3
III.
III.
III.
III.
III. Theory of Operation
Theory of Operation
Theory of Operation
Theory of Operation
Theory of Operation:::::
The HI 4011 or HI 4111 Iodide electrodes are potentiomet-
ric devices used for the rapid determination of free Iodide
ions in food products, plants, and as an indicator in titra-
tions. The electrode functions as a sensor or ionic conductor.
The HI 4011 requires a separate reference electrode to com-
plete its electrolytic circuit. The HI 4111 incorporates a
reference electrode. The Silver Iodide pellet is practically
insoluble in the test solutions being measured and pro-
duces a potential change due to changes in the sample
’
s
ion activity. When the ionic strength of the sample is fixed
by the addition of ISA, the voltage is proportional to the
concentration of iodide ions in solution and the electrode
follows the Nernst equation.
E= E
a
+ 2.3 RT/nF log A
ion
E= observed potential
E
a
= Reference and fixed internal voltages
R= gas constant (8.314 volt coulomb/K Mole)
n= Charge on ion (1-)
A
i
=ion activity in sample
T= absolute temperature in K
F= Faraday constant (9.648 x 10
4
coulomb/mole)
