User`s guide

Theory of Thermal Desorption

314

Single-Stage versus Two-Stage

Desorption

Single Stage (Non-PerkinElmer)

If the volatiles extracted from the sample by thermal desorption are

swept directly onto the analytical column of the GC, the process is

known as single-stage desorption.

Figure 93 Single-Stage Desorption

Although this sounds like a simple and effective procedure,

single-stage desorption produces such broad component bands that

packed column chromatography is compromised and capillary

columns cannot be used at all. This limitation is overcome by

refocusing the desorbed volatiles on a secondary adsorption/

desorption stage before they are transferred to the gas

chromatograph.

Refocusing is conventionally carried out using one of the following

two procedures:

1. Cryofocusing on capillary tubing

2. Trapping the volatiles on a packed cold trap. This is the

method used in the TD and the ATD.

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