Submitted to: Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/1996
Publication Date: N/A
Interpretive Summary: Because of environmental concerns about pesticides, our research focuses on utilizing naturally occurring volatile chemicals from plants, insects, and microorganisms to help monitor crop pests. Research related to interactions among organisms and the chemicals depends on the ability to accurately measure the amounts of volatile chemicals in the air. Solid-phase microextraction (SPME) is a rather new technique for collecting volatile organic compounds from the air. SPME promises to be a powerful tool in studying the composition and biological activity of scents emitted from living organisms. Complex volatile mixtures can be collected rapidly, simply, efficiently, and without using solvents; the sample is then analyzed immediately by gas chromatography. Uniform SPME devices are now commercially available, but methods have been lacking to quantify the amounts of compounds in the air by SPME. The present study provides calibration information and a set of practical guidelines so that the commercial SPME devices can be used for this purpose. The result is a rather general and simple quantitative method that should be of considerable interest to scientists in future studies of biological volatiles.
Technical Abstract: Solid-phase microextraction (SPME) is a versatile new technique for collecting headspace volatiles prior to GC analysis. The commercial availability of uniform SPME fibers makes routine, practical quantitation of headspace concentrations possible, but calibration information for SPME has not been available. Calibration factors (amount absorbed by the fiber divided by headspace concentration) were determined for 71 compounds using SPME fibers with a 100 um poly(dimethylsiloxane) coating. The compounds ranged from 1 to 16 carbons in size and included a variety of functional groups. Calibration factors varied widely, being 7000 times higher for tetradecane than for acetaldehyde. Most compounds with a Kovats retention index of <1300 on a nonpolar GC column (DB-1) equilibrated with the fiber in 30 min or less. A regression model is presented for predicting calibration factor from GC retention index, temperature, and analyte functional class. Calibration factor increased with retention index but decreased with increasing sampling temperature. For a given retention index, polar compounds such as amines and alcohols were absorbed by the fibers in greater amounts than were hydrocarbons. Henry's law constants determined using SPME were in general agreement with literature values, which supported the accuracy of the measured calibration factors. An unexpected concentration dependence of calibration factors was noted--especially for nitrogen-containing and hydroxy compounds; calibration factors were relatively higher (SPME fiber was more sensitive) at lower analyte concentrations.