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 s pecifically tuned to perceive biologically relevant compounds. However, the se detectors are nonlinear, noisy and often perform poorly under standard G C conditions since they are adapted to detect transient rather than long-la sting stimuli. These drawbacks can be overcome if the chemical stimulus, de livered by the gas chromatograph, is re-shaped (modulated) before reaching the biological detector. We describe a pulsing system that improves the per formance of an insect olfactory system when stimulated with the effluent fr om a GC capillary column. Chemicals eluted from the GC column are trapped a nd rapidly desorbed within a thermal modulator in order to transform the co ntinuous effluent into a succession of short-pulsed stimuli. The output fro m this modulator was directed to an insect antenna, from which electrophysi ological responses were recorded. The system was evaluated with adult male Spodoptera littoralis (Lepidoptera: Noctuidae) stimulated with the conspeci fic female sex pheromone. Results obtained with this new approach indicate that both sensitivity and reliability of the biological detector are improv ed compared with the classical technique. Possible developments of this new technique are discussed.