Studies of the ionization chemistry in the re-circulation loop of the differential mobility spectrometer analyzer used to monitor air quality in the international space station

Abstract

In-flight monitoring of volatile organic compounds on the International Space Station (ISS) has been routine since 2009 using gas chromatography, with a preconcentration inlet, and a differential mobility spectrometer detector; first as a station detailed technical objective (SDTO) instrument and then as the air quality monitor (AQM), a fully integrated instrument including imbedded computer for control and data acquisition. A combination of AQM with an atmospheric pressure ionization mass spectrometer was developed to allow exploration of instrument behavior associated with the composition of the internal re-circulated gas atmosphere. The first aspects of AQM to be explored using the AQM-mass spectrometer included explanations for mobility drift of the negative reactant ion peak, methanol, and acetaldyehyde peaks (carbon dioxide in the gas recirculation loop) with operation on ISS. The AQM-mass spectrometer system helped ascertain the identity of artifact peaks in the negative polarity associated with materials in the flow system of AQM. Further experiments investigated the influence of water from humidity in ambient air, which is absorbed on the preconcentration trap during sampling and desorbed into the gas chromatograph-differential mobility spectrometer (GC-DMS) measurement and the incorporation of a trap purge to reduce effects of water co-eluting with target contaminants.