Comparison of methods for extracting linear solvent strength gradient parameters from gradient chromatographic data

The linear solvent strength (LSS) theory of gradient elution is useful in the optimization of separations in high-performance liquid chromatography. While the fundamental parameters of this theory are defined in terms of isocratic behavior, gradient operation has been used previously to estimate those parameters to allow rapid optimization of the separation. In this study, various methods of extracting the LSS parameters from gradient retention data were examined. Sets of synthetic retention data were calculated directly from the equations of the LSS theory. When realistic experimental uncertainties were incorporated into these data sets, the LSS parameters used to generate the synthetic data were not recovered accurately unless special precautions were taken. For large molecules, an approximate LSS expression could be used to determine the solvent strength parameter with an error of less than 13%, which is comparable to or better than those for the other methods evaluated.