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GENERATION AND CALIBRATION OF STANDARD GAS MIXTURES FOR VOLATILE FATTY ACIDS USING PERMEATION TUBES AND SOLID PHASE MICROEXTRACTION
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: Pp. 009-016 in Air Pollution from Agricultural Operations III, Proceedings of the 12-15 October 2003 Conference (Research Triangle Park, North Carolina USA), Publication Date 12 October 2003. 701P1403.(doi:10.13031/2013.15493)
Authors: Jarett P. Spinhirne and Jacek A. Koziel
Keywords: permeation tubes, standard gas generation, volatile organic compounds, volatile fatty acids, solid phase microextraction, gas chromatography, air sampling, odor
Volatile fatty acids (VFAs) are major components of odors associated with agricultural operations and livestock housing, solid waste processing and disposal, and industrial and municipal wastewater collection and treatment systems. Emissions estimation and assessment of odor control methods depend on reliable air sampling and analysis methods for VFAs. The objective of this research was to develop and test a method for continuous and reliable generation of standard gas mixtures for VFAs based on permeation tubes. Standard gas mixtures for acetic, propionic, isobutyric, butyric, isovaleric, valeric, and hexanoic acids were generated with permeation tubes and monitored for a 100-day period. The gravimetric loss of VFA from each tube was measured periodically and used to calculate the emission rate for each permeation tube. Emission rates were as high as 2,011 ng/(min·cm) for acetic acid to as low as 49 ng/(min·cm) for isovaleric and hexanoic acids, respectively. The emission rate was combined with the dilution flow rate to calculate standard concentrations. Five different concentrations for each VFA were obtained by adjusting dilution flow rate. Gas concentrations were monitored with DVB/Carboxen/PDMS 50/30 µm fibers using triplicate 1 min extractions. Maximum standard gas concentrations ranged from 21.9 ppmv for acetic acid to 0.22 ppmv for hexanoic acid. Minimum standard gas concentrations ranged from 3.0 ppmv for acetic acid to 0.03 ppmv for hexanoic acid. The relative standard deviations (RSDs) for all VFA concentrations ranged from ± 1.6 % to 7.56 %. Rapid SPME extractions were sufficient to preconcentrate significant amount of VFAs for separation on a GC-FID without derivatization. Dilution gas flow rate did not affect the emission rates from permeation tubes. In contrast, low acid levels affected permeation rates of the acids from the tubes. Methodology described in this research paper could be used to generate and test standard gas mixtures for other groups of odorous gases.
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