Dear Senthamizh,
I think you are referring to the Kovats retention indices.
They seek to try to define the retention of compounds analysed by GC by bracketing them with the nearest straight chain alkane hydrocarbons and a complex formula is used to obtain the Kovats retention index.
It may be an attempt at absolute identification of compounds according to this index.
I may be alone or out on a limb but I prefer relative retention indices which are much simpler, and although not absolute, seem to be very useful for helping to identify compounds in a group of analytes of interest in a laboratory setting.
The reproducibility of the relative retention times seems almost to be to great for the accuracy of most electronic clocks in modern integrators.
Hope this helps,
Kind regards,
Dr John
Dear Senthamizh,
I think you are referring to the Kovats retention indices.
They seek to try to define the retention of compounds analysed by GC by bracketing them with the nearest straight chain alkane hydrocarbons and a complex formula is used to obtain the Kovats retention index.
It may be an attempt at absolute identification of compounds according to this index.
I may be alone or out on a limb but I prefer relative retention indices which are much simpler, and although not absolute, seem to be very useful for helping to identify compounds in a group of analytes of interest in a laboratory setting.
The reproducibility of the relative retention times seems almost to be to great for the accuracy of most electronic clocks in modern integrators.
Hope this helps,
Kind regards,
Dr John
Dear Senthamizh,
Dr. John is right.
Basically, Kovats was a scientist who record the relationship between target compound with respect to the straight chain alkane (n-alkanes) before and after the target compound.
For example; your target compound retention time is 5min, and n-alkane C10and C-11 retention time 4 and 6 respectively.
The retention time relationship of that compound almost remains constant for that compound on such class of columns with respect to these two n-alkane.
Kovat's retention Indices normally represent by I.
I, is a measure of the retention of a solute relative to the retention of normal alkanes at a given temperature and column.
The I, for a normal alkane is its number of carbons e.g. nC12H26 has I=1200. If a solute has I=1478, it elutes after nC14 and before nC15, and it is closer to nC15.
Regards,
Dr Tariq
Thanks a lot Dr.Tarig,. is there any formula for calculation of retention indices?. also people are saying that ethyl ester retention indices. if the retention time of heptane-6 min, octane-7 min and my peak - 5 min the what is the retention index of the interest peak; how the analytical method will involve in the calculation?
Many Thanks
Selavn
According to Kovats your target peak should by lay between two ends in such case your result is not accurate or in other words you can not able to calculate the indices.
for Isothermal Analysis
I= 100n+100(N-n) x {log t (Analyte)-log t (n) / log t (N)-log t (n)}
where,
n= smaller n-alkane
N=lager n-alkane
t = retention times
Ethyl ester retention indices is new term for me i will try to find then i will say any thing.
regards
Hopefully the following site is useful to you
http://onlinelibrary.wiley.com/doi/10.1002/ffj.1887/pdf
We have made a webinar that could be of interest to you: http://www.chromatography-gc.com/webinars/webinar-molecules-raw-material-identification-comparison-library-retention-index/
3 min 25 sec: Process to convert Retention Time into Retention Index
5 min 33 sec: Molecular identification
10 min 27 sec: Raw Material Identification
17 min 10 sec: Raw Material Comparison in Retention Index Library
Dear,
Here is the excel file i have prepared with the KOvats Indices formula. Hope this will help you.
Have a good day.
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