Chromatography Forum

Hi Bart

Yes, perhaps I am excluding others (e.g. nonenal) by concentrating too much on that musty descriptor. Especially since you appear to have the sensitivity to detect the usual suspects.

Does everyone who smells the sample use that musty descriptor?

Another extraction technique that can be useful is to use a cheap version of the Gerstel stir bar. (A giant SPME )

I used 3mm OD PDMS tubing cut into 1cm lengths. These I baked or pre- extracted to remove residual volatiles. They are useful for headspace sampling in awkward samples like a tee shirt or in the mouth or just placing into an aqueous sample.

1 or 2 pieces can be thermally desorbed by dropping into the liner - a bit fiddly - or extracted with 0.5ml 50/50 CHCl3/methanol.

Below is an example of fungal volatiles from a fabric using this technique




I have some of this tubing and can always post some to you if you wish to have play.

Regards

Ralph

Hi Ralph,

Discribing odors is always difficult, especially when it is not in your native language (dutch). It think musty fits best, but I must say that for me there is a hint of wet iron or wet concreet to it as well.

Regarding the DIY stirbar. I might come back to you on this one.
At first I'd like to get my GCMSMS up and running again so I'm able to inject the SPE-extracts. I hope this will give me some more information.

thanks
Bart

Hi Bart

Thanks for keeping us updated.

I fully appreciate your comments about the descriptor. Wet iron/rust and concrete I understand. They are consistent with musty from a biological source

When I was doing GCMS-sniff port I would try to use more than one assessor because we all have different sensitivities and anosmias.

For example with axilla steroids - some people can smell them ( I find them to be musky.) some can't smell them and 1 in a 100 people will find them nauseating.

I would always ask assessor to say
"Now" so that I could record the time and later match it up with the chromatogram ( with my home made sniff port there was a 4 second delay between the sniff port and it then reaching the MS)

I also asked assessors not to think but just to say the first thing that came into their head, no matter how stupid it may seem.

The most intriguing comments from one assessor were

Ping pong balls
Wet crocodile
Minty worms
Death
Old tramp

I don't try to think about what he did outside work

vriendelijke groeten

Ralph

p.s.

From experience - If you use a glass funnel for your home made sniff port - the gas flow will be along the inner edge of the funnel wall rather than out from the centre. So use a really small nose sized funnel
edit It is the Coanda effect

Unless your sniff port is heated you will get condensation of odours on the glass that will linger and cause problems.

p.p.s.

Like you, all my colleagues from Belgium (and the Netherlands) here in the UK speak perfect English. Dutch/Flemish is so difficult

p.s.

From experience - If you use a glass funnel for your home made sniff port - the gas flow will be along the inner edge of the funnel wall rather than out from the centre. So use a really small nose sized funnel Ok we'll do

Unless your sniff port is heated you will get condensation of odours on the glass that will linger and cause problems. If nescessary, I'm planing on using the SSL injector for the snif port. While injecting on the PTV. It is heated and this way I can add e.g. N2 gas as carrier for the SSL and create some more volume while the DPFC is used for the He flow through the column. The N2 flow is adjustable by a needle valve (this gc only has one DPFC)

p.p.s.

Like you, all my colleagues from Belgium (and the Netherlands) here in the UK speak perfect English. Dutch/Flemish is so difficult thanks; google translate is a great help for technical terms.

Ralph,
Your post gets my vote for post of the year. Not only to the point with great, subtle and even arcane information but I laughed really hard as well. It was so good I showed it to my brother (a physicist) who could appreciate the funnel wall flow effect as well as the odor descriptors. Thanks for sharing.

Hi Aidnai

It made me laugh as well!

Tell your brother to look up the Coanda effect

It is why you can't extinguish a lit candle by blowing at it through a funnel - a useful party trick challenge

Regards

Ralph

Small update:
the SPE extract (aprox 1l water on a 1ml C18 cartidge and eluted with 1ml CH2Cl2) did not show any peaks that were not present in the blank.

We'll just keep on trying (in between the routine work).

Did the extract evaporated on a bit of filter paper have the musty odour ? - if so it means your extraction is working but your analysis is not.

Peter

After the CH2Cl2 evaporated (ppfff turned me a bit ) it did in fact smell musty, but the odor is not as strong as I would expect from an extract. It is not that much stronger than the sample itself.

I'm thinking: would it be possible to be looking for a compound that elutes together with the CH2Cl2? If so I'll never see it cause its in my solvent delay.

I'm scanning 50-650m/z, The chance that it is a compound with a mass <50 is rather small I guess. (?)

Would it be usefull to try and put 2 spe-cartridges on top of eachother? One with a C18 and the other with e.g. C8. If the compound is not trapped well by a C18 and passes through, it might catch on the C8. I don't have anough sample to do the test twice and this way it might work.

Hmmmmm........

If the extraction is working you should get an extract that is a lot stronger than the sample. Two possibilities are that the C18 does not catch the musty smell - in which case the sample that passes through will still smell musty - or that the C18 extracts it from the water but CH2Cl2 does not elute it from the cartridge (it's ages since I did SPE but I vaguely recall that non-polar solvents are not good eluters ???) in which case the musty odour is still on the cartridge and might come off with methanol (if you still have it).

Peter

I'm afraid it's been to long so I no longer have the cartridge.
But I'm planning on redoing the test and elute with MeOH.

Problem there is that this MeOH has to be spiked in CH2Cl2 to inject. So it will dilute again, or cause bad peak-shapes if to much MeOH is present.

In your opinion would it be necessary to use different SPE-types?
C18 and Oasis HLB are in stock for sure, I might find some C8. if other types are better, we can order them.

BMU

Reading through the question and responses, is there a reason you couldn't manually sample the headspace with a syringe and run a splitless injection?

That could avoid the issue with the SPME adsorption/desorption and solvent.

I'm afraid it's been to long so I no longer have the cartridge.
But I'm planning on redoing the test and elute with MeOH.

Problem there is that this MeOH has to be spiked in CH2Cl2 to inject. So it will dilute again, or cause bad peak-shapes if to much MeOH is present.

In your opinion would it be necessary to use different SPE-types?
C18 and Oasis HLB are in stock for sure, I might find some C8. if other types are better, we can order them.

BMU

I extract nearly all my samples (faeces and urine on soil) with methanol, and inject it as is - inlet temperature 240C, wax column start temp 50C, splitless I min with no problems (except I get methyl carbamate as an artifact of reaction between methanol and urea).

What little I ever knew about SPE I have pretty much forgotten - someone else here can surely advise.

Peter

Thinking about the comment of the odor being wet iron, is it possible it is inorganic in nature?

Also you may want to scan to lower masses if it is something along the lines of formaldehyde which would evaporate with the MECL which would leave little odor from the evaporated extract.

Reading through the question and responses, is there a reason you couldn't manually sample the headspace with a syringe and run a splitless injection?

We've already done that but we couldn't find any peaks different from the blank.

The MeOH extract has a musty odor so my unknown is in it.
I'll try some different techniques to get it analysed. I have very little experience with SSL liq injections (I mainly do 50µl CH2Cl2 PTV injections) but I'll have a go.

thanks again for all the input it is much appreciated!!!