IR sample preparation
for solid samples
What is a mull?
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a mull a suspension of solid sample in mineral
oil
It is used to make a thin-film cell from a solid
sample
Thin film IR cells
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Salt (NaCl) discs are used
To hold the sample
So the holder won’t absorb infrared light
and only sample absorption is detected
Sample preparation
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so dry the sample well
because water etches the IR discs
and emulsifies with oil letting less light through
How do I make a mull?
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grind
the sample
to a smooth
powder
add mineral oil
and mix it
well
What should the mull be like?
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the mull
should look
and spread
like soft butter
use clean gloves
to work with salt discs
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put on an extra pair
of gloves
to protect cells
from anything
aqueous on your
regular gloves
applying the mull
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use a rubber policeman
to spread
a thin layer
on one disc
lower the 2nd disc
on top of the 1st
and twist the discs
to spread sample evenly
placing discs in cell holder
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use your finger
to make a platform
in the cell holder
lower in
the NaCl discs
do not wedge them
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gently
place lid
on top
slide into position
in light beam
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close
sample
compartment
remove gloves
before using
keyboard
to clean discs
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add a few drops
of chloroform
to each disc
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rub gently
to clean off
all traces of sample
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…
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Keep discs dry
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replace
in desiccator
after cleaning
…