Peak Compression in Gradient Elution Liquid Chromatography

Abstract

The equation for apparent plate height under gradient elution which ignores the sorption of mobile phase solvents on the stationary phase is presented. This equation is suited for any kind of solvent strength, gradient profile, and the variation in plate height (H) with mobile phase composition (φ). Based on the equation, the expressions for peak compression factor (G) are derived by assuming constant and varied column efficiency, respectively. In the case of linear gradient and constant column efficiency, analytical expressions for G are derived by assuming the linear solvent strength model (LSSM) and quadratic solvent strength model (QSSM), respectively. In the case of QSSM, the influence of the curvature in the plot of logarithmic retention factor (lnk) vs. φ on G is taken into account. The peak compression under an ideal situation (H = 0) is also discussed. When a narrow injection is conducted, the ideal peak compression factor (G ideal), which is defined as the ratio of the band width at beginning to that at elution, is equal to k φ 0 / k φR , k φ 0 and k φR denoting the retention factors at the beginning and at elution, respectively. It is shown that the expression for G obtained under a real situation (H > 0) can be expressed as the function of G ideal.