The hold-up time in gas chromatography -: III.: Linearity of the plot of ln t′R of the n-alkanes vs. carbon number questioned

Three arguments are presented to show that the plot of the logarithms of the adjusted retention times of n-alkanes eluted under isothermal conditions versus their chain length is not a straight line, as generally accepted, even for n-alkanes of seventeen carbon atoms. Comparison of values of t'(R) deduced by methods based on the linearity assumption (ln t'(R)=mz+n) and on a different approach [t(R)=A+exp(B+Cz(D))] shows that experimental retention times do not fit the first expression, independently of the value used for the hold-up time, even if the correlation coefficient of the fit is better than 0.99999. (C) 1998 Elsevier Science B.V.