Subtraction Model to Characterize Non-Polar Stationary Phases in Supercritical Fluid Chromatography

In a recent study published in Journal of Chromatography A, researchers from East China University of Science and Technology tested the feasibility of a novel subtraction model to characterize non-polar stationary phases in supercritical fluid chromatography (SFC) (1). For this study, the research team focused on C4, C8, and phenyl-type columns (1).

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The researchers compared the results of the model to the linear solvation energy relationship (LSER) model. The LSER model has been traditionally used for this application, but it contains several key limitations. The model’s predictive capabilities of the LSER model are not as accurate as many chromatographers would like it to be (1).

The researchers started off by conducting routine column characterization using the established LSER model. Subsequently, they presented the subtraction model comprising six terms: log α = η'H + θ'P + β'A + α'B + κ'C + σ'S. Notably, the θ'P term, representing dipole or induced dipole interactions, was deliberately integrated into the formula, emphasizing its importance in SFC (1).

For data processing, the process involved a bidirectional fitting approach in the first six steps, with all parameters except for σ'S calculated based on the equation: log α = log (ki/kref) ≈ η'H + θ'P + β'A + α'B + κ'C (1). In the seventh step, residual analysis was employed to describe the σ'S term using the equation: σ'S = log α_exp. - log α_pre. This comprehensive modeling procedure was instrumental in achieving a more accurate representation of the non-polar stationary phases in SFC (1).

The researchers validated the subtraction model by using 12 compounds of unknown retention characteristics and six columns not part of the modeling process (1). The results demonstrated accurate predictions of log k, as indicated by the adjusted determination coefficient (R²_adj), which ranged from 0.9927 to 0.9998 for columns and from 0.9940 to 0.9999 for compounds, respectively (1). This validation underscored the effectiveness of the subtraction model in characterizing non-polar stationary phases.

This study proposes a new subtraction model (log α = η'H + θ'P + β'A + α'B + κ'C + σ'S) for characterizing non-polar stationary phases. In developing this new model, the research team focused on dipole interaction and supplemented impedance with residual analysis (1). By demonstrating the feasibility of their subtraction model in SFC, the research team advances the field of SFC and our understanding of non-polar stationary phases.

Reference

(1) Jiang, D.; Yang, J.; Chen, Y.; Jin, Y.; Fu, Q.; Ke, Y.; Liang, X. An attempt to apply a subtraction model for characterization of non-polar stationary phase in supercritical fluid chromatography. J. Chromatogr. A. 2023, 1701, 464071. DOI: 10.1016/j.chroma.2023.464071