
7-11Needle-Type Environmental Sensors
7.4 Potentiometric Microsensors
Most ion-selective microsensors are potentiometric sensors where the voltage (mV generated vs. Ag/AgCl)
is th
eoretically
de
pendent
on th
e
lo
garithm
io
nic
ac
tivity,
acc
ording
to th
e
Ne
rnst
eq
uation
(E
quation
7.2)
:
E E E E E
cell external ref internal ref membrane junction
= − + +
. .
= + +
( )
( )
∆
E
RT
ZF
A
A
E
i
i
jref
external
internal
ln
ln
.
log
( ) ( )
= + =
′
+k
RT
ZF
A k
Z
C
i isample sample
0 059
(7.2)
where
E
cell
is the potential dierence between the ion-selective microsensor and the reference electrode
E
membrane
is the membrane potential
E
external ref.
and E
internal ref.
are potentials of the exter ...