Hanna Instruments HI 4109, Instruction Manual, Page: 3 / 16

3
III. III.
III. III. III. Theory of Operation
Theory of Operation
Theory of Operation Theory of Operation Theory of Operation:::::
The HI 4009 or HI 4109 Cyanide electrodes are potentio-
metric devices used for the rapid determination of free Cya-
nide ions in effluent, for electroplating bath analysis and
as a detector for titration of cyanide with silver nitrate
.
The electrode functions as a sensor or ionic conductor. The
HI 4009 requires a separate reference electrode to complete
its electrolytic circuit. The HI 4109 incorporates a reference
electrode. The silver halide 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 Cya-
nide 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)