More History

Over the next 30 years sniff ports began to incorporate design features found in gas phase olfactometers while sniffer training and data handling methods began to include some of the practices commonly used in sensory testing. Taken together all these methods can now be called gas chromatography – olfactometry (GC/O). The importance of GC/O in the analytical chemistry of flavor and fragrance materials is as significant as gas chromatography – mass spectrometry (GC-MS) in spite of GC/O’s greater noise, bias and higher cost. This is because the specific sensitivity of GC/O for odorants often exceeds the sensitivity of GCMS by several powers of ten. The reason for this sensitivity is the ingenious design of the human olfactory system.

There are two parts to the olfactory system of all organisms that exhibit olfaction: (1) transduction or a process for converting a pattern of chemicals into electrochemical impulses that are transmitted to the brain and (2) pattern recognition programs that the brain uses to convert these impulses into precepts that mediate behavior. The point at which transduction takes place is on the surface of tissue located at the top of the nasal cavity called the olfactory epithelium. Recent studies have confirmed that the receptor sites on the olfactory epithelium are proteins that loop in and out of the receptor cell membrane seven times, a characteristic of what are called “seven transmembrane G-protein coupled receptors”. These olfactory receptor proteins are extremely sensitive and selective systems with biological cascades that amplify signals in much the same way photomultipliers electron cascades. What is interesting about the structure of these receptor proteins is that they have a primordial design. They are among the simplest of the G-protein coupled receptors and they share their structural features with different species. This implies that different species may “smell” the same or similar chemicals in much the same way different species respond to the same wave lengths of light. In fact the olfactory receptor protein is similar to opsin the receptor protein in the visual system(3). Thus many organisms may have similar transduction systems differing mainly in their pattern recognition programs. Therefore, it is not surprising then that GC/O has been used to identify insect pheromones and weasel scent gland components(4, 5). This article will summarize the technical development, application and potential use of GC/O to measure the odor of objects. However, it is not possible to give a complete account of the history of GC/O since much of its development and use has been in industrial laboratories under proprietary secrecy.