D974_9 (14e2)
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Into an appropriate size irland
Erlenmeyer flask or a beaker,
introduce a weighed
quantity of the sample as
given in table one of
the written standard.
Add 100 milliliters
of the titration
solvent and 0.5 milliliters
of the indicator solution,
and without stoppering, swirl
it until the sample is entirely
dissolved by the solvent.
If the mixture assumes
a yellow-orange color,
proceed as directed in 9.2
of the written standard.
If it becomes green
or green-black
and base number
analysis is required,
proceed as directed in Section
10 of the written standard.
In routine analysis,
the indicator
may be pre-mixed with a
titration solvent before adding
to the sample.
Without delay, titrate at a
temperature below 30 degrees
Celsius.
Note 14 of the written standard.
Add 0.1 molar potassium
hydroxide solution
in increments, and mix
to disperse the potassium
hydroxide as necessary.
See Note 12 of the
written standard.
Shake vigorously
near the end point,
but avoid dissolving carbon
dioxide, CO2, in the solvent.
In the case of acidic
oils, the orange color
changes to a green
or green-brown
as the end point is approached.
When the solution first
turns green or green-brown,
reduce the increment
size to m manual buret,
or between 0.01 milliliters
and 0.05 milliliters, automated
buret.
Continue until a persistent
green or green-brown endpoint
is reached--
see Note 13 of the
written standard--
and held for a
minimum of 15 seconds
after the addition of
the last increment,
or if it reverses with two drops
of 0.1 molar hydrochloric acid.
When acid numbers about
or below 1 are expected,
better precision can be
obtained by substituting
0.01 molar, or 0.05 molar
solutions in 9.2 and 9.3
of the written standard.
This substitution was not
included in the development
of a precision statement.
To observe the endpoint
of dark-colored oil,
shake the flask vigorously
to produce momentarily
a slight foam when the
color change occurs
as the last few drops
of titrant are added,
and observe the titration
under a white fluorescent lamp
at benchtop level.
The temperature can be measured
by any suitable temperature
measuring device.
An automated photometric
device may also
be used to detect the
titration endpoint.
However, the precision
estimates given
in Section 15 of
the written standard
may not apply to this
mode of titration.
Perform a blank titration
on 100 milliliters
of the titration solvent,
and 0.5 millimeters
of the indicator solution,
adding 0.1 milliliter
or less increments of the
0.1 molar potassium hydroxide
solution.
The titration solvent usually
contains weak acid impurities,
which react with the strongly
basic components of the sample.
To correct the base
number for the sample,
determine an acid number
blank upon the solvent.