Description of chromatographic performance in reversed-phase liquid chromatography based on a generalised model. Part I: Column characterisation.

Liquid chromatography has advanced considerably since its introduction in the 1970s, with reversed-phase liquid chromatography (RPLC) becoming the dominant technique for separating non-volatile molecules. A key strategy for optimising separation conditions is the modelling of chromatographic retention from experimental data. Traditionally, this is achieved by fitting model parameters for each solute, resulting in individual solute models (ISMs). More recently, we have developed and validated a generalised (global) model (GEM), which have proven particularly useful for method development, especially when handling complex samples. In GEM, the chromatographic behaviour of a set of solutes is fitted simultaneously, generating both system-related model parameters (reflecting common solute interactions with the stationary and mobile phases) and solute-specific parameters, such as log k0,i (the extrapolated retention factor of each solute i at zero organic solvent). In this work, stationary phases with distinct chemistries, including octadecylsilane, butylsilane, phenylsilane, and cyanosilane, were characterised using both ISMs and GEMs. Retention data were obtained for a set of 15 sulphonamides, with octanol-water partition coefficients (log Po/w) ranging from ‒1.0 to +1.7), under both isocratic and gradient conditions. GEM demonstrated predictive accuracy comparable to ISMs, with standard errors of prediction for retention times of 0.09‒0.14 and 0.35‒0.42 min for isocratic elution, and 0.04‒0.32 and 0.27‒0.42 min for gradient elution, for ISMs and GEMs, respectively. In addition, GEM provided consistent log k0,i values, which showed a strong correlation with both retention times and log Po/w, in contrast to ISMs. The alignment between GEM system parameters and the characteristics of the studied stationary phases further highlights the robustness and broad applicability of this approach.