Comparison of headspace techniques for sampling volatile natural products in a dynamic system

Commonly used dynamic sorption techniques for collecting biologically activ e volatile compounds have been compared. Solid phase microextraction (SPME) using two types of fibers (polydimethylsiloxane, PDMS, 100 mu m, and carbo wax/divinylbenzene, CW/DVB, 65 mu m) was compared to purge and trap methods (Porapak Q, Tenax TA and charcoal) and a technique based on absorption in methanol in a cooling bath. Sampling was done in a stream of purified air ( 20 ml/min) in a closed and temperature-regulated (27 degrees C) glass tube, passing over a capillary tube containing a hexane solution of tridecane, h eptadecane, 1-octen-3-ol, 1-hexadecanol, ethyl tetradecanoate, alpha-pinene , linalool, terpinen-4-ol, cis-verbenol, verbenone, beta-caryophyllene, E,E -farnesol, and geranylgeraniol. With all of the methods, the sampling was p erformed for a period of 30 min before extraction and analysis was done on a GC-FID system. In general, SPME gave a higher response for all compounds except for alpha-pinene, which was only extracted by the CW/DVB fiber. Purg e and trap methods and methanol absorption gave the same response for all s ubstances extracted. None of the methods extracted hexadecanol and geranylg eraniol under the conditions used. However, the SPME equipped with the PDMS coating extracted heptadecane, E,E-farnesol and ethyl tetradecanoate. Our results show that SPME, when selecting the fibers to fit the polarity and v olatility of the compounds, is an outstanding extraction method compared to purge and trap and methanol absorption, especially for a qualitative analy sis. The best conditions for storing fibers exposed to compounds of high vo latility were at low temperatures (6 degrees C) in sealed vials, while the worst way was to leave the exposed fiber unprotected at room temperature (2 2 degrees C). The dynamic sampling system was effectively tested on a fruit ing body of a polypore fungus (Ganoderma applanatum) emitting 1-octen-3-ol, and again SPME showed to be the most sensitive technique.