Retention modeling in combined pH/organic solvent gradient reversed-phase HPLC

Abstract

An approach for retention modeling of double pH/organic solvent gradient data easily generated by automatically mixing two mobile phases with different pH and organic content according to a linear pump program is proposed. This approach is based on retention models arising from the evaluation of the retention data of a set of 17 OPA derivatives of amino acids obtained in 27 combined pH/organic solvent gradient runs performed between fixed initial pH/organic modifier values but different final ones and for different gradient duration. The derived general model is a ninth parameter equation easily manageable through a linear least-squares fitting but it requires eighteen initial pH/organic modifier gradient experiments for a satisfactory retention prediction in various double gradients of the same kind with those used in the fitting procedure. Two simplified versions of the general model, which were parameterized based on six only initial pH/organic modifier gradients, were also proposed, when one of the final double gradient conditions, pH or organic content was kept constant. The full and the simplified models allowed us to predict the experimental retention data in simultaneous pH/organic solvent double gradient mode very satisfactorily without the solution of the fundamental equation of gradient elution.

Chromatographic methods enabling the characterization of stationary phases and retention prediction in high‐performance liquid chromatography and supercritical fluid chromatography

“…Polynomial and rational function models represent the most frequently utilized empiric retention models . The popularity of the polynomials consists in their simple form and well‐known properties.…”

“…Apart from simple polynomial and rational function empirical models there are also other alternative empirical approaches described in the literature .…”

Artificial Neural Network Prediction of Retention of Amino Acids in Reversed-Phase HPLC under Application of Linear Organic Modifier Gradients and/or pH Gradients

“…Many attempts to describe the retention of solutes in RP-HPLC under the application of mobile-phase gradients are based on the solution of the fundamental equation of gradient elution [12,13,14,15,16], ∫0tnormalR−t0dtt0normalk=1 where t R is the retention time, t 0 is the column hold-up time, and k is the retention factor. Analytical or numerical solutions of Equation (1) require the dependence of k upon the mobile-phase composition.…”

“…This approach was here extended to the RP-HPLC retention of ionizable solutes of biological relevance, such as amino acids, analyzed under the application of linear φ gradients, pH gradients, or combined φ/pH gradients, whereby the target compounds were previously derivatized with o -phthalaldehyde (OPA) to allow their fluorescence detection. The data investigated in the present study were taken from three works of Pappa-Louisi and co-workers [14,15,16], who collected the experimental data and developed retention models based on the solution of the fundamental equation of gradient elution to verify the accuracy of the predicted retention by different equations or fitting algorithms.…”

Response surface methodology based on central composite design accompanied by multivariate curve resolution to model gradient hydrophilic interaction liquid chromatography: Prediction of separation for five major opium alkaloids

“…Reduction of needed gradient parameters permits to add two more factors: concentration of buffer and its pH. Although some studies with changing one factor at a time (OFAT), to avoid interaction effects between φ and pH keep φ constant and vary pH or conversely but a real gradient analysis concludes simultaneous varying pH and φ, commonly without effort to keep one of them constant . Furthermore when we are using CCD‐RSM finding interaction effects are targeted that is its advantage relative to OFAT procedure.…”