For those who are experienced in GC of essential oils, is it really necessary the larger alkanes for Kovats indices calculation? I am working with monoterpenes (linear chain of C8) in a HP-Innowax column and targetting pinene, limonene, geraniol and myrcene (including alcohol/aldehyde derivatives etc). Despite the differences in the branching and presence of functional groups, should I use C20 and higher alkanes?
Also, I am extracting those compounds from mineral medium. I started with 50%Methanol quenching of cells, followed by chloroform trapping of non-polar compounds (isovolume added to methanol phase). Of course I have to analyse both phases in GC, but should I expect any monoterpene or oxygenated-derivative in the methanol phase? Thanks for the help
Dear Pedro Soares-Castro
i think in for qualitative analysis of of essential oils in GC-MS you not need to calculate the kovats indices, just try with Nist datebase search for identification organic componds.
regards
Dear Pedro,
I used a mixture from C8-C24, but I was also analyzing sesquiterpenes.
To isolate compounds from liquid medium we tested two methods, distillation and n-penthane. The solution with the solvent was mix for at least 3h, and then the solvent fraction was concentrated and analysed.
Good luck
Dear Pedro,
I have an experience working with essential oil analysis using GC-MS. I usually follow the method of Carovic-Stanko et al., 2010 (Carović-Stanko, K., Orlić, S., Politeo, O., Strikić, F., Kolak, I., Šatović, Z. 2010. Composition and antibacterial activities of essential oils of seven Ocimum taxa. Food Chemistry 119(1): 196-201)
I normally extract essential oil using hydrodistillation (for more detail, please see the proposed publication). I used C7-C30 mixture of linear alkanes (commercially available from sigmaaldrich website). The maximum retention time was around 24 minutes. It is also available for C8-C20. From my previous research, I did not observed any compound beyond 20 minutes (retention index circa 2300). I would recommend you to used C7-C30. Eventhough you focus on linear chain C8, retention index will be different depending on substitution. I also identified compounds using NIST Library.
Regards,
may be this is useful..
http://onlinelibrary.wiley.com/doi/10.1111/j.1750-3841.2011.02421.x/abstract;jsessionid=24B9A04CA4F581D66B59BD381E1B7F07.f04t02
The highest alkane that you need to inject is the samllest one that elutes after your last compound if interest. After that you are simply wasting run time.
Non-polar compounds like terpenes will partition into the chloroform, but not completely. You can estimate recovery in the chloroform by extracting the methanol twice and comparing the peak areas from the second extraction with the areas from the first. You then correct the areas from a single extraction for recovery.
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