A new method to improve olfactory responses to GC effluents.

Biological detectors such as the human nose or an insect antenna represent extremely attractive detectors for gas chromatography (GC) since they are specifically tuned to perceive biologically relevant compounds. However, these detectors are nonlinear, noisy and often perform poorly under standard GC conditions since they are adapted to detect transient rather than long-lasting stimuli. These drawbacks can be overcome if the chemical stimulus, delivered by the gas chromatograph, is re-shaped (modulated) before reaching the biological detector. We describe a pulsing system that improves the performance of an insect olfactory system when stimulated with the effluent from a GC capillary column. Chemicals eluted from the GC column are trapped and rapidly desorbed within a thermal modulator in order to transform the continuous effluent into a succession of short-pulsed stimuli. The output from this modulator was directed to an insect antenna, from which electrophysiological responses were recorded. The system was evaluated with adult male Spodoptera littoralis (Lepidoptera: Noctuidae) stimulated with the conspecific female sex pheromone. Results obtained with this new approach indicate that both sensitivity and reliability of the biological detector are improved compared with the classical technique. Possible developments of this new technique are discussed.