Kovats Index to Identify the exact Biomarker

Kovats Index is very important to measure a specific geochemical biomarker in the geochemistry field of research. The Kovats Index is used in the GCMSMS (Gas Chromatography-mass spectrometry mass spectrometry) analysis to identify unknown molecules from the data produced by the mass spectrometry measurements. Kovats Index is measured based on the retention time of organic molecules.

Definition of Kovats Index

Kovats indices of a molecule are the retention time normalized to adjacently eluting of n-alkanes. For example, if a molecules Kovats Index is 1427, then the retention time of that molecule is 14 mins and it indicates that the targeted molecules will appear in between C-13 and C-15 of two successive n-alkanes.

Here is the details example

Suppose, you want to identify the Cadalane (M/z; 198,168, 153) in the Agilent muss hunter software. At first, you have extracted the data with m/z, 198, 183, 168, 153.  You will get a peak but if you are not confirmed about the Cadalane molecule the apply the Kovats index.

 How To apply the Kovats Indices;

First, collect the saturated sample data of the same date measured with the Cadalane sample data, like F1a measured data for n-alkane F1b+2 for the Cadalane data.

Now, extract the F1a data of the same sample number with m/z 57 to get the n-alkane chromatogram. Then find out the n-alkane carbon number right and left side of the retention time of the expected peak in F1b+2 sample.

Suppose you got, an expected peak of Cadalane peat at 14.5 min in F1b+2 sample, and in the F1a sample the right and left side C number is  nC16 and nC-17. Then get there retention time also from the chromatogram for nC-16 and nC-17. Now apply the Kovats index formula in the excel file.

The formula of the Kovats index is; K=100*((LogTx-LogTcn)/(Logcn+1-Logcn))+100cn

After applying the formula if you get the same number for the standard Kovats index for the Cadalane and your calculation value. Then you have confirmed that the expected peak is the Cadalane Peak.

See the Fig Below;

Kovats index 
The formula of the Kovats index

Here are the detail link of Kovats indices;

 

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