Influence of the pre-elution of solute in initial mobile phase on retention time and peak compression under linear gradient elution.

Under gradient elution the solute will firstly migrate in initial mobile phase due to dwelling time (t) of the system. The pre-elution of solute in initial mobile phase can be accounted for by a dimensionless value of t/(tk), where t and k denote dead time and retention factor in initial mobile phase, respectively. The influence of t/(tk) on retention time (t) and peak compression factor (G) are discussed under linear gradient elution. A general expression for G is proposed, and two analytical forms of it which are suited for linear solvent strength model (LSSM) and quadratic solvent strength model (QSSM) respectively are presented. The well-known Poppe equation for G which is derived under LSSM is extended by taking t/(tk) into account. The expression for G under QSSM takes into account the curvature in the plot of logarithmic retention factor vs. mobile phase composition. By taking twelve compounds degraded from lignin as analytes, the experimental and predicted chromatograms are found to be well consistent. It is shown that t/(tk) has more effects on the prediction of t than that of G.