Chromatography Forum

Hi all again!

As I wrote in my previous topic today, basically, I analyze essential and fatty oils (raw material) for pharmaceutical use, using GC-FID equipment and European Pharmacopoeia methods.
But my boss wants that I quantitatively analyze the mixture of oils.

For example first mixture will contain 3 oils:
-Tea tree oil - 1g
-Eucalyptus oil - 1g
-Olive oil - 98g (as solvent)
Composition of the mixture and oil percentage (+-) will be always known.

The only idea I have, how to analyze such mixtures, is to make some external calibration using some specific peaks for each oil. I don't need to analyze solvent oil, but I need to know quantity of Tea tree oil and Eucalyptus oil.
Probably I will not use any complex sample preparation, only dissolution in Heptane.

Is it possible to create such method and whether this method will show normal results?
Also is it dangerous to inject fatty oils in GC only dissolving it, without esterification reaction?
Also do I need to use some internal standard, to calculate relative response factor?

May be someone have a better idea of method for such analysis?

Cheers,
Dmitrij

For example first mixture will contain 3 oils:
-Tea tree oil - 1g
-Eucalyptus oil - 1g
-Olive oil - 98g (as solvent)
Composition of the mixture and oil percentage (+-) will be always known.

The only idea I have, how to analyze such mixtures, is to make some external calibration using some specific peaks for each oil. I don't need to analyze solvent oil, but I need to know quantity of Tea tree oil and Eucalyptus oil.,
Dmitrij

You need to key on what in the mix is different than the overwhelming amount of triglyceride (olive oil).

The British Pharmacopoeia states that eucalyptus oil must have a minimum cineole content of 70% if it is pharmaceutical grade. That is tons smaller than triglycerides/olive oil, I would assay for cineole

Tea tree oil has a bunch of terpenes, also way smaller than triglycerides. Assay for those.

I agree with CPG. Those lighter things are much easier to deal with compared to the triacylglycerides as well. SPME is a great technique for sampling the headspace above the oil mix for the volatile materials. I was just working out a method for determination of aldehydes in vegetable oil and it turned out very well. I did learn that injection of this type of sample into the GC via a merlin microseal is not a good idea. The oil that condensed on the syringe barrel apparently destroyed the seal (it became evident after a number of injections). After that last injection, it wouldn't seal anymore.

A good, old fashioned rubber septum works beautifully.

I agree with the others.

SPME headspace and use target compounds

I have the ESO2000 database of some 4000 analyses of essential oils - due to large variations in composition from different sources use the actual oils that you have as standards and target cineole for the Eucalyptus oil and Terpinen-4-ol for the Tea tree oil

Regards

Ralph