Chromatography Forum

You have headspace ? If yes - not need liquid/liquid extraction.
In headspase you have liquid/gase phase extraction , very effective by acetic acid water solution. Acetic acid is high boiled, but vary volature liquide.
The sulfuric acid (in water solutions) not volature liquid. Quicly dead of column by cross-link phase will not. Effectivity of column , tailing factor - in you quest is secondary question.

I'm recomendate. Make the some water solution of acetic acid by concentration 10, 5. 1, 0.5, 0.1 mg /ml and analise it (headspace 80-90 C, 10 ml , after add 1-2 drop of concentrated sulfuric acid and Na2SO4 ). For (from) determerminate calibration curve linearity and sensivity of analitical method.
After that we will discuss results.

You've say "The sulfuric acid (in water solutions) not volature liquid". Can you explain to me why you've say it? I want understand. Thank you very much!

100,0% of acid remain in Head space vial? Some part vapour don't vaporize?

Thanks!

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Good luck with your research

Thanks for your interesting and for your understanding! I'll see your website!

Have a Good day!

If you can see "parts of compounds" in the hexane layer then they are not in solution, they are particles in solution. Try filtering the hexane layer through a syringe=tip filter after you do the extraction and before you inject the hexane layer onto the GC. Despite what Carl says you can cause all sorts of problems by injecting dirty samples.
Peter

Trying to keep things simple for this new user during these range finding experiments. Every sample is dirty, some worse than others. My undertsanding of the concern was sample dissolved in the hexane, not particulates. The user will have to clarify this.

Also, I'm still not convinced the LLE approach will work since acetic acid has higher solubility in water than hexane.

I'm glad to see DSP reviving the headspace discussion.

If using headspace I recommend using a single solvent that completely dissolves the sample such as DMF, DMSO, etc, to avoid baises caused by incomplete extaction of acetic acid from the core of particles. If using sulfuric acid (BP ~330 C) a small amount of acid will be in the vapor phase but this should not cause major problems with the GC column.

Hi Carl

If alemaggot can see compound in either the water or the hexane then what he is seeing cannot be in solution (unless his compound is coloured of course), it has to be particles in suspension. Why inject a dirty sample when there is an easy way to clean it up ?

Discussion of headspace methods is only useful if alemaggot has a headpsacer.

Peter

Yes guys, I've a head space sampler

Than... You advise me to use this method? Ok. You're all agree with kind DSP007 says?

Headspace would be great. Weight your sample into a vial, add sulfuric acid and run.

I suggest using a solvent mixture that completely dissolves your solid sample such as 90/10 DMF/1M aq H2SO4 (v/v) or 90/10 DMSO/1M aq H2SO4. Heat at 80C for 15min prior to injecting the headspace.

You have headspace ? If yes - not need liquid/liquid extraction.
In headspase you have liquid/gase phase extraction , very effective by acetic acid water solution. Acetic acid is high boiled, but vary volature liquide.
The sulfuric acid (in water solutions) not volature liquid. Quicly dead of column by cross-link phase will not. Effectivity of column , tailing factor - in you quest is secondary question.

I'm recomendate. Make the some water solution of acetic acid by concentration 10, 5. 1, 0.5, 0.1 mg /ml and analise it (headspace 80-90 C, 10 ml , after add 1-2 drop of concentrated sulfuric acid and Na2SO4 ). For (from) determerminate calibration curve linearity and sensivity of analitical method.
After that we will discuss results.

You've say "The sulfuric acid (in water solutions) not volature liquid". Can you explain to me why you've say it? I want understand. Thank you very much!

100,0% of acid remain in Head space vial? Some part vapour don't vaporize?

Thanks!

OK
Smell the first aqueous solution of sulfuric acid, then an aqueous solution of acetic acid.
In the first case there is no odor - sulfuric acid in an aqueous solution of non-volatile. In the second case you smell even a 1% acetic acid, acetic acid is volatile.

Likewise, if HS will enter into GC-acetic acid will be present in the vapor phase. A sulfuric acid is in liquide phase.But sulfuric acid remains in the liquid phase and does not get in the instrument .

Before you try sodium acetate you need to test whether or not you can see acetic acid when that is the only component in the sample.

Make up a 1% solution of acetic acid, and adjust you headspacer and GC settings until you can see a nice sharp peak that is not present when you analyse clean water. The halve the concentration of acetic acid and see whether the peak gets smaller. If it does it is probably acetic acid.

From the amounts of sodium acetate that you used it seems that the concentrations that you are expecting in your samples might be rather low. Can you confirm what concentrations you are expecting ?

Peter

Hi guys!

Tomorrow I've try the injection.

I've prepare two vials with about 1 g of sodium sulfate, 5 ml of sodium acetate solution 0,01 mg/ml in water. In one of this vials I've add 2 drop of sulfuric acid.

In the result of vial n 1 without sulfruic acid I've found about 41000 area units. In the second results, with acid, I've found about 27000 area units. Then is less.

How can we explain it?

Before you try sodium acetate you need to test whether or not you can see acetic acid when that is the only component in the sample.

Make up a 1% solution of acetic acid, and adjust you headspacer and GC settings until you can see a nice sharp peak that is not present when you analyse clean water. The halve the concentration of acetic acid and see whether the peak gets smaller. If it does it is probably acetic acid.

From the amounts of sodium acetate that you used it seems that the concentrations that you are expecting in your samples might be rather low. Can you confirm what concentrations you are expecting ?

Peter

Hi Peter!

In my product the sodium acetate limit is less than 0,02%. Usually there is a small residue of it after production (about 0,003 %)

[quote="alemaggot
Hi Peter!

In my product the sodium acetate limit is less than 0,02%. Usually there is a small residue of it after production (about 0,003 %)[/quote]

Whoops ! that is rather low. Acetic acid is difficult to do by GC at low levels. Maybe we should have found out the target concentrations four pages ago (or did I miss it before ?).

Let's see what the experts think.

Peter

Guys have you some news?

Guys have you some news?

mark

Guys have you some news?

mark

what?