RETENTION INDEX CALCULATION BASED ON A NONLINEAR RELATIONSHIP BETWEEN NET RETENTION TIME AND CARBON NUMBER OF NORMAL-ALKANES

Methods of retention index calculation described in the literature have been based on a linear relationship between the logarithm of the adjusted retention times lg ts and the carbon numbers C of n-alkanes. Exact measurements of the retention times of n-alkanes show that the relationship lg ts=f(C) is in fact not strictly linear. Correct extrapolative or interpolative calculations of retention indices over a wide retention range are therefore impossible when using the original formula as given by Kovats or methods based on a linear regression concept. The method of retention index calculation presented here is based on a cubic relationship between lg ts and carbon number allowing extrapolative or interpolative calculations. The hold-up time (tm) is calculated on the basis of differences of retention times of the reference homologues. © 1979 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH.