Anal. Chem. 2005, 77, 6989-6998
Development of a Cryogen-Free Concentration System for Measurements of Volatile Organic Compounds Barkley C. Sive,*,† Yong Zhou,† Donald Troop,† Yuanli Wang,† William C. Little,‡ Oliver W. Wingenter,§ Rachel S. Russo,† Ruth K. Varner,† and Robert Talbot†
Climate Change Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824, MMR Technologies, Inc., 1400 North Shoreline Boulevard, Suite A5, Mountain View, California 94043-1346, and Department of Chemistry, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801
An innovative cryogen-free concentrator system for measurement of atmospheric trace gases at the parts per trillion level has been developed with detection by routinely used gas chromatographic methods. The firstgeneration system was capable of reaching a trapping temperature of -186 °C, while the current version can reach -195 °C. A Kleemenko cooler is used to create liquid nitrogen equivalent trapping conditions and eliminate the use of solid absorbents, a potential source of artifacts. The method utilizes dual-stage trapping with individual cold regions. The two stages are cooled to -20 and -175 °C for water management and sample enrichment, respectively. Both stages house a Silonite-coated stainless steel sample loop; the second stage loop is filled with 1-mm-diameter glass beads, which provide an inert surface area for analyte concentration. In our application, the complete system employed four channels utilizing two flame ionization detectors, one electron capture detector, and a mass spectrometer. The system was automated for unattended operation and was deployed off the New England east coast on Appledore Island to measure a suite of ambient non-methane hydrocarbons, halocarbons, alkyl nitrates, and oxygenated volatile organic compounds during the International Consortium for Atmospheric Research on Transport and Transformation field campaign in summer 2004. This robust system quantified 98 ambient volatile organic compounds with precisions ranging from 0.3 to 15%. Volatile organic compounds (VOCs; include non-methane hydrocarbons, oxygenated hydrocarbons, halocarbons, and alkyl nitrates) play key roles in the chemistry of the atmosphere1,2 and * Corresponding author. Phone: (603) 862-3132. Fax: (603) 862-2124. E-mail:
[email protected]. † University of New Hampshire. ‡ MMR Technologies, Inc. § New Mexico Institute of Mining and Technology. (1) Thompson, A. M. Science 1992, 256, 1157-1168. (2) Wang, Y.; Jacob, D. J.; Logan, J. A. J. Geophys. Res. 1998, 103, 1075710768. 10.1021/ac0506231 CCC: $30.25 Published on Web 09/23/2005
© 2005 American Chemical Society
have a number of anthropogenic and natural sources.3,4 Oxidation of non-methane hydrocarbons (NMHCs) produces a suite of free radicals that are involved in NOx (NO + NO2)-catalyzed reactions, which generate ozone (O3) in the troposphere.5,6 Subsequent photodissociation of O3 by UV light ( 0.92 over 1 order of magnitude change in ambient mixing ratios. It is worth noting that the strong correlations persisted even at sub-pptv mixing ratios, highlighting the excellent performance of the automated MMR-GC system. CONCLUSIONS Overall, the new MMR-GC system developed by our research group offers extremely high sensitivities and selectivity for measuring a large suite of atmospheric VOCs. Comparison of results obtained from this real-time system with well-established techniques clearly demonstrates its ability to provide high-quality measurements, even at sub-pptv mixing ratios. A major inherent advantage of the MMR-GC system is the capability to make accurate and precise VOC measurements in remote locations where cryogens, such as liquid nitrogen, are not readily available. Moreover, the system eliminates the use of solid adsorbents for
6998 Analytical Chemistry, Vol. 77, No. 21, November 1, 2005
the concentration of air samples, a method known to be prone to artifacts. The system operated autonomously for ∼5 months prior to deployment on Appledore Island and, more recently, for 6 months in the laboratory demonstrating its durability and reliability. One aspect of this multichannel system that has not yet been exploited is its versatility for measuring a wide variety of compounds in other applications. ACKNOWLEDGMENT Financial support for this work was provided through the Office of Oceanic and Atmospheric Research at the National Oceanic and Atmospheric Administration under grants NA17RP2632 and NA03OAR4600122. Additional support for the research conducted on Appledore Island was provided by the National Science Foundation through grant 0401622. This paper is contribution number 122 to the Shoals Marine Laboratory. We thank the Shoals Marine Laboratory and the Isles of Shoals Steamship Company for their assistance and support during the field campaign. Finally, we thank Lissa Ducharme and the UCI group, especially Dr. Donald R. Blake and Mr. Kevin Gervais. Received for review April 12, 2005. Accepted July 21, 2005. AC0506231
