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The Effect of Air Bubbles and Headspace on the Aqueous Concentrations of Volatile Organic Compounds in Sampling Vials |
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| Authors: | Farhad Nadim Shili Liu PhD George E Hoag PhD |
| Institution: | Farhad Nadim is a research staff at the En ironmental Research Institute. (Uni ersity of Connecticut, U-5210 Storrs, CT 06269–5210; 486–4015;fax 486–5488;). He recei ed an M.S. in environmental engineering from the University of Connecticut in 1996. He has conducted extensive bench-scale and pilot-scale research studies for remediation of soils contaminated with light and heavy petroleum products, coal tar, and chlorinated solvents.;Dr. Shili Liu;received his Ph. D. in analytical chemistry from the University of Connecticut in 1990. Upon receiving his degree he has worked at the Environmental Research Institute (University of Connecticut, U-5210 Storrs, CT 06269–5210; 486–2586;fax 486–5488;) as the laboratory director since 1990. Dr. Liu's research interest is in environmental chemistry and environmental analytical chemistry. He has extensive experience and knowledge in trace organic compounds analysis. Dr. George E. Hoag;is a professor of civil and environmental engineering at the University of Connecticut and the executive director of the University's Environmental Research Institute, which he founded in 1987 (University of Connecticut, 270 Middle Turnpike, Longley Bldg., U-210, Storrs, CT 06269–5210. ). After earning his Ph.D. in environmental engineering at the University of Connecticut in 1983, he joined its department of Civil and Environmental Engineering as a faculty member. Dr. Hoag's research areas include the fate and transport of organic chemicals in soil and ground water systems and the development and design of remediation processes for soil and ground water cleanup at hazardous waste sites. |
| Abstract: | The presence of headspace and air bubbles in volatile organic analysis sampling vials lowers the actual aqueous concentration of these compounds due to the partitioning of solutes into the gaseous phase. This could make the sample invalid for analysis. In this work, the effects of air bubbles and headspace on the aqueous concentration of 60 volatile organic compounds listed in U.S.Environmental Protection Agency (U.S. EPA) Method 8260 were evaluated experimentally and theoretically. The results showed that for air to water ratios of 1 to 20 and less, there was no significant effect on the aqueous concentrations of target organic solutes in the sampling vials. When the air to water ratio was increased to 1 to 10, the recovery rates of four organic compounds were lower than the control. Laboratory experiments on sampling vials showed that the presence of air bubbles or headspace with the volumetric air to water ratios of 1 to 20 and less do not produce any significant effect on the original concentrations for most targeted volatile organic compounds. The experimental results also indicated that in 40 mL sampling vials with headspace range of 2 to 8 mL, the recovery rates of most volatile organic compounds with high values of Henry's law constant (> 0.01 Atm m |
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