Chapter: INJECTORS
Topic:
OPERATION OF THE THERMAL DESORBER
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EXAMPLE OF TIMEDEVENT
TABLE FOR CONTROL OF
AUTOMATED tNIECTtON
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The column is connected to the
injection valve inside the valve oven using a
1/16"
to
lI8"
adapter and
0.040" J.D.
stainless steel tubing
(1/16"
O.D.). This
ensures a uniform sample temperature while
en route
to
the column and eliminates any
possible cold spots.
EXAMPLE OF TEMPERATURE
PROGRAM FOR DESORPTION
The ignitor element may
be
set
to
6OO"C (a dull red glow) for the duration of
the run
in
order
to
avoid any possibility of
Fill flame-out should the sample have a
high moisture content. The ignitor element
can operate continuously at this high
temperature without affecting
its
normal life
expectancy.
Replacement desorber tubes may be
ordered directly from Sandfue Scientific
Ltd.
in
Mission, B.C.,
Canada
at phone
(604) 826-5355
(part
no.
S-91(0).
To operate the SRI model
8610
thermal
desorption unit, the following steps are required:
1. Place a cleandesorption
tube with
a glass wool
plug at one end on a scale of known accuracy. The
tare weight is obtained. This is done
by
either
weighing the clean, empty tube and recording the
weight, or
by
placing the
tube
on the weighing
platform and zeroing the balance.
2.
Load the sample into the desorption tube and
place the tube back on the balance. The gross or
sample weight is recorded. The actual sample weight
is obtained
by
subtracting the tare weight from the
gross weight. A sample of solid weighing between
0.1 and 1.0gmis recommended for best results.
It
is
preferable
to
usea small sample due
to
the moisture
that
average samples contain. A small sample is less
likely to interfere with the
AD
detector flame. A
larger sample
will
permit the user
to
attain lower
detection
limits,
but water content must
be
considered.
3. The
tube
containing the weighed sample is
plugged with glass wool to hold the sample inside
and the tube is inserted into the
3/8"
opening of the
Swagelok'" hardware comprising the desertion
tube
cover. The end of the plugged
tube
is slid
into
the
opening
with
the nut loosened. Once the
tube
has
been inserted, the nut is tightened
to
seal
the sample
in
the assembly.
4.
Verify that the injection valve is in the
"LOAD"
position. Insert the
sealed
desorption
tube
assembly
into the desorption chamber opening on
top
of the
chromatograph and quickly secure it in place by
tightening the Swagelok" nut at the opening.
Care
should
be
exercised when performing this step. as
the desorption chamber is typically maintained at
350
degrees C and a burn potential exists.
5.
Initiate the chromatogram either by keyboard or
foot switch.
6. As soon as the desorption
tube
assembly
has
been
secured into thedesorption chamber. the injection
valve is rotated to the "INIEcr" position. and the
sample
is
allowed to
flow
into the column, After the
sample
has
desorbed completely, the valve is
returned to the
"LOAD"
position. The tube may then
be removed from the desorption chamber and
cleaned. The contents of the tube should be removed
and discarded. Once the tube
has
been thoroughly
cleaned, it may be returned to service. If in doubt. a
blank run should be used to verify that the tube has
been cleaned adequately. Once the blank
chromatogram is acceptable, the tube may be re-used
fora subsequent sample.
Users may
make
theirown tubes
if
sodesired.
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