AutoDesorb
™
C8
Scientific Instrument Services, Inc.
™
Phone: 908-788-5550
www.sisweb.com/catalog/08/C8
Ready
Load Sample
Sample Loaded
Heat Blocks
Cool Cryo-Trap
Purge Gas ON
Injecting
Injection Complete
Desorbing Sample
Desorption Done
Sample Analysis
Unload Sample
T
he AutoDesorb System sits on top of the GC injec-
tion port of a Agilent Technologies 6890 or 5890
GC, where it is utilized for the direct thermal des-
orption of both volatile and semi-volatile samples into the GC
injection port and subsequently onto the GC column. It is
NOT permanently mounted to the GC. It is held in place by
gravity and can be lifted up and removed in seconds to
restore the GC to its normal operation. The only modification
to the GC is the addition of a carrier gas shut-off valve which
does not effect the normal operation of the GC. The GC can
be returned to normal GC operation in seconds.
The SIS
™
AutoDesorb system is controlled by a PC
Windows software program that is integrated with the Agilent
ChemStation
™
GC or GC/MS program to control the auto-
matic injection, timed desorption, multi-step temperature
ramp of heater blocks, control of GC Cryo-Trap accessory,
and remote starting of the GC and Mass Spectrometer (see
page C10). The Agilent ChemStation program is used for
sample information input and it controls the analysis of multi-
ple samples using the sequential running mode or single
samples using the normal run mode.
The standard desorption tubes are Glass Lined Stainless
Steel (GLT) Desorption Tubes which have an I.D of 3.0 mm,
are 4.0" long by 1/4" diameter and are threaded on both ends.
The inside of the desorption tube is lined with glass to provide
an inert environment for sample. In addition 4.0 mm I.D. tubes
are available in stainless steel and Silco coated stainless
steel. Samples to be analyzed are collected on the desorption
tubes containing an adsorbent resin such as Tenax
™
TA or
activated carbon. Alternatively, samples of small size (1 to
500 mg) can be packed directly into the desorption tube. The
ends of the tubes can be fitted with stainless steel caps with
seals to maintain sample integrity during sample storage. The
thermal desorption tubes can be reused hundreds of times
which brings the cost of sample containers down to pennies
per sample.
When ready for analysis, the thermal desorption tube is
attached to a connecting tube and the desorption needle is
attached to the other end of the desorption tube. This con-
necting tube is the adapter that enables the desorption tube
to be attached to the AutoDesorb carousel for thermal des-
orption analysis. The top of the connecting tube contains a
spring loaded sealing ball to seal the desorption tube and
maintain sample integrity until the actual thermal desorption
process begins.
The thermal desorption tube is then loaded into the
AutoDesorb system carousel. Up to 12 desorption tubes can
be loaded into the carousel (1). Tubes can be continuously
loaded and unloaded during the running of the sample
sequence. During the thermal desorption process, each des-
orption tube is checked for leaks. If a problem occurs with the
sample such as a pressure leak or system parameter prob-
lem, the sample is unloaded and and a report of the error is
indicated in the sample log table. The sample integrity is
maintained, which enables the error to be corrected and the
sample re-analyzed.
After the sample tube and connecting tube have been
placed onto the carousel, the Agilent ChemStation software
is set up with the GC or GC/MS method and the desorption
method is setup on the AutoDesorb windows. When the sam-
ple run is initialized on the ChemStation Window, the desorp-
tion tube is automatically loaded in the pickup mechanism (2
& 3). The desorption heater blocks are preheated to their ini-
tial temperature (4) and the cryo-trap cooled to its preset tem-
perature (5). The carrier gas through the desorption tube is
turned on and the flow can be manually adjusted via the flow
controller to between 1.0 ml/min and 120 ml/min for an initial
purge time (6).
AutoDesorb Sequential Operations
Theory of Operation of the AutoDesorb System
Desorption
T
u
be
Needle
Sealing
Ball
Connecting
T
u
be
Desorption
T
u
be
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