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Thermal Desorption

Thermal desorption GC/MS is a type of dynamic headspace analysis which allows for the collection of volatiles from materials heated in the range of 50 to 400 C. The collected volatiles are then transferred to the GC/MS for separation and analysis. The capability to handle large samples and the absence of solvents permits very low detection limits and little interference in the analysis of contaminants, residual solvents, monomers, additives, and decomposition products.

The analysis is done using a Tekmar Model 5000 Thermal Desorber attached through a cryofocusing trap to a Hewlett-Packard GC/MS. The desorber sample oven is 5/8" by 7" and can handle substantial amounts of material. The cryotraps are capable of operation only to -150 C and while highly volatile materials (BP < -10 C) are not trapped with great efficiency, solvents as volatile as methylene chloride are quantitatively trapped.

APPLICATIONS

RESIDUAL VOLATILES IN PRODUCTS
Thermal desorption at moderate temperatures above the Tg or Tm can release solvents retained from raw materials or introduced during processing, shipping, or storage. Typical detection levels for a solvent such as methylene chloride is in the parts-per-billion range. Sample types include pharmaceutical tablets, medical disposables, implant materials, and food and beverage packaging. In addition, the technique can be used to trace contamination sources upstream from contaminated products.
THERMAL DECOMPOSITION VOLATILES
The thermal decomposition inlet system we use has the capability to hold samples at up to 405 C in inert atmospheres and then analyze the volatiles generated. This has applications in the understanding of decomposition mechanisms of high temperature composite materials as well as other polymeric systems. Stepwise heating and analysis of a single specimen can provide a provile of the volatiles from a given sample. Exposure of food containers, especially those used for the final heating of packaged foolds, to final use temperatures followed by analysis of the volatiles, can provide critical information on evolution of trace volatiles or thermal decomposition products.
ODOR ANALYSIS
Thermal decomposition GC/MS of food packaging has been successful in identifying off-odor components in packaging material as well as in the original polymer pellets. With special arrangements a "sniffer port" can be added to the gas chromatograph, and a representative from the client firm can be present during analysis to signal regions of interest.
OFF-SITE SAMPLING
The thermal desorption inlet system has the capability to desorb volatiles adsorbed onto special sampling tubes. These tubes are purchased by the client and used to sample air space using a vacuum pump. The tubes are sent to Micro-Scan Services in airtight shipping containers and then analyzed by TD-GC/MS. One use of this technique is in monitoring "sick building syndrome" volatiles in workspace environments, but it can be used in any situation where volatile organics may be causing process/product problems.
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