D4928_12_12
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Prepare the apparatus for
use as described in section
10 of the written standard.
Ensure the syringe is
of suitable capacity.
See 7.3 of the written
standard and table 1.
Immediately after
the mixing step
described in 9.6 of
the written standard,
withdraw at least three
portions of the sample
and discard to waste.
Immediately withdraw
a fourth portion.
Wipe the needle clean.
Weigh the syringe and contents
to the nearest 0.1 milligram
and inject the test specimen
into the Karl Fischer reagent
below the surface of the
reagent in the titration cell.
Withdraw the syringe
and reweigh the syringe
to the nearest 0.1 milligram.
After the endpoint is
reached, record the result
from the instrument.
If the concentration
of water in the sample
is completely unknown,
it is advisable to start
with a small trial
portion of sample
to avoid excessive
titration time
and depletion of the reagents.
Further adjustment
of the aliquot size
can then be made as necessary.
Replace the reagents
periodically,
as described in 8.4 of
the written standard.
For crudes too viscous
to draw into a syringe,
add the sample to a
clean, dry dropper bottle
and weigh the bottle and crude.
Quickly transfer the
required amount of sample
to the titration cell
with the dropper.
Reweigh the bottle.
Titrate the sample as in
12.1.2 of the written standard.
When measuring the test
specimen by volume,
the measurement of the
volume is critical.
Special attention should be
used in determining the test
specimen volume.
Take care in filling
the syringe to reduce
the formation of gas bubbles.
The presence of gas
bubbles in a syringe
can be a source of interference.
The tendency of the
crude to form gas bubbles
may be a function of the crude
type and corresponding vapor
pressure.
Prepare the apparatus for
use as described in section
10 of the written standard.
Ensure the syringe is
of suitable capacity.
See 7.3 of the written standard.
Immediately after
the mixing step
described in 9.6 of
the written standard,
withdraw at least three
portions of the sample
and discard to waste.
Immediately withdraw
a fourth portion.
Wipe the needle clean,
invert the syringe,
and allow any bubbles in the
syringe to come to the outlet.
Expel the bubbles.
Wipe the needle and record
the volume in the syringe
to the nearest 1 or 10
microliters, as appropriate.
Inject the entire test
specimen into the Karl Fischer
reagent below the surface of the
reagent in the titration cell.
Inject the test specimen into
the Karl Fischer reagent.
After the endpoint is
reached, record the results
from the instrument.
Prior to reporting the
results, the results
shall be checked against the
repeatability requirement
as discussed in 16.1.1
of the written standard.