YOKOGAWA PH72, Руководство пользователя

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IM 12B03D02-01E
9-8
9 . Technical Information
pH0
pH14
pH7, 0mV
+mV
-mV
Second
calibration point
Theoretical line
First
calibration point
Calibration line (slope)
Asymmetry potential
F0910.ai
Figure 9.10 Calibration at Second Point
9.8 ORP (Oxidation-Reduction Potential)
In general, oxidation is the gain of oxygen or the loss of hydrogen, and reduction is
the loss of oxygen or the gain of hydrogen. In the electrochemistry field, oxidation
is defined as the loss of electrons and reduction is defined as the gain of electrons.
These reactions are reversible and expressed as follows:
Ox + n e Red
-
where Ox is the oxidized form of substance, Red is the reduced form of substance,
e – is an electron, and n is the number of electrons transferred. If an inert electrode
(not react with substances in a solution or not corroded by a solution, e.g., platinum or
gold) is immersed in a solution where oxidized and reduced forms of substances are
present, the electrode will acquire the potential that corresponds the ratio of activities
of both forms of substances and reaches its equilibrium. This potential is called the
oxidation-reduction potential (ORP). The ORP, E in millivolts, between the indicator
electrode and the reference electrode is expressed from the Nernst equation as
follows.
E : oxidation-reduction potential when potential of
standard hydrogen electrode* is 0
E : standard electrode potential when [Ox] = [Red]
R : gas constant
F : Faraday constant
n : number of electrons
T : absolute temperature
[Ox] : activity of oxidized form of substance
[Red] : activity of reduced form of substance
E = E + ln
R T
n F
[Ox]
[Red]
*
°
°
Standard Hydrogen Electrode (SHE)
Where:
(9.6)