horiba F-74BW, Инструкция по эксплуатации

Страница: 67 / 132

Chapter 3 Basic Operation
3.3 Calibration
F-74BW 55
4. Measurement of ion concentration
When a particular ion exist within the solution to be
measured, the responsive membrane of an ion electrode
generates an electric potential corresponding to the
concentrations of the ion. The generated potential can
be measured using an ion meter as the potential
difference from the reference electrode.
With ion electrodes, the measured potential is generally
proportional to logarithm of the ion activity in the
measured solution, and expressed in the following
formula.
E=E
0
+(2.303RT/nF)log
γ
C
E: Measured electric potential (V)
E
0
: Standard potential (V), determined according to
the system. This includes the standard potential of
the reference electrode and the liquid junction
potential.
F: Faraday constant (96,480 Cmol
-1
)
R: General gas constant (8.314 JK
-1
mol
-1
)
T: Absolute temperature (K)
n: Ion charge
γ
: Activity coefficient
C: Ion concentration (mol/L)
The above formula is called "Nernst’s equation" and is
the basis for measuring ion concentrations using an ion
electrode.
(2.303RT/nF), which is called the potential slope, incline,
slope, or Nernst's factor, is the change in potential
generated when the ion concentrations change by a
factor of 10. This change in potential is called the
potential slope, incline, slope, or Nernst's factor.
According to the equation, if you determine the values of
potential slope and E0 by calibrating the standard
solutions, you can obtain the concentrations of the target
ion by obtaining the potential difference, E of the ion
electrode inside the measured solution.
In actual measurement, an ion electrode measures the
ion concentrations, therefore, a linear relationship forms
between the logarithm of ion concentrations and the
electrode potential. Quantitative analysis using an ion