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United States Department of Agriculture

Agricultural Research Service

Title: AIR-FLOW RATE IN THE QUANTITATION OF VOLATILES IN AIR STREAMS BY SOLID-PHASE MICROEXTRACTION (SPME)

Authors
item Bartelt, Robert
item ZILKOWSKI, BRUCE

Submitted to: Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2000
Publication Date: N/A

Interpretive Summary: An existing technique for measuring amounts of organic compounds in the air was broadened in scope to increase its flexibility and functionality. Solid-phase microextraction (SPME) is a rather new, commercially available method for sampling organic compounds from the air. The technique is sensitive, easy to perform, and does not involve potentially dangerous solvents. SPME can be an especially useful method for measuring air-borne concentrations of pheromones and other important insect attractants, either from living organisms or from synthetically prepared dispensers. Such measurements are vital for understanding insect biology and also for evaluating pest management techniques involving behavioral chemicals. SPME sampling is done by placing the source of the chemicals in a vessel with an air stream passing through it and then placing the tip of the syringe-like SPME device in the air outlet. Previously, the air-flow rate had to be chosen from four specific settings in order for the calculations to be possible. In this research, the properties of SPME were studied under a wide range of air-flow rates, and an equation was developed so that the calculations can now be done successfully for any flow of air that is convenient and relevant for a particular project. The research further simplifies the use of this powerful new analytical tool and greatly broadens its scope.

Technical Abstract: Solid-phase microextraction (SPME) is a useful technique for quantitation of air-borne volatiles. We previously developed a method for the 100-micron poly(dimethylsiloxane) fiber type that allowed quantitation even when equilibration with the fiber coating was not complete. The key feature of the method was that it was dynamic; sampling was from an air stream, which led to a relatively simple mathematical description of equilibration kinetics. The method was relevant for an extensive range of analytes, sampling temperatures, and sampling times, but only for four specific air-flow configurations. The present study was conducted to broaden the scope of the method to allow a wide range of air-flow rates. This was done by characterizing absorption kinetics for 21 different air flow rates ranging over two orders of magnitude. The measurements were made for n- alkanes of 11 to 18 carbons; thus both rapidly and slowly equilibrating compounds were considered. Overall, 766 data points were acquired. Non-linear regression analysis was used to develop an equation that related the efficiency of SPME extraction to air-flow rate. This equation was then incorporated into the previous model, so that there is now wide flexibility with respect to air-flow rate as well as to compound type, sampling time, and temperature. As before, absolute quantitation by SPME does not depend on attainment of equilibrium and does not require prior calibration of the individual fiber. Finally, simulations are presented that demonstrate how the choice of air-flow rate can affect quantitation.

Last Modified: 8/27/2014
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