Thermal desorption is considered one of the most sensitive and environmental friendly sample introduction techniques for GC and GC/MS. Thermal desorption is used for the analysis of volatile organic compounds (VOCs) and semi-VOCs. Thermal desorption systems have been available for more than two decades and have shown few technical advancements in recent years, making them a relatively mature technology. However, new applications continue to grow the market, and new business agreements promise to further expand thermal desorption’s use worldwide.

A thermal desorption system is attached to the front end of a GC. A sample contained in a canister, on a sorbent media in a glass or metal tube, or a solid sample in a tube is heated and an inert gas flow carries the sample vapor to a capillary cryofocusing device or cold trap for concentration prior to GC analysis. Single-stage thermal desorption systems carry the sample directly to the GC without the concentration step.

Among the companies that develop and sell thermal desorption systems are CDS Analytical, DANI Instruments, Gerstel, Markes International and PerkinElmer. Although each manufacturer also sell tubes, Camsco and Sigma-Aldrich supply thermal desorption tubes for several manufacturers’ instrumentation. Earlier this year, OI Analytical began selling DANI’s Master TD 4750 Thermal Desorber in the US market. In February, Markets International signed a global OEM agreement with Agilent Technologies, which now offer Markes’ thermal desorption systems with the companies’ GC systems. The companies will also develop and promote thermal desorption applications. In November, Markes entered into an OEM agreement with Thermo Fisher Scientific.

One of the few companies dedicated to thermal desorption, Markes International was formed in 1997. It offers manual and automated thermal desorption systems, as well as accessories, consumables and software. Among the capabilities that make its thermal desorption systems unique is their backflush capability, according to Gavin Davies, Marketing Manager for Markes. Analytes concentrated on the cold trap are heated rapidly in a reverse flow of carrier gas. “On those systems, you won’t have an ice build up which causes the instrument to malfunction,” Dr. Davies told IBO. “You can get a larger range of analytes to be simultaneously analyzed than you could in a forward flush system.” The capability also allows for the simultaneous analysis of VOCs and semi-VOCs.

Sample recollection is another feature that distinguishes Markes’ systems, according to Dr. Davies. Markes’ SecureTD-Q technology enables quantitative recollection of split flow, allowing for re-analysis, as well as method or data validation. The company also offers the TT24-7 for continuous monitoring of gases, which Dr. Davis states is the only twin-trap system on the market. “When one trap is collecting sample from the air, the other is desorbing . . . [then] they switch over,” explained Dr. Davies.

The company’s newest thermal desorption system is the TD-100 system for sequential analysis of up to 100 sorbent tubes. “The TD-100 was brought out to be a simpler system to configure [and] easier for the customer to understand,” said Dr. Davies. An advanced version is pre-configured with automated sample recollection and electronic mass flow control split and desorption flows. Markes has also recently introduced a larger-capacity version of Micro-Chamber/Thermal Extractor for the simultaneous analyses of four samples of up to 114 mL each.

Materials emissions is the fastest-growing market for thermal desorption, according to Dr. Davies. He said the market is driven in part by regulations and in part by quality control in manufacturing and industry. Applications in this market include testing for emissions of VOCs and SVOCs from building materials, automobile components and paint. Among the legislation driving development of regulations are the EU’s Construction Products Directive, under which Germany’s Committee for Health-related Evaluation of Building Products has set VOC and SVOC emission limits for certification of flooring products. Thermal desorption is also specified as a testing method by the California Collaborative for High Performance School’s (CHPS) Section 01350 for indoor emissions of VOCs, which has been adopted by many building material manufacturers. CHPS is currently being updated, including the addition of more materials for testing. In order, from fastest to slowest growth, Dr. Davies cited environmental analysis, chemical warfare/forensic testing and food/flavor/fragrance testing as current applications for thermal desorption.

According to Gary Deger, director of Sales & Marketing for CDS Analytical, the primary changes in recent year for thermal desorption have not occurred in system design but in method development. “Over the last five years, there’s probably been more done on method development than product changes.” Method development has contributed to the expansion of applications for thermal desorption. He cited product emissions (materials emissions) and detection of chemical weapons agents as two of the fastest growing areas for thermal desorption system sales. One example of a product emissions application is the migration of plastics from food packing. “We can analyze the plastics or the food or compounds that migrated from the packaging into the food—trace [analysis] of plasticizers would be one thing, residual solvents or residual monomers, polysteryne, for instance,” he told IBO.

For detection of chemical weapons agents, the company’s products are utilized for fixed-point monitoring or in mobile vans. Detection limits for such applications can reach sub-parts per trillion levels. To improve the use of thermal desorbers for this application, Mr. Deger stated the need for battery-free systems. “Right now, thermal desorbers really need a power source,” he explained. Also to approve use with portable GC/MS systems, CDS Analytical is currently developing a smaller thermal desorption system. As for the environmental segment, which with thermal desorption is most associated, Mr. Deger stated that growth opportunities lie in developing countries. “Internationally, that environmental segment I would say is growing. In the US, I think it’s flat at best.”

CDS Analytical’s Dynatherm TDA-9300 autosampler allows for the use of sorbent tubes of any size from any manufacturer. “Traditionally, someone would design a method around a particular size tube and use that equipment. If you wanted to change equipment to a different vendor, the tubes were a little different and you might have to tweak the method a little bit,” explained Mr. Deger. “Our system allows them to use the old tubes in our system, so we can adjust it to take competitors’ tubes.” The TDA-9300 also offers thermal desorption and dynamic headspace in one autosampler. This feature, according to Mr. Deger, makes the system popular for emissions testing.

As for the future of the market, Mr. Deger suggests that publication of more ASTM methods based on thermal desorption would help grow the market. “There are some methods, but a lot of them are old and based around solvent extraction,” he told IBO. A relatively new standard is the German Automobile Producers Association’s Method 278 entitled “Thermal Desorption Analysis of Organic Emissions to Characterize Non-metallic Automobile Materials.” It specifies the use of thermal desorption for testing VOC and SVOC emissions from new car interiors. The Japan Automobile Manufacturers Association have instituted similar requirements.