The Impact of Water Vapor on Thermal Desorption Gas Chromatography
Volatile organic compounds (VOCs) pose significant environmental effects by promoting the production of tropospheric ozone and secondary organic aerosol. Isoprene is a VOC that accounts for 44% of the annual global VOC flux.1
Atmospheric concentrations of VOCs are low, often in the sub-ppb range.1 Analysis of these compounds through gas chromatography (GC) requires preconcentration, often in the form of thermal desorption (TD). The TD-GC method requires sorbent tubes, which filter air and selectively trap compounds on the tube. When the tube is heated in the TD unit, VOCs are released from the sorbent and introduced to the GC system.
Carbon molecular sieves (CMSs) are emerging in many areas of research as they are among the most powerful sorbents, capable of adsorbing compounds with higher volatility ranges than other TD-compatible sorbents.2,3 While CMS sorbents are sought after for their high selectivity, their sorbent strength poses a unique challenge as water molecules are easily adsorbed. Ambient air samples collected above 40% relative humidity can introduce water vapor on the sorbent material and detrimentally affect VOC collection.4 These water molecules prohibit the adsorption of other VOCs, thus interfering with accurate collection and quantification. The consequences of water collection on chromatographic analyses have been observed, though a thorough analysis of water effects on TD-GC sampling is rarely described. The mechanism behind which CMSs work, the interaction of the water molecules, and the resulting chromatographic issues will be discussed.
(1) Guenther, C.; et al. J. Geophys. Res. 1995, D5, 8873-8892
(2) Rungta, M.; et al. Carbon 2017, 11, 237-248
(3) Tanco, M.A.; Tanaka, D.A. Processes 2016, 4(3), 29
(4) Maceira, A.; et al. Sci. Total Environ. 2017, 599, 1718
Speaker: Mary Jean Riches
Speaker Institution: Colorado State University
Event Date: 08-23-2017
Event Time: 4:00 PM
Event Location: Chemistry A101
Mixer Time: 3:45 PM
Mixer Location: Chemistry B101E
Host: D. Farmer