
59-11pH Measurement
Using an iridium/iridium oxide (Ir/IrO
2
) electrode as an example, this redox couple is believed to be
re
presented
b
y
a
n
I
r(III)/Ir(IV)
h
alf-cell
r
eaction
o
f
t
he
f
orm
2 IrO O O
2
+ + ↔ +
+ −
2H 2e Ir H
2 3 2
(59.11)
e Ir/IrO
2
electrode shows a near Nernstian response of −59 mV per pH unit [7]. e chemical resis-
tance,
hi
gh-temperature
an
d
pr
essure
pe
rformance,
th
e
no
nglass
co
nstruction,
an
d
th
e
co
nsiderable
po
tential
fo
r
mi
niaturization
su
ggest
th
at
th
ese
pH se
nsors
wi
ll
n
d
ap
plication
in ar
eas
no
t
ty
pically
em
ployed
b
y
g
lass
m
embrane
e
lectrodes
o
r
p
HFETs
.
59
.2.4.2
Li
quid Membrane Electrodes
Another
ty
pe
of el
ectrochemical
pH ...