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Techniques & Tools Technology, Chemical, Gas Chromatography

Faster Chemical Separations

The Problem

Although gas chromatography (GC) offers chemical separation and identification, it can take a lot of time to perform the experiment and analyze the results when compared with real-time gas analyzers, which provide dynamic information about a process. Is it possible to combine the key benefits of both technologies?

Background

With efficient, soft ionization and high mass resolution, proton transfer reaction time-of-flight (PTR-TOF) analyzers have become the de-facto standard for real-time monitoring of trace volatile organic compounds (VOC). In a fraction of a second, a large spectrum of VOCs can be analyzed right down to parts per trillion (ppt) levels. Such high performance is ideal for monitoring complex samples in a variety of applications, including environmental monitoring, food and flavor research, life science applications, industrial process monitoring and many others. With a high-resolution TOF mass spectrometer, isobaric compounds can easily be identified by their difference in exact mass. However, isomers (compounds with the same chemical composition and consequently the same exact mass) are not separated in a TOF. Using GC pre-separation in combination with a PTR-TOF resolves this problem, but at the expense of real-time analysis, since a typical GC run takes around 30 minutes – more than a thousand times longer than a PTR-TOF analysis.

The run time of a GC begins at sample injection and finishes when the final compound elutes from the column, which depends on several factors – most importantly the column temperature. To speed up the process the column is heated (up to several hundred degrees), typically in an oven that represents the most significant contributor to the thermal mass of the system, which limits the speed of heating and also cooling. This is improved in fast-GC systems, which, in most approaches, reduce the thermal mass of the system (for example, by combining the column directly with a heating wire). Such systems reduce the runtime down to several minutes. A higher heating rate is usually achieved by applying more power – but a fast cooling rate is more difficult to accomplish. Of course, the cooling time sets a limit on when the next analysis can take place and therefore restricts the throughput.

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About the Author

Lukas Märk

CEO, IONICON Analytik GmbH, Innsbruck, Austria.

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