Gas-Chromatographic Retention Indices in Dependence on the Ratio of Analytes to Reference Components

One of the main factors determining the interlaboratory reproducibility of gas-chromatographic retention indices is their linear dependence on the logarithms of the ratios of the amounts of analytes and reference components, which is rarely taken into account. It is found that the effect of this factor is much stronger for packed columns in comparison to that for more efficient capillary columns; it decreases with the sample dilution and with the increase in the temperature of gas-chromatographic separation. It was shown that the effect of relative amounts of components on their retention indices agrees with the main principles of the chromatographic plate theory and is associated with neither the overloading of chromatographic columns nor the nonlinearity of the adsorption isotherms. To improve the reproducibility of indices, it is recommended to use retention parameters measured at certain points in the front edges of the chromatographic peaks corresponding to similar intensities of the analytical signal rather than at the peak maxima.