Abstract
Abstract. We present a compact and versatile cryofocusing–thermodesorption unit, which we developed for quantitative analysis of halogenated trace gases in ambient air. Possible applications include aircraft-based in situ measurements, in situ monitoring and laboratory operation for the analysis of flask samples. Analytes are trapped on adsorptive material cooled by a Stirling cooler to low temperatures (e.g. −80 °C) and subsequently desorbed by rapid heating of the adsorptive material (e.g. +200 °C). The set-up involves neither the exchange of adsorption tubes nor any further condensation or refocusing steps. No moving parts are used that would require vacuum insulation. This allows for a simple and robust design. Reliable operation is ensured by the Stirling cooler, which neither contains a liquid refrigerant nor requires refilling a cryogen. At the same time, it allows for significantly lower adsorption temperatures compared to commonly used Peltier elements. We use gas chromatography – mass spectrometry (GC–MS) for separation and detection of the preconcentrated analytes after splitless injection. A substance boiling point range of approximately −80 to +150 °C and a substance mixing ratio range of less than 1 ppt (pmol mol−1) to more than 500 ppt in preconcentrated sample volumes of 0.1 to 10 L of ambient air is covered, depending on the application and its analytical demands. We present the instrumental design of the preconcentration unit and demonstrate capabilities and performance through the examination of analyte breakthrough during adsorption, repeatability of desorption and analyte residues in blank tests. Examples of application are taken from the analysis of flask samples collected at Mace Head Atmospheric Research Station in Ireland using our laboratory GC–MS instruments and by data obtained during a research flight with our in situ aircraft instrument GhOST-MS (Gas chromatograph for the Observation of Tracers – coupled with a Mass Spectrometer).
Highlights
Atmospheric trace gases introduced to or elevated in concentration in the environment by human activities often show adverse environmental impacts
To extend the substance range, we developed similar cryofocusing–thermodesorption units for our other gas chromatography – mass spectrometry (GC–MS) instruments (Hoker et al, 2015; Obersteiner et al, 2016), which are currently operated in the laboratory
We consider these results to be valid in principle for our other gas chromatograph (GC)–MS set-up discussed by Hoker et al (2015) and the GhOST-MS described by Sala et al (2014) as all preconcentration set-ups rely on the same principal set-up and similar components are used
Summary
Atmospheric trace gases introduced to or elevated in concentration in the environment by human activities often show adverse environmental impacts. Peltier elements have the advantage of being very small and requiring only electrical power for cooling Their cooling capacity and minimum temperature cannot compete with compression- and cryogen-based coolers. Like Peltier coolers, they only require electrical power, do not contain any potentially dangerous working fluids (only helium) or cryogens but have a significantly higher cooling capacity. Cryofocusing–thermodesorption units for our other GC–MS (gas chromatography – mass spectrometry) instruments (Hoker et al, 2015; Obersteiner et al, 2016), which are currently operated in the laboratory Both detailed description and characterisation of the preconcentration unit were not discussed in the publications by Hoker et al (2015), Obersteiner et al (2016; laboratory set-ups) and Sala et al (2014; aircraft instrument). CryoTel CT, Sunpower (Ametek), USA −80 (cooling capacity would allow < −120) 180–220 2 (1 tank) Baratron 626, MKS Instruments, Germany EL-FLOW F-201CM
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