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United States Department of Agriculture

Agricultural Research Service

Title: Relative Humidity and Its Affect on the Analysis of Volatile Fatty Acids on Sorbent Tubes

Authors
item Trabue, Steven
item Scoggin, Kenwood
item Koziel, Jacek - IOWA STATE UNIVERSITY

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: September 2, 2005
Publication Date: September 2, 2005
Citation: Trabue, S.L., Scoggin, K.D., Koziel, J.A. 2005. Relative humidity and its affect on the analysis of volatile fatty acids on sorbent tubes. Proceedings of Animal Agriculture and Processing: Managing Environmental Impacts, August 31-September 2, 2005, St. Louis, Missouri. 2005 CDROM.

Interpretive Summary: Understanding how volatile fatty acids (VFA) affect air quality from animal feeding operations (AFO) is important. In fact, many researchers have identified VFAs as the key class of volatile organic compounds (VOC) emitted from swine farms and the dominate odor associated with swine operations. Consequently, accurately measuring VFA levels in air around AFO is important. Analysis of VFA in air using thermodesorption (TDS) has been proposed as a method of choice, but water in the atmosphere is a major interference in TDS analysis of VOCs. Relative humidity conditions in animal feeding operations (AFO) are especially high and pose several limitations in VFA analysis using TDS analysis. However, reducing the amount of water adsorbed via choice of adsorbent material or procedures used in TDS analysis all reduce interferences of water to acceptable levels. The objective of this study was to measure the effect relative humidity had on the breakthrough volume of various sorbent materials (tenax, graphitized carbon, and carbon molecular sieves) and the effect of adsorbed water had on TDS analysis. Breakthrough volumes for acetic and propionic acids on sorbent material increased according: tenax being less than graphitized carbon which was less than carbon molecular sieve. This suggests that carbon molecular sieve material was the best sorbent material for trapping VFAs in air; however, sorption of water on these sorbent materials reduced their effectiveness in trapping VFAs in air. Water sorption onto each tube increased according: graphitized carbon being less than tenax which was less than carbon molecular sieve material. Water adsorbed onto tubes caused significant retention time shifts for early eluting VFA with adsorbed volumes of 10 microliters (mg) or more resulting in poor chromatography and poor reproducibility. Problems associated with adsorbed water were best managed by splitting column flow from the thermodesorption unit prior to the gas chromatography (GC) inlet. This method will enable researchers the ability to measure accurately VFA in the ambient air around AFO and to determine the effect VFA have on air quality.

Technical Abstract: Volatile fatty acids (VFA) are a major component of odor from swine operations. Thermodesorption has been used in the analysis of VFA in air; however, no study has been conducted to validate this air sampling technique. The objectives of this study were to determine the effects relative humidity had on the breakthrough volumes of VFA for various sorbent materials (tenax, graphitized carbon, and carbon molecular sieves) and the effect sorbed water had on their analysis. Breakthrough volumes for acetic and propionic acids on sorbent material increased according: tenax being less than graphitized carbon which was less than carbon molecular sieve. Water sorption onto each tube increased according: graphitized carbon being less than tenax Which was less than carbon molecular sieve material. Water sorbed onto tubes caused significant retention time shifts for early eluting VFA with sorbed volumes of 10 microliters or more resulting in poor chromatography and poor reproducibility. Problems associated with water were best managed by splitting column flow from the thermodesorption unit prior to the GC inlet.

Last Modified: 10/24/2014
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