Chromatography Forum

Good afternoon.

I would like to analyse impurities of phenol with GC-FID. There is an ASTM available (D6142) but this does not work.
The chromatograms in the ASTM are model components without an overload of phenol.

In real life phenol is in the middle of the chromatogram. Some components are liking phenol very much and so they show a "chair" like peak in the chromatogram. I know this phenomenon from large volume injections.
But how to get over this.
Normally the suggestion is to change solvent, but the solvent phenol is my sample as well. Because the impurities are < 5ppm, I can not dissolve my sample. I do add some 10% MeOH to keep the phenol liquid.

I have used a DB1 and a CP sil 19 column. I have other columns available but I don't think this will help.

Does anyone have a good method for me, before I start doing a lot of experiments.

thanks
Okkie

A possible solution depends on what the impurities are.

If the impurities are also phenols you might be able to react the whole sample with acetic anhydride under basic conditions to give the corresponding non-polar acetates.

If the impurities are not phenols, or other acids, you could dissolve the sample in weak aqueous base and extract the impurities into a non-polar solvent - the phenol will stay in the aqueous phase.

To reduce the solvent effects you are seeing with the chair shaped peaks you need to use the most polar possible column to reduce the difference inpolarity between the phenol solvent and the column.

You might actually get better results by putting less sample onto the column (with a split injection for instance) - the impurity peaks will be smaller but might have better shapes.

Good luck

Peter

Thank, I will try some of your suggestions.

Okkie