
59-6 Chemical Variables
59.2.1.2 Glass Membrane Indicator Electrode Response to pH
When
th
e
me
mbrane
gl
ass
is im
mersed
in aq
ueous
so
lution,
a ge
l-like
hy
drated
la
yer
on th
e
or
der
of
10
0
nm th
ick
fo
rms
at th
e
su
rface
of th
e
gl
ass
. Wit
hin
th
is
hy
drated
la
yer,
th
e
ex
change
of so
dium
io
ns
in th
e
gl
ass
fo
r
hy
drogen
io
ns
in th
e
so
lution
pr
oduces
a po
tential
di
erence
be
tween
th
e
hy
drated
la
yer
an
d
th
e
so
lution
th
at
de
pends
on th
e
hy
drogen
io
n
ac
tivity
. e ne
t
po
tential
de
veloped
ac
ross
th
e
en
tire
glass membrane, ϕ
net
, is the sum of boundary potentials ϕ
b
, at the inner (reference element side) and
ou
ter
(
sample
si
de)
e
xtents
o
f
t
he
m
embrane:
φ φ φ