D1840_10
0 (0 Likes / 0 Dislikes)
The user may use alternative
procedure B if preferred.
For recommended techniques,
refer to practices E169.
Check carefully sections
on handling and cleaning
of cells and glassware,
instrument adjustments,
and method of
absorbance measurement.
Prepare three dilutions
of the sample as follows.
If the sample is more
volatile than isooctane,
add 10 to 15 milliliters
of spectroscopic isooctane
to a clean, dry,
glass-stoppered, 25-milliliter
volumetric flask.
Weight out approximately 1
gram of sample in the flask.
Dilute to volume with
spectroscopic solvent
and mix thoroughly.
If the sample is less
volatile than isooctane,
weigh out approximately 1
gram of sample in the flask.
Dilute to volume with
spectroscopic solvent
and mix thoroughly.
Pipette 5 milliliters
of the first dilution
into a 50-milliliter
glass-stoppered volumetric
flask.
Dilute to volume with
spectroscopic isooctane
and mix thoroughly.
Dilute 5 milliliters
of the second dilution
to 50 milliliters in the same
manner as section 10.2.2.
Measure and record
the absorbance
of the spectroscopic
isooctane-filled sample cell
as compared to the spectroscopic
isooctane-filled solvent cell.
Transfer portions of the final
dilution into the sample cell
of the spectrophotometer.
Cover the cells immediately
to prevent transfer
of aromatic hydrocarbons
from the sample cell
to the solvent cell.
Check the windows of
the absorption cells
and make certain they are clean.
Measure the absorbance as
recommended in practices E169.
Record the absorbance
of the sample as
compared to spectroscopic
isooctane at 285 nanometers.
The dilution of
the sample should
be controlled so that
absorbance readings fall
within a range of 0.2 to 0.8
for maximum reproducibility
of results.
To accomplish this, it
may be necessary to use
an alternative third dilution
than the one specified
in section 10.2.3,
such as 10 milliliters
of the second dilution to
25 milliliters with solvent.