Chromatography Forum

I've got a sample with an mixture of anorganic acid (0-5% H2SO4) and organic acids and I like to determin isopropanol.

I'm using a capillary silica column with FID-detection, but I'm afraid that the acidity will damage my column. It's pH 3-4 and that's quit low for silica, I thought.

Can someone tell me of it's possible to inject this sample direct in the GC or do I have to do some 'pre-staps' ???

Thanks,

Jorim

PS. I'm just an student without massive experience...

You could neutralise your solution,and use headspace for Isopropanol...

Headspace is always preferred when doing residual analysis if it can be done well.

Since you have acids present (I can assume an aqueous solution, although you have not chosen to give us that information), putting acids or neutralized acids (salts) on a GC column is not a good idea in general (although it has been done).

Placing a retention gap ahead of your column and removing it after the analysis is completed is a good precaution. Use 1 to 5 meters of an old column or uncoated tubing. You can also use a packed injection liner to trap most of the really acidic components as an alternative.

On the other hand, if this is only a homework project and you don't want to damage your grade as well as your column, I would keep my temperatures low enough not to volatilize any acids downstream into my column yet high enough to volatilize the carrier solvent and my IPA.

I would carefully neutralize the inorganic acids(especially one like HF) and do SPME or headspace analysis. Direct injection can be done especially if you use a packed injection liner.

Good luck

Chromatographer1

If I knew more about the solution and its composition I could give better advice.

Since you have acids present (I can assume an aqueous solution, although you have not chosen to give us that information), putting acids or neutralized acids (salts) on a GC column is not a good idea in general (although it has been done).

Yes aqueous solution, forgotten to say, but your answer is already a good help, thanks..

It's a little bit difficult to tell you more because I don't know very mutch myself.

- Some organic acid's haven't an idear witch
- 0-5% H2SO4
- It contains IPA
- Soluted in water

That's it

And can you fill me in on headspace. I've heard and read about it on school but I forgot the basic's...

Thanks,

Jorim

Headspace is often an automated technique where the 'matrix' is dissolved in a minimum of solvent, heated in a sealed vial, and the gas space above the liquid in the vial is sampled from the vial and injected onto a GC column.

It can also be done manually but that is difficult to do well.

SPME can be done manually and low cost, often with good results, in comparison to HS.

Headspace is often used in determining blood alcohols and other difficult matrices which are difficult to extract volatiles for analysis. It is accurate with internal stds and even without internal stds when done well over a large range of measurement of low ppb (1ng) to percent levels (10µg) with proper selection of sample size, vial volume, and sampling loop or timed injection parameters.

I hope this helps your memory.

Chromatographer1

I hope this helps your memory.

Yes it does...

Thanks