Retention index (RI) is a powerful tool for gas chromatography-based structure elucidation of various compounds. In this study, linear RIs based on n-alkanes and n-fatty acid methyl esters in different temperature programs were fitted. Nearly identical first-order linearities were acquired with different temperature programs. The linear equations were y=1.0051x+318.51 (r2=1) and y=1.0362x+562.519 (r2=1) for polar (packed with polyethylene glycol) and semi-standard non-polar (packed with 5% diphenyl/95% dimethylpolysiloxane) columns, respectively. The variables x and y in the equations stand for RIs based on n-fatty acid methyl esters and n-alkanes, respectively. The established linearity was then verified using the reference RIs collected in the NIST mass spectral library, Golm metabolite library, and Fiehnmetabolite library. The RI values converted using both the acquired equations finely matched those in the references. The established relationship between the two kinds of RIs can be used to expand the RI references and decrease the number of RI acquisition experiments.
Keywords: conversion; gas chromatography (GC); n-alkane; n-fatty acid methyl ester; retention index (RI).