[mofeta]

Gas Chromotography Olfactometry

The recent thread on GC for weed got me thinking. I made a post that mentioned how the type of detector(s) that you hooked to your column(s) was of prime importance.

I didn't want to clog the thread, but there is an interesting detector that is very useful for certain types of compounds. It is more sensitive than MS, FID or any other electro-chemical detector for these compounds. The cool thing about this detector is that it is extremely inexpensive (free), and easily available.

It is the human nose!

Using your nose as a detector with GC is called gas chromotography olfactometry (the term olfaction means "sense of smell"). It really is as simple as sniffing the analytes as they elute from the end of the GC column! For smelly compounds, the nose has a much lower threshold of detection than any machine.

I was wondering if any members here have tried this with weed? If so, please tells us about it!

[Shcrews]

but how do you calibrate your nose?

[mofeta]

Originally Posted by Shcrews

but how do you calibrate your nose?

LOL! Good question!

The instrument is self calibrating. The detector comes integrated with a powerful processor called the piriform cortex, that is very reliable and maintenance free. It stores highly accurate profiles for the various analytes, and is very precise and accurate.

[Shcrews]

thanks for the +rep.

i am still kind of confused about how this would be applicable to testing for, say, THC percentage.

[mofeta]

It wouldn't.

This would only be good for the aroma compounds, the terpenes/terpenoids.

At first, this was pretty much just a qualitative technique, but methods have been developed to quantify the analytes too.

[megayields]

So it tells you how good your boo smells? I am as dumb as a rock on this one???

[mofeta]

The chromatograph separates the compounds and spits them out the end of the column one at a time. This allows you to smell the various pure compounds that make up the complex, overall bouquet of the herb as individual components.

Sometimes when a compound is eluting from the column into the detector, the detector is not sensitive enough, and doesn't register the compound. With highly smelly compounds, like the ones that make pot smell, the human nose could tell you the compound was there when a electro-mechanical detector was saying there was nothing there. You could then take further steps to identify the compound.

[FlowerTops]

Just out of curiosity, how many terpenoids and flavanoids have been identified separately? Wouldn't a combination of 2 or more terpenoids create alltogether different terpenoid in terms of effect?

[highonmt]

Originally Posted by mofeta

The chromatograph separates the compounds and spits them out the end of the column one at a time. This allows you to smell the various pure compounds that make up the complex, overall bouquet of the herb as individual components.

Sometimes when a compound is eluting from the column into the detector, the detector is not sensitive enough, and doesn't register the compound. With highly smelly compounds, like the ones that make pot smell, the human nose could tell you the compound was there when a electro-mechanical detector was saying there was nothing there. You could then take further steps to identify the compound.

Not likely ime maybe if you had a trained labrador....Really this is like the old german chemists smelling everything and tasting it as well. Also, do not do this with an injected sample as the organic solvent is also coming off the column. It could work if you were looking for real smelly thiols or selenols but just turn your dector up to max and even minor impurities will turn up just above the noise. Or run a gc ms for chemical formulas of the minor impurities.
HM

[mofeta]

Originally Posted by highonmt

Not likely ime maybe if you had a trained labrador..

This technique has been widely used on perfumes, foods, spirits, wines and beers for over two decades. Here is a quote from a book about citrus:




Whether the human nose could beat the detector on the various smelly compounds in pot, well, maybe not, but I think it would be fun to try.

Originally Posted by highonmt

..Really this is like the old german chemists smelling everything and tasting it as well.

LOL! They were bold alright! They learned a lot that way though (some died too!) That's the way CAM (Crassulacean Acid Metabolism) was discovered, by people noticing that some species of succulent plants tasted sour at night, and sweet in the day.

Originally Posted by highonmt

Also, do not do this with an injected sample as the organic solvent is also coming off the column.

I think they use headspace, SPME, and subcritical water for extractions in GC-O a lot. They use organic solvents too. I think the solvent is carried out of the stationary phase by the carrier gas separately from the other compounds, just like the analytes come out one by one. As long as you were not sniffing when the solvent eluted, you would be OK. Am I wrong about this?