How To Calculate Kovats Index

Chromatography is the science of decomposing elements into separate compounds that can be identified and analyzed. Gas chromatography achieves this process by subjecting the substances to high degrees of heat so the gaseous components can be separated. Gas chromatography is one of the primary techniques used in forensics science, transportation security scans and drug testing labs. This procedure is one of the first tests performed after a sample has been separated into components, and it is used to identify each compound drawn from the sample. Kovats retention index is a mathematical tool used to assist researchers in identifying the compound and ascertaining a degree confidence in this discovery.

Step 1

Analyze the components. The content of each component is analyzed using three techniques: qualitative analysis (numeric assessment of known species), retention time (comparison of unknown species) and Kovats retention index (logarithmic scale on which adjusted retention times are compared with unbranched alkanes).

Step 2

Identify the formula. Kovats index(I) is calculated as I= 100[n + (N – n) x (Log tr (unknown) – logtr (n))/ logtr(N) – logtr(n)) where n equals the number of carbon atoms in the smaller alkane, N is the number of carbon atoms of the larger alkane, tr is in all cases the adjusted retention time (calculated at time – time of the undelayed small compound).

Step 3

Compute Kovats index. Given the complexity of this procedure, it is best to utilize existing software system designed to compute the indices automatically. Dionex, Chrom Perfect and Agilent Technologies offer software packages that support gas chromatography and provides the appropriate indices for analysis.