The Kovats index applies to organic compounds. The method interpolates peaks between bracketing n-alkanes. The Kovats index of n-alkanes is 100 times their carbon number, e.g. the Kovats index of n-butane is 400. The Kovats index is dimensionless, unlike retention time or retention volume. For isothermal gas chromatography, the Kovats index is given by the equation:
where the variables used are:
* , the Kováts retention index of peak i
* , the carbon number of n-alkane peak heading peak i
* , the retention time of compound i, minutes
* , the air peak, void time in average velocity , minutes
The Kovats index also applies to packed columns with an equivalent equation: