D7318_9
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Prepare the titrator by
filling the titrator reservoir
with lead titrant, 8.1
of the written standard.
Follow the
manufacturer's procedure
for filling the burette.
Perform titrations in
monotonic titration mode,
using either 25 microliter or
50 microliter titrant addition
increments.
Use a 10 millivolts per
minute drift condition,
or 20-second wait time
between additions--
whichever is achieved first.
Proper care of the lead
selective electrode
is essential for obtaining
high-quality titration curves.
Preparation of
the lead electrode
should be performed as
specified by the manufacturer.
A lead electrode utilizing
a solid crystal sensor
requires polishing when
performance deteriorates.
The voltage range for a 10 parts
per million sulfate in ethanol
titration should span
at least 50 millivolts
and produce an acceptably-shaped
titration curve.
See figure 1 of the
written standard.
If this level of electrode
performance is not met,
this indicates a need for
lead electrode polishing.
The lead electrode normally
comes supplied with a polishing
grit and a cloth rectangle.
The polishing grit medium
is placed on the cloth,
wet with ethanol or water,
moved over the surface
of the cloth for a
minute, rinsed with water
to remove the polishing medium,
and wiped dry with a tissue.
The electrode is then
soaked in lead titrant, 8.1
of the written standard,
to re-equilibriate
the electrode surface.
The double junction
reference electrode
is filled with 1
molar lithium chloride
in absolute ethanol, 8.7
of the written standard,
in the outer chamber.