Prediction of retention in reversed-phase liquid chromatography by means of the polarity parameter model.

The polarity parameter model previously developed: log k=(log k)(0) + p(P(m)(N) - P(s)(N)) has been successfully applied to study several chromatographic systems involving new generation RPLC columns (Luna C18, Resolve C18, XTerra MSC18, and XTerra RP18). In this model the retention of the solutes (log k) is related to a solute parameter (p), a mobile phase parameter (P(m)(N)) and two chromatographic system parameters [P(s)(N) and (log k)(0)]. The studied systems have been characterized with different acetonitrile-water and methanol-water mobile phases, using a set of 12 neutral solutes of different chemical nature. The polarity parameter model allows prediction of retention of any solute in any mobile phase composition just using the retention data obtained in one percentage of organic modifier and the polarity parameters established in the characterization of the chromatographic systems. This model also allows the solute polarity data transference between RPLC characterized systems, so it is possible to predict the retention in various RPLC systems working experimentally with just one of them. Moreover, the global solvation parameter model has also been applied to the same chromatographic systems using a wide set of solutes in order to compare its predictive ability with the one of the polarity parameter model. The results clearly show that both models predict retention with very similar accuracy but the polarity parameter model requires much less preliminary experimental measurements to achieve equivalent results than the global solvation approach.

Application of a polarity parameter model to the separation of fat-soluble vitamins by reversed-phase HPLC.

The retention behavior of a series of fat-soluble vitamins has been established on the basis of a polarity retention model: log k = (log k)(0) + p (P(m) (N) - P(s) (N)), with p being the polarity of the solute, P(m) (N) the mobile phase polarity, and (log k)(0) and P(m) (N) two parameters for the characterization of the stationary phase. To estimate the p-values of solutes, two approaches have been considered. The first one is based on the application of a QSPR model, derived from the molecular structure of solutes and their log P(o/w), while in the second one, the p-values are obtained from several experimental measurements. The quality of prediction of both approaches has also been evaluated, with the second one giving more accurate results for the most lipophilic vitamins. This model allows establishing the best conditions to separate and determine simultaneously some fat-soluble vitamins in dairy foods.

Polarity parameters of the Symmetry C18 and Chromolith Performance RP-18 monolithic chromatographic columns.

A set of 12 compounds of different chemical nature has been established to characterise RPLC columns on the basis of a polarity retention model previously developed: log k=(log k)(0)+p(P(m)(N)-P(s)(N)). This model allows the calculation of the retention factor (k) of any non-ionized compound using one parameter which describes the polarity of the solute (p), another one for the polarity of the mobile phase (P(m)(N)) and two more parameters for the characterisation of the stationary phase ((log k)(0) and P(s)(N)). The selected set of compounds allows the determination of (log k)(0) and P(s)(N) of stationary phases and it has been used to characterise two commercial columns (Symmetry C18 from Waters and Chromolith Performance RP-18 monolithic from Merck). Column parameters, together with those of the mobile phase permit successful transfer of retention data between chromatographic systems. Prediction of retention of a variety of non-ionized analytes has been also successfully achieved using the column descriptors and p values of solutes from a previously established p data base.