AutoDesorb™ (Catalog C7)

C7

AutoDesorb™

FAX: 908-806-6631

www.sisweb.com

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

injection port of a Agilent Technologies 7890, 6890

or 5890 GC, where it is utilized for the direct ther-

mal desorption 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

automatic 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 standard desorption tubes are reusable Silco Coated

Stainless Steel 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. Samples to be ana-

lyzed 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.

When ready for analysis, the thermal desorption tube is

attached to a connecting tube and the desorption needle is

attached. This connecting tube is the adapter that enables the

desorption tube to be attached to the AutoDesorb carousel for

thermal desorption 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.

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 sample run is initialized on

the ChemStation Window, the desorption tube is

automatically loaded in the pickup mechanism (2 & 3). The

desorption heater blocks are preheated to their initial

temperature (4) and the cryo-trap cooled to its preset

temperature (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).

The desorption tube is then injected into the GC injection

port.(7 & 8) If there are no leaks detected, the desorption

blocks close around the desorption tube and the desorption

tube will ballistically heat up

(or temperature ramp) 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.

Normal desorption times vary from 3 minutes to 15

minutes. The analytes are 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.

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 desorption 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 commenced to elute and

separate the analytes into the desired components. The

purge gas remains on for 5.0 minutes to cool the desorption

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.

AutoDesorb Sequential Operations

Theory of Operation of the AutoDesorb System

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