Flight Data Update on Long-Term Compound Stability in Dual Sorbent Tubes

Dual Sorbent Tubes (DSTs) are currently the primary method for collecting volatile organic compounds in the cabin air of the International Space Station (ISS). Data from groundbased analysis of these archival air samplers provide a major component of the assessment of ISS air quality by the NASA toxicologist. At the 2005 ICES conference data from the positive control DSTs, returned on Soyuz 7S and 8S, were presented. Positive control tubes are dosed, preflight, with known concentrations of representative contaminant compounds and they are launched to ISS in the DST kit as trip controls. Upon return of the DST kit to the ground, results from analysis of the trip (positive) and laboratory control tubes are used to determine the recoveries: concentration of dosed compounds retained in the tube. Results from positive controls, returned on 7S and 8S showed substantial losses of some compounds dosed into the tubes 156 to 240 days prior to the analysis. Low recoveries are expected for spacecraft air contaminants with similar properties to the poorly recovered dosed compounds. It was shown that compound losses in the control tubes were consistent, which led to the generation of acceptable correction factors for spacecraft air contaminants. Correction factors decrease the accuracy of derived compound concentrations and substantial error could arise under some conditions. An investigation into the mechanism for compound loss is necessary before design modifications can be implemented to improve the DST performance. This paper will update results from the DSTs returned on Soyuz 9S and 10S missions during the latter part of 2005. The data acquired from these returned DSTs will be compared to the 7S and 8S data presented last year. Discussion will focus on the reliability of correction factors and identify any trends in the data. This paper will describe the experimental design and plans to identify the compound loss mechanism.