Hanna Instruments HI 4002 - Manual (Page 3)

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III. III. III. III. III. Theory of Operation Theory of Operation Theory of Operation Theory of Operation Theory of Operation:::::
The HI 4002 or HI 4102 Bromide electrodes are potentio-
metric devices used for the rapid determination of free Bro-
mide ions in food products, beverages, plants, soils and as
an indicator in titrations. The electrode functions as a sen-
sor or ionic conductor. The HI 4002 requires a separate
reference electrode to complete its electrolytic circuit. The
HI 4102 incorporates a reference electrode. The silver Bro-
mide pellet is practically insoluble in the test solutions
being measured and produces 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 bromide ions in solu-
tion 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 J/K Mol)
n= Charge on ion (1-)
A
i
=ion activity in sample
T= absolute temperature in K
F= Faraday constant (9.648 x 10 4 C/equivalent)