Ground-based measurements of halogenated substances using GC/MS

The group uses two different systems of gas chromatography (GC) coupled with mass spectrometry (MS) for ground-based measurements of halogenated compounds. Both contain a cryogenic enrichment-unit, a gas chromatograph and one or two mass spectrometers. Due to the comparatively small mixing ratios of the halogenated substances present in the atmosphere (parts-per-trillion), the enrichment unit is of high importance. For enrichment, halogenated substances get frozen onto an adsorbent agent. Following desorption and gas chromatographic separation, the substances are detected in the mass spectrometer.

At the Taunus Observatory air is measured in situ several times per day with a time-of-flight mass spectrometer coupled to a gas chromatograph. This mass spectrometer-type is sampling over a certain mass range continuously, without the need to pre-define target substances. Thus, a digital archive is generated, which allows future retrospective analysis of yet unidentified substances or substances which are not yet in the scientific focus.

For the offline analysis of air samples which are collected in canisters, a GC/MS-system with two mass spectrometers is available in the working group’s laboratory. This system contains, next to another time-of-flight-MS, a quadrupole mass spectrometer. The quadrupole-MS exclusively detects defined target substances with high technical reliability, measurement accuracy and linearity.