Influence of deactivating method of the inner glass capillars surface on the aniline derivatives retention indices

Abstract

The article deals with the study of retention indices of aniline derivatives which were measured on glass capillary columns with different ways of deactivating the inner surface of the capillary. One of the columns was prepared by deactivating the inner surface of the glass capillary by the method of silanization. The other column was deactivated by forming an unextractable polyethylene glycol layer. Then, the same apolar stationary phase of methylsiloxane OV-101 was applied to both capillaries. It is shown that the deactivation of the glass capillary by an unextractable layer of polyethylene glycol significantly affects the chromatographic properties of the apolar stationary phase. This effect leads to the appearance of an intercolumnal difference in the retention indices of aniline derivatives. It was found that the value of the inter-column difference in the retention indices is not constant. It was shown that alkyl substituents perform a screening function during the interaction of alkylaniline molecules with a stationary phase. Therefore, an increase in the size and number of alkyl groups in alkylaniline molecules leads to a decrease in the difference between their retention indices on the columns with different deactivation methods. Non-alkyl substituents cause an increase in the polarization of molecules of aniline derivatives. As a result, aniline derivatives with non-alkyl substituents are more strongly retained on a column deactivated by polar polyethylene glycol. In this case, increasing the size of the substituent leads to an increase in the inter-column difference in the retention indices. Large values of the intercolumn difference in retention indices measured on columns with different methods of treating the surface of capillaries exclude their direct use for identification purposes. Correlative and predictive possibilities of intercolumn (interlaboratory) recalculation of retention indices of alkylanilines measured on the same stationary phase, but with different ways of treating the inner surface of capillary columns, were investigated. With the use of the entire set of N-, N,N- and С-alkylanilines, a correlation has been obtained that has a low correlation level (standard deviation of 7.2 i.u.). The use of only narrow homologous series as base compounds made it possible to significantly improve the correlation capabilities of intercolumn (interlaboratory) conversion of the retention indices of alkylanilines. The obtained equations were used to estimate the accuracy of the predictive calculation of the retention indices of the nearest homolog of the base series of compounds, as well as representatives of other homologous series. The accuracy of the calculations was estimated as the difference between the calculated and experimental values of the retention indices. It is established that the retention indices of the nearest homologue are determined with acceptable accuracy. However, for representatives of other homologous series, the calculation error considerably exceeds the value of the generally accepted criterion of identification accuracy. Consequently, intercolumn (interlaboratory) recalculation of retention indices of alkylanilines measured on columns with different methods of surface treatment of capillaries for identification purposes is possible only within narrow homologous series.