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[ Thermal Desorption | Index] Zoom: [PDF icon Printable PDF]
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Pages in this section: C6 C7 C8 C9 C10 C11
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C9
AutoDesorb
™
Scientific Instrument Services, Inc.
™
FAX: 908-806-6631
www.sisweb.com/catalog/08/C9
T
he desorption tube is then injected into the GC injection
port. The desorption tube will pass through the opening in
the middle plate of the Desorption Unit base to position
the desorption tube in proper alignment with the GC injection port
and the normally open desorption block assembly (7).
When injection is complete, a programmable time delay permits
the injection port pressure to equilibrate and the system is checked
for pressure leaks (8). If leaks are detected, the sample is
unloaded, the error reported and the next sample in the sequence
is analyzed.
If there are no leaks detected, the desorption blocks close
around the desorption tube and the desorption tube will ballistically
heat up to the set temperature or the temperature program ramp for
the heater blocks will begin (9). The combination of the heat applied
and the carrier gas flow through the Desorption Tube will purge the
desired components into the GC injection port and onto the front of
the GC column.
Normally desorption temperatures between 70°C and 250°C
are suitable for most applications. The maximum desorption tem-
perature permissible with the system is 450°C.
The heater blocks can be temperature programmed at ramp
rates up to 100 degrees/min. Multi-step and hold time desorption
heater block programs can be set up via the AutoDesorb software.
Normal desorption times vary from 3 minutes to 15 minutes, how-
ever longer desorption times up to 100 minutes are permitted. This
allows the trapped samples to be heated by the Desorption Tube
Heater Blocks, the analytes thermally desorbed from the adsorbent
resin and injected directly into the injection port of the Gas
Chromatograph via the shortest path possible, i.e direct injection
into the GC much like a syringe.
Since the column is normally maintained at subambient tem-
peratures, the desorbed compounds of interest are trapped on the
front of the GC column in a narrow band utilizing GC oven cooling
or the optional GC Cryo-Trap
™
Accessory. Despite the long desorp-
tion times, the peaks eluted from the column are extremely sharp
and well resolved.
When the sample has been fully desorbed into the GC column,
the desorption blocks are opened (10), the sample is uninjected
from the GC injection port (11), the Cryo-Trap is heated to release
the analytes from the Cryo-Trap and the GC
is started by the
AutoDesorb system. The GC temperature programming is com-
menced to elute and separate the analytes into the desired compo-
nents. The purge gas remains on for 5.0 minutes to cool the des-
orption tube and then the sample is unloaded back into the
AutoDesorb carousel (12).
When the GC analysis is complete, the next sample of the
ChemStation
™
sequence is loaded, the GC and AutoDesorb system
parameters are reset and this next sample is analyzed.
Theory of Operation of the AutoDesorb System (cont.)
GLT Thermal desorption tube with threaded ends.
Cross section of thermal desorption tube
Loading of Desorption Tubes for sample analysis
Loading of the Thermal Desorption tubes into the AutoDesorb
Carousel
GLT Desorption Tube
Glass Lining
Silco Coated
Stainless Steel
Outer Shell
Silco Coated SS Desorption Tube
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