Modelling of solute retention in the reversed-phase high-performance liquid chromatography system with the chemically bonded 3-cyanopropyl stationaryphase

We investigated the applicability of three models of solute retention (devi sed by Snyder et al., Schoenmakers et al., and Kowalska) for reversed-phase high-performance liquid chromatography (RP-HPLC) for description of the ch romatographic behaviour of 25 lest solutes in the RP-HPLC systems with the 3-cyanopropyl stationary phase and the methanol + water eluent. The employe d test solutes considerably differed with respect to molecular structure, a s they belonged to chemical classes of (i) benzene and alkylbenzenes, (ii) hydroxyaromatics, and (iii) crown ethers. In the case of the chemically bon ded stationary phases, the 3-cyanopropyl phase included, one encounters the mixed mechanism of solute retention with the contributory effects of parti tion and adsorption. From our investigations, it comes out that the retenti on model proposed by Schoenmakers et al. (i.e., model II) is the best suite d for description of the chromatographic behaviour of solutes on such packi ngs, while the remaining two models (i.e., models I and III) perform less a ccurately. An additional investigation was performed with aid of the relati onship between the retention parameters (i.e., log k) of the employed test solutes and the logarithms of their partition coefficients (log P) in the o ctanol/water system (as calculated from the hydrophobic fragmental constant s after Rekker), depending on the quantitative composition of the binary el uent. The greater is the deviation of the log k vs. log P relationship from linearity (as monitored by the decreasing values of the respective linear correlation coefficients, r), the less pronounced becomes the contribution of partition and hence the importance of adsorption for the overall retenti on increases. Thus, the log k vs. log P study was performed in order to fol low the partition <-> adsorption balance with the changing volume proportio ns of methanol in the mixed eluent, and ultimately to link an extent of con tamination of the nominal reversed-phase partition mechanism by adsorption with the predictive power of models I-III. Finally, an effort was undertake n aimed at demonstration of a considerably enhanced performance of model II I, when applied to the experimental conditions that corresponds better with the theoretical assumptions of this approach. (C) 1999 Elsevier Science B. V. All rights reserved.