Anomalies of temperature dependence of gaschromatographic retention indices (review of literature)

Abstract

The influence of temperature (T) of gas chromatographic separation on variations of isothermal retention indices (RI) and the possibility of using temperature coefficients of retention indices β = dRI/dT for identification of analytes is considered in the review. Features of linear and nonlinear approximations of RI(T) dependencies is considered on the example of compounds of different chemical origin and stationary phases of different polarities. Of special interest are the anomalous dependences of RI(T) with extrema which are observed for some polar analytes on nonpolar phases. This anomaly, first discovered in 1990s — beginning of 2000s, implies the variations in the signs of temperature coefficients β which leads to appearance of minima or maxima on the plots of the RI(T) dependences. Concepts of the entropy index, first and second derivatives of the retention indices proposed to explain the anomalies of dependencies RI(T) are discussed. Despite general acceptance for a long time that only the chemical nature of the analyte and the type of stationary phase determine the character of the RI(T) dependence, effect of injected amount of polar analyte on the character of RI(T) dependences was recently revealed. It is shown that these anomalous temperature effects are caused by the dynamic modification of nonpolar phase by polar analyte. Refs 125. Figs 6.