Wood vinegar preparation

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

32 posts Page 1 of 3
Hi all,

I have been approached by one of my colleagues to see whether it is possible to analyse wood vinegar using GC-MS. Now I have no experience in the area of wood vinegar and my colleague has no experience of GC-MS and after looking around at some papers I am not entirely sure how to prepare the sample for analysis. I was thinking of placing a SPME fibre into the wood vinegar then thermally desorbing it in the GC injection port.

Does anyone have any suggestions?

Cheers,

Joe
Hi Joe

From wikipeadia

Wood vinegar = The principal components of pyroligneous acid are acetic acid, acetone and methanol. It was once used as a commercial source for acetic acid. In addition, the vinegar often contains 80-90% water along with some 200 organic compounds.

So in answer to your query, yes, SPME into the headspace or into the liquid would work and I would suggest a polar column e.g. Innowax. A good general purpose fibre for this would be a DVB/ carboxen fibre

see http://www.sigmaaldrich.com/technical-d ... ibers.html

Others may have a better experience/ recommendations on this

BUT, from experience (e.g. have you got a hammer? - when what they really needed was a screwdriver - true example) it is easy to get mislead on a query that pre supposes a particular approach -in this case SPME :-)

Do you have any more details on the target analytes and the purpose of the analysis? It may be helpful for others to formulate a better reply


Regards

Ralph
Regards

Ralph
Hi Joe

You'll get a chromatogram using SPME - whether it tells you what you need to know about the vinegar is not guaranteed, whether it's the best method is another question.

How are the mites doing ?

Peter
Peter Apps
GOM wrote:
Hi Joe

From wikipeadia

Wood vinegar = The principal components of pyroligneous acid are acetic acid, acetone and methanol. It was once used as a commercial source for acetic acid. In addition, the vinegar often contains 80-90% water along with some 200 organic compounds.

So in answer to your query, yes, SPME into the headspace or into the liquid would work and I would suggest a polar column e.g. Innowax. A good general purpose fibre for this would be a DVB/ carboxen fibre

see http://www.sigmaaldrich.com/technical-d ... ibers.html

Others may have a better experience/ recommendations on this

BUT, from experience (e.g. have you got a hammer? - when what they really needed was a screwdriver - true example) it is easy to get mislead on a query that pre supposes a particular approach -in this case SPME :-)

Do you have any more details on the target analytes and the purpose of the analysis? It may be helpful for others to formulate a better reply


Regards

Ralph


Hi Ralph,

I hope you're keeping well?

Wikipedia was also my first port of call when I was approached with this query, and when I saw 80-90 % water I had some reservations as I was told to keep samples containing water away from the GC-MS at all costs.

It would be great to be in a position to purchase a non-polar column for this analysis, but as my colleague only wants to analyse it out of curiosity I can only run the sample on the non-polar HP5-MS column I currently have installed. Similarly I don't really want to spend money on new SPME fibres so I only have 75 um Carboxen/polydimethylsiloxane at my disposal.

I suppose I did ask a bit of a pointed question there!

The purpose of the analysis is just to scope out the chemical components that make up the wood vinegar, so there are no target analytes particularly.

Cheers,

Joe

PeterApps wrote:
Hi Joe

You'll get a chromatogram using SPME - whether it tells you what you need to know about the vinegar is not guaranteed, whether it's the best method is another question.

How are the mites doing ?

Peter


Hi Peter,

I hope you're keeping well?

I suspect it isn't the best method, but the analysis is just a preliminary investigation to see get a general idea as to what compounds make up the wood vinegar.

The mites are doing very well, thank you. I haven't replied to the other thread recently as I have been focussing on undertaking some of the behavioural assays using silica extracts from a number of different mite species. Once I have the behavioural data, I intend to pursue the GC-MS work further. I actually found a modified version of your pipette tip idea for filtering the silica gel from my solvent after extraction: https://www.agilent.com/en-us/products/sample-preparation/sample-preparation-methods/filtration/selectionguide. These syringe filters fit onto the end of a leur lock hamilton syringe, so I can use a wide gauge needle to suck up my sample then swap over the tip and then push down the plunger to filter my sample. It seems to work relatively well and provides no contamination when compared to the centrifuging technique. I hope to be able to update everyone once I have finished the work!

Cheers,

Joe
Hi Joe

Thanks for the update

For acetic acid and similar polar analytes you really need a polar column (like dissolves like)

From experience the fibre that you have would work but on a low polarity phase like HP5 you will get a tailing peak for a polar compound.

The water will not be a problem

For other analytes it may work

If it just out of curiosity and you are just doing a favour then just do it with what you have and see what you get - then you can worry about the chromatography and ask questions afterwards :-)

My philosophy is work with what you have and see what happens - then figure out how to make it better - an heuristic approach :-)

Regards

Ralph
Regards

Ralph
GOM wrote:
Hi Joe

Thanks for the update

For acetic acid and similar polar analytes you really need a polar column (like dissolves like)

From experience the fibre that you have would work but on a low polarity phase like HP5 you will get a tailing peak for a polar compound.

The water will not be a problem

For other analytes it may work

If it just out of curiosity then just do it with what you have and see what you get - then you can worry about the chromatography and ask questions afterwards :-)

Regards

Ralph


Hi Ralph,

If the work ever progresses further than a preliminary investigation into the chemical composition of the wood vinegar then I will certainly invest in a polar column.

I'm not too concerned about the quality of the chromatogram at this stage, just whether I can ID a few of the major compounds.

As I've never used a SPME fibre for anything other than headspace analysis (mostly aphid honeydew VOCs), how much wood vinegar should I submerge it into and for how long? What sort of GC settings should I use for a piece of investigative work such as this (oven temps, temp ramps, etc)?

Sorry for all of the questions!

Cheers,

Joe

EDIT: This paper is the closest I have been able to find to what I want to do, but the methods are a little lacking in detail: https://www.researchgate.net/profile/Dinesh_Bilehal/publication/231337961_Gas_Chromatography-Mass_Spectrometry_Analysis_and_Chemical_Composition_of_the_Bamboo-Carbonized_Liquid/links/0fcfd50692628825f4000000.pdf
Hi Joe

It's good strategy to focus on the mite biology first and then go to the chemistry. Keep us posted.

For the vinegar try a literature search on vinegar authenticity or origin - I thought that I had some papers on it but I cannot find them.

Peter
Peter Apps
Peter Apps wrote:
Hi Joe

It's good strategy to focus on the mite biology first and then go to the chemistry. Keep us posted.

For the vinegar try a literature search on vinegar authenticity or origin - I thought that I had some papers on it but I cannot find them.

Peter


Hi Peter,

Thanks for the guidance on the literature. From what I have seen, a lot of authors are using SPME just to analyse the headspace of various vinegars. Some authors add NaCl to their sample prior to sampling, what could the possible reasons for this be? They're not stated in the papers and I'm intrigued.

Cheers,

Joe
Generally adding salts, especially NaCl, to a solution prior to sampling the headspace is to decrease the solubility of the target analytes.
If the concentration of acetic acid is large, you might struggle with a SPME phase that is too absorptive. I ran some white vinegar that I have and I doctored it up by adding 2.2% acetone and 2.2% methanol. The vinegar is 5% acetic acid already. I was able to see all 3 analytes easily with a 100% PDMS SPME fiber, a BP-20 (wax column from SGE) using headspace analysis. I only used a flame detector on the GC.

Those mixed phases of SPME fibers work best for analysis of the trace components in the mixture.
This is probably already more elaborate than you want for a suck it and see first pass - but if you raise the pH you will get rid of the huge acetic acid peak with acceptably minor effects on the neutral compounds. Adding sodium carbonate until it stops fizzing gives you high pH and salting out in one go.
Peter Apps
Steve Reimer wrote:
Generally adding salts, especially NaCl, to a solution prior to sampling the headspace is to decrease the solubility of the target analytes.


Hi Steve,

Thanks for pointing me in the right direction with this, I have now managed to find a nice review article that explains the benefits of adding salts to a solution prior to headspace analysis.

Cheers,

Joe

[quote='rb6banjo']If the concentration of acetic acid is large, you might struggle with a SPME phase that is too absorptive. I ran some white vinegar that I have and I doctored it up by adding 2.2% acetone and 2.2% methanol. The vinegar is 5% acetic acid already. I was able to see all 3 analytes easily with a 100% PDMS SPME fiber, a BP-20 (wax column from SGE) using headspace analysis. I only used a flame detector on the GC.

Those mixed phases of SPME fibers work best for analysis of the trace components in the mixture.[/quote]

Hi rb6banjo,

I suspect that purchasing new columns and SPME fibres will be out of the question as my colleague only wanted to analyse it out of curiosity. Thanks for your reply though, I find this sort of thing absolutely fascinating.

Cheers,

Joe

[quote='Peter Apps']This is probably already more elaborate than you want for a suck it and see first pass - but if you raise the pH you will get rid of the huge acetic acid peak with acceptably minor effects on the neutral compounds. Adding sodium carbonate until it stops fizzing gives you high pH and salting out in one go.[/quote]

Hi Peter,

I may try adding sodium carbonate and using SPME in the headspace. Thanks for the suggestion.

I saw another method that details adding NaCl before extracting with diethyl ether. However, it doesn't state how much salt they added or the volume of vingegar. Is there a typical weight of salt you add to a sample in these situations?

Cheers,

Joe
HI Joe

Saturate it with salt - with salt and vinegar flavour you can't go wrong !

As a fun exercise compare the aroma of unsalted and salted vinegars, that will tell you is your are getting an effect.

Peter
Peter Apps
Salt and vinegar flavoured wood chips - love it - made me smile

As usual you have had some good suggestions - I particularly like the 2 for one effect from neutralisation of the acetic acid.

Since it is just out of curiosity and working with what you have why not try for a start

Headspace sampling for 1 min at ambient temp of

a) 1ml sample
b) 1 ml sample + 300mg of salt
c) 1ml of sample after neutralisation with sodium carbonate or bicarbonate
d) 1 ml water + the amount of sodium carbonate required in c) above as a blank in case it contains adsorbed volatiles

Don't spend too much time on it - you are looking at volatiles in a wide range of concentrations.

It will be an interesting learning curve for you

From experience the volatiles at a lower concentration may require 5 mins sampling at 65°C to capture and identify

Ralph
Regards

Ralph
Know that the addition of the carbonate salt will titrate all of the acidic species (carboxylic acids, phenols, maybe thiols, etc.) in the solution so you likely won't see them anymore. Some things may also react at high pH - ester hydrolysis for instance. My philosophy on this sort of thing is do as little "harm" to the sample as possible until you realize that conventional means are not going to get you where you want to go. I would analyze the wood vinegar straight at first and then see what I get. If you find that the acidic species are of little interest, then add the carbonate salt to go after the neutral species and the basic species. A salt like sodium chloride is the best way to create high ionic strength yet not change the reactivity of the medium a great deal.
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