7 Reference
7.3 Ion measurement
186
HORIBA
7.3
Ion measurement
●
Ion concentration measurement
When certain ions exist within the solution that is to be
measured, the responsive ION electrode membrane
generates an electric potential corresponding to the
concentration of the ions. The potential that is generated
is measured by the ION meter, using the reference
electrode as the standard. With ION electrodes, the
measured potential and the logarithm of the ION activity
within the solution being measured are generally
proportional to each other and are expressed in the
following way:
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 concentration using an ION
electrode.
The part of 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 E
0
, finding the potential
E of the ION electrode inside the solution being
measured will enable the ION concentration to be
determined.
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Страница 11: ...CONTENTS VIII HORIBA ...
Страница 31: ...1 Overview of the Meter 1 9 Using the protective cap D 53 54 55 20 HORIBA ...
Страница 75: ...2 Taking Measurements 2 9 Dissolved oxygen DO measurement D 55 64 HORIBA ...
Страница 139: ...4 RS 232C communications 4 5 Communication example using the HyperTerminal 128 HORIBA ...