[Peacock]

Dear all,

I want to extract a carboxylate from a small quantity of aqueous solution (2 ml) by acidifying it. Then I expect that the volatile organic acid formed dissolves in the organic phase.

Is it a must that the density of the organic solvent is lower than water?
Does The volatility of the chemical oblige to choose a less dense one?

Regards

[Borek]

Density doesn't matter, what matters is partition coefficient.

Just don't forget which phase should be collected.

[Peacock]

Hi, thanks for your reply

I thought that, to avoid traces of chemical escaping the liquid, the organic solvent had to be above the aqueous phase. Is this correct?

On another matter, how do I separate the organic phase from such a tiny amount of liquid?
Let's say that you have both phases in a test tube. Are there commercial solutions to this little problem? (big for me though at the moment).

Regards

[skbuncks]

On your first point I'm not quite sure what you mean. Where are these chemicals escaping too?

On such a small scale just suck the lot up (ater shaking in a test tube) into a plastic pasteur pipette, then holding it vertically allow the layers to separate. You can then carefully squeeze out the lower layer. Re-extract the aqueous layer with a further portion of solvent to ensure complete extraction.

skb

[Peacock]

I thought they could be released to the air contained into the vial.

I have found a solvent that does the job, i.e. ethyl acetate. However, I want to derivatise the carboxylate, and I need it to be dry.

 I don't know how to dry such a small sample of organic solvent (2-3 ml). If I add the traditional anhydrous salts, I take the risk of loosing the entire organic phase through adsorption. 

Do you know the customary procedure in such cases?

Regards

[skbuncks]

What solvent are you using for the derivatisation?
You will need to remove the EtOAc via vacuum distillation and solvent swap into your dried derivatisation solvent. Repeat distillations with this dried solvent should remove any traces of water.

skb