Gas Chromatography or the Human Nose — Which Smells Better?

Over millions of years of human evolution our senses have developed as our needs have changed. One of our main senses — triggered by the olfactory receptor genes — is smell. Studies show a reduction in the number of viable olfactory genes as humans evolved, with only 350 genes now used out of an original 1000, the remainder now unused. Vision became more important for humans as we moved to an erect posture. Our eyes moved to the centre of our faces and our noses became smaller, as it moved away from the ground with its rich tapestry of smells.

Better than Dogs?

Despite the reduction in the number of active receptor genes, recent behavioural studies suggest that humans in general have a well-developed sense of smell when compared with other descendants of our ancestors. Although we have fewer gene receptors than many other mammals, our sense of smell is in some instances better. In tests conducted comparing dogs and humans and their ability to detect low thresholds of certain odours, dogs could smell short-chain compounds better than humans, but surprisingly, humans were better on some longer-chain compounds.

GC v Your Nose

Studies also show that when compared with instrumentation — even sensitive gas chromatography (GC) detectors — humans can outperform the most sensitive of equipment in odour threshold tests.

Does this mean that olfactory instrumentation has no role to play in analysis?

The answer is no. Although the human nose is good and as humans we can describe smells - something a GC cannot do - there is a wide variation between individuals in the detection level and in the response we might have to a smell ­.

The advantage a GC has over humans is that it can break a smell down into its component parts and quantify the component parts — but it cannot say whether each component has a smell. And this has meant that systems have been developed to take advantage of both the GC and the nose — GC-O or more usually GC/MS-O.

Introducing Gas Chromatography – Olfactometry (GC-O)

GC-O is a widely used technique in the fragrance and food industries. As an example, it is also used to re-create a wine aroma, which you can read about here. A companion technique is GC/MS-O which combines the GC with a mass spectrometer to provide a more powerful and sensitive instrument.

The set-up uses a standard GC and detector, except that after the column the sample is split between the GC detector and a sniffer. This allows a human detector to assess each component of the sample individually. The advantage of the system is that the person can state which components have a smell and which don’t, whilst the GC detector can assign an identification to each component. A fragrance manufacturer can then assign a smell to each component smell, and so build a database of smells that can be used to build future fragrances.

Image Source: Smelling a Rose