Chemical Ecology, Göteborg University, Box 461, 405 30 Göteborg, Sweden.
An evaluation of the HS-SPME technique (headspace solid phase microextraction) was made with regard to the importance of fibre coating on the amounts of collected volatiles. Three different fibre coatings were tested; polydimethylsiloxane/divinylbenzene (PDMS/DVB) 75 µm, carbowax/divinylbenzene (CW/DVB) 65 µm and carboxene / polydimethylsiloxane (CAR/PDMS) 65 µm, all supplied by Supelco. A test mixture of 21 compounds, common in volatile analysis of biological material, was released from an open capillary at room temperature to a closed vessel (volume 16 ml) into which the SPME fibre was inserted for adsorption. After adsorption of the headspace volatiles, the compounds were analysed on a GC-MS and the different compounds were identified from the resulting spectra. Each compound was then quantified based on its arbitrary abundance and compared to an external standard curve. The study showed that the optimal desorption time, under the given premises, was 30 seconds for all three SPME fibres. The equilibrium times clearly differed between the compounds tested and, in many cases, between the different SPME fibres used. Highly volatile compounds reached their equilibrium time within 4 minutes, while many of the less volatile compounds had not reached the equilibrium after 60 minutes. When compared to traditional aeration of volatiles (Teflon columns packed with Porapak Q adsorbent), the HS-SPME technique rendered a larger number of compounds registered with all fibre coatings, but at lower amounts than with the adsorbent Porapak Q.