IRMS - Isotope Mass Spectrometry
The working group "Stable Isotopes in Aerosols" analyses the stable carbon isotope composition of atmospheric organics in gas and particle phase. Compound specific measurements are carried out by using TD-GC-IRMS (Thermal Desorption - Gas Chromatography - Isotope Ratio Mass Spectrometry). The main goal is to identify and quantify the sources and the atmospheric chemical processing of volatile organic compounds (VOC) as well as of organic aerosols. Research activities include:
- laboratory investigations to determine the kinetic isotope effect (KIE) of atmospheric relevant reactions as well as to scrutinize the mechanisms of secondary organic aerosol (SOA) formation and evolution;
- investigations to determine the stable isotope composition of aerosols in source- and ambient field samples
Two TD-GC-IRMS setups are used for off-line isotopic analyses: the gas phase setup and the aerosol setup. Both systems consist of a custom built cryo-sampling thermal desorption unit (TD) connected to a gas chromatograph (GC) coupled to an isotope ratio mass spectrometer (IRMS) via a combustion interface:
- within the gas phase setup, the cryo-focussing system is optimized to concentrate collected trace gases prior to separation. Three thermal-desorption-cryo-trapping steps are operated successively to attain an optimal focussing of the VOCs;
- within the particle phase setup, the thermal desorption and transmission of the VOCs from the aerosol filter samples to the GC is optimized by using a Thermal Desorption Unit (TDU), mounted directly onto a Programmable Temperature Vaporizing Cooled Injection System (CIS). Two-Dimensional Gas Chromatography (2DGC) is used to optimally separate polar organic compounds.
The GC-separated VOCs are transferred to a combustion interface and oxidized quantitatively to CO2 and water. The later is removed in a water trap, whereas the CO2 is transferred to the isotope ratio mass spectrometer for stable carbon isotope ratio measurement.