ingect series hydrocarbon from C10 to c 28, at the same colume and condition, then use espeial Equation for calculate the values for each compounds, the Adams book, GC-ms analyssis for essential oil

Thanx Dr. Gamal el baroty for your nice suggestion.

Hello. I did a little explanation for you to observe how we calculate the Kovats indices (attached).

Now with the attachment.

Kovats indices should be used ONLY for isothermal analyses, which are not the best condition for essential oils.

If you use a temperature program you should use linear retention indices (LRI) calculated similarly to Kovats ones, but using a modified formula according to Van den Dool and Kratz. See here:

http://webbook.nist.gov/chemistry/gc-ri/

Thank Dr. Guido Flamini for your important information regarding KI. Do you use internal standard (Hydrocarbons) for getting real KI value in GC-MS?

Yes, I use the series of n-alkanes from C-7 to C-25

Thank Dr. Guido Flamini for your nice suggestions.

Thank you Eduardo Ethur. very useful pdf!! searched a lot for such an explanation. 

Hi,

If I use the Van den Dool and Kratz, to determine the identity of essential oils and other plant metabolites; from which literature can I compare my calculated value. I know that Adams uses Kovats; can I use this book to compare the calculated retention indices?

I am using a GC temperature ramp program, therefore it is a non-isothermal analysis.

Also, the alkane mixture is ready available or I can prepare it myself?

Thanks!

Hi Maria,

the last edition of Adams (2007) uses linear retention indices.

Hi Guido,

I have an older edition of Adams.  Do you know from where I can have access of the 2007 edition?

And does it make sense to use a retention mix of alkanes from C16-C30 to help me calculate retention indices of essential oils?

Thanks a lot for you help!

Dear Maria,

you can obtain the book from the publisher http://www.alluredbooks.com/reviews/Iden_Esse_Oil_Comp_Gas_Chro_Mass_%20Spec_4th_Ed_rev.pdf

I suppose it is also on Amazon or similar sites.

In my opinion you should also use lower alkanes. I use the series of n-alkanes from C-7 to C-25 

Thanks for the link!

Yes that makes sense - that I use a lower n-alkane series.  I can prepare them myself? Example: put a mixture of heptane, octane, nonane, decane, etc?  Do I have to order them from somewhere?

I really appreciate your help! thankyou!

You can both prepare by yourself or order a commercial mixture. I obtained mine from Sigma-Aldrich

Thankyou ! 

Hi,

If I want to analyse a wide range of lipid in my sample (inc. fatty acid, alcohol, hydroxy acid and alkane), is it suitable to use the same approach? I mean the using series of alkanes to calculate retention index of my compound?

Many thanks!

Thanks for valuable information

(Kovats, 1958).

KI = 100 [ n+ (N-n) x log t1R (unknown) – log t1R (Cn)/log t1R (CN) – log t1R (Cn)]

t1R – the net retention time (tR – t0)

t0 – the retention time of solvent (dead time)

tR – the retention time of the compound.

CN – number of carbons in longer chain of alkane

Cn– number of carbons in shorter chain of alkane

n - is the number of carbon atoms in the smaller alkane

N - is the number of carbon atoms in the larger alkane

We use the non-isothermal Kovats retention indices (from temperature-programming) using definition of Van den Dool and Kratz (Van Den Dool, H., Kratz, P.D., J. Chromatography, 1963, 11, 463-471).

I am also looking for this as am not able to calculate KI value for my oil data