Chemistry Reference
In-Depth Information
3
Probes for pH measurement and
simultaneous cellulose removal and bleaching
of textiles with enzymes
P. WESTBROEK AND P. KIEKENS
3.1
Introduction
This chapter examines various probes for pH measurement such as ion-
selective and glass-membrane electrodes as well as simultaneous cellulose
removal and bleaching of textiles with enzymes.
3.2
Ion-selective electrodes
3.2.1
What is an ion-selective electrode?
Ion-selective electrodes belong to the group of potentiometric methods.
Many electrode systems, partly well known, partly in development and
under investigation, show a Nernstian relationship between the measured
electrode potential and the activity of a species in solution. Important con-
ditions to be fulfilled for the development of ion-selective electrodes are
the affinity of a membrane surface for a typical ion or molecule and a
minimum ion conductivity over the membrane. If possible, but not neces-
sarily, these conditions should be fulfilled at room temperature.
In practice (Fig. 3.1), the potential difference, D
E
,is measured over a
membrane:
D
EE E
=-
2
[3.1]
1
where
E
2
is the actual potential of the interface solution 2 (membrane
surface 2), and
E
1
is the potential of the interface solution 1 (membrane
surface 1). This difference is related to the activity of a species in solution
according to the following equation:
D
E
=kR
T z
F
ln
a
[3.2]
i
i
being a variant of the Nernst equation (Equation 2.7), where k is a constant,
R is the gaseous constant,
T
is the temperature (K),
z
i
is the charge of the
species, F is the Faraday constant, and
a
i
is the activity of the species.
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