<1. General Information>
1-3
IM 12Y18A03-01EN
1st Edition : Oct. 04, 2019-00
Figure 1.1 WE430 Schematic
The oxygen scavenger present in the sample reacts with the iodine to form iodide ion:
OS
red
+ X • I
2
→ 2X • I
-
+ OS
ox
Where:
OS
red
= oxygen scavenger reduced
OS
ox
= oxygen scavenger oxidized
The iodide sensing electrode responds logarithmically to changes in the resulting iodide ion
concentration. This response is described by the Nernst equation:
E = E
o
+ 2.3 (RT/nF) log (C/C
iso
)
Where:
E = measured electrode potential, mV
E
o
= potential, when C equals C
iso
, mV
R = ideal gas constant
T = temperature of sample, degrees K
n = valence of ionic species (-1 for iodide ion)
F = Faraday’s constant
C = effective iodide concentration (activity)
C
iso
= concentration (activity) of iodide ion where potential E is temperature independent
(isopotential point)
E
0
default: 44 mV
Low limit of E
0
: - 50 mV
High limit of E
0
: + 150 mV
Slope default: - 64.0 mV/decade
Slope range: - 75.0 mV/decade to - 40.0 mV/decade