Hi,
I am trying to extract and identify the composition of essential oils from hemp inflorescences. I have to run an alkane mixture, but the one available at the lab is from C16-C40. Do you think I need lower RMM alkane mixture to help me in the identification? For example: at least from C6 - C30.
Also, if I use Adams (2007 or earlier editions) to compare the retention values and mass spectra of each component; does it make sense that I use the same column type and temperature programme Adams mentions in the book? Usually the one I use is a DB-5HT (30m.0.25x0.25), with a non-isothermal (ramp) temperature programme.
Thanks for your help!
Here is an old publication on KI which has been quoted by several authors. Contact Chandan S. Chanotia an experienced researcher in the field of essential oils.
Good luck
Dear Maria Magro,
C8-C25 or C8-C30 n-alkane series/mixture are good for analyzing essential oil components. However, C6-C30 series is also equally good (as you mentioned) for determining retention index of the essential oil components. Moreover, for using Adams reference book for the identification of essential oil constituents, it is necessary to analyses your samples on the similar stationary phase as used in the reference book. If you use other stationary phases, then the resulting elution order of the components will be different from those reported in the reference book. In this situation, it would be very difficult for you to compare the RI and mass spectrum of the constituents. Further, you may use similar or slightly different temperature programming for the analysis of your essential oil samples. The temperature programming doesn’t affect the retention index values of the constituents. It is important to mention here that the n-alkane mixture and essential oil samples should be run under the similar temperature programming.
Good Luck
I hope that this reference will help in this research. My regards.
http://www.hc-sc.gc.ca/hc-ps/pubs/precurs/tech-man-eng.php
Check the answers in this related thread
https://www.researchgate.net/post/Can_anyone_suggest_the_sample_preparation_method_for_alkane_series_C8-C20_injection_in_GCMS
Dear Maria,
Using Kovats indices (KI or RI) is rather indicative, and should be confirmed with data from GC/MS analyses.
If you do not have C6-C16 alkane series, you might tentatively calculate your RI by use of the difference between the retention times of two consecutive alkanes (ex. RtC17-RtC16) by substracting to obtained subsequent values until C6. But this gives you only indications. Try and see...
On the other hand, while attempting to identify essential oils components, RI should be compared using data from similar types of columns (polar with polar, and non polar with non polar).
Good luck,
Fabrice
Hello:
There is another good reference : V.I. Babushok, P.J. Linstrom and I.G. Zenkevitch, Retention Indices for frequently reported compounds of Plant Essential oils, J. Phys Chem. Ref. Data, 40(4), 47 pages (2011).
Good luck.
Guy
Hello!
I think you can also use these websites:
http://webbook.nist.gov/chemistry/ (It´s a webbook from NIST and you can find the Kovats Retention Index of so many volatile compounds in different stationary phases and in different temperature programs)
http://www.pherobase.com/kovats/ (Here you can calculate the Kovats Retention Index of your compound based on the retention time of the n-alkanes)
Good luck,
Aura
You did not mention whether you have the Adams electronic database (most helpful) to go along with his book. We recently had an Agilent engineer program our GCMS for a custom installation for essential oil applications. If you have Agilent gcms, then you are in real luck b/c the design of quadrupole etc is like the one Dr. Adams used to compile the database. We get spectra that are amazingly similar to his, so much so that retention time matching is not absolutely necessary. We did obtain a new inert column to try to match his, and use his ramp temp program. We performed Retention Time Locking so that hexadecane standard elutes in 32 minutes using constant flow. For the smaller, lighter monoterpenes, our retention times are about one minute longer than Adams'. Not a problem b/c the spectral matches are so fabulous, and our retention orders are the same. You may contact me if you like- I have Dr. Adams' email address.
Hi Everyone,
First of all thankyou everyone for the helpful suggestions! I really appreciate!
Secondly, I only have an e-book version of Adams, but I think someone at the lab has a hard copy of his book. Do you think it's enough?
I am using a n-alkane mixture of C8-C44 - so this should be suitable for my identification.
Again, thankyou for your help!
If you have a mass spec detector on your gc, you may want to consider installing Dr. Adams' electronic database. He sold me one for US $750. It contains every spectrum in the book. Its advantage over NIST is that it has retention times and indices, which are not available in the NIST libraries.
You can follow the links below and can also download the pdf of the articles attached herewith to obtain certain crucial informations:-
1. http://www.farm.ucl.ac.be/Full-texts-FARM/Herent-2007-1.pdf
2. http://www.nist.gov/srd/upload/jpcrd402011Ret.pdf
Hello,
For those who are experienced in GC of essential oils, is it really necessary the larger alkanes for Kovats indeces 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, not so much related with the kovats topic, 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
Pedro,
I am running essential oils on Agilent DB5-ms ultra inert column on the same analytes as you. (per R. P. Adams' method).
We are retention time locked to n-hexadecane, but we have electronic database for comparison and do not worry much about the indices.
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