and determining the value of the potential slope and
E0, finding the potential E of the ion electrode inside the solution being measured will enable
the ion concentration to be determined.
When actual measurement is performed, the ion electrode measures the ion concentration, so
a linear relationship forms between the value of the ion concentration and the electrode poten-
tial, if the concentration is plotted on a logarithmic axis, as shown in Fig.2. Conducting quan-
titative analysis using an ion electrode requires either an ion meter that has an antilog
calculation function or the creation of a calibration curve using similog graph paper.
Fig.2 Relationship between ion concentration and electric potential
Potential slope
Calibration curve for univalent positive ion electrode
Po
tentia
l (mV)
Ion concentration (mg/L)