Peak parking-moment analysis. A strategy for the study of the mass-transfer kinetics in the stationary phase.

The combination of peak parking and moment analysis is proved to be a powerful strategy for studying the molecular diffusivity of solute molecules in stationary phases and for determining the corresponding kinetic parameters. The physical meaning of the traditional kinetic parameter, gammasDs, the diffusion coefficient of solute molecules in stationary phases, is first clarified. A second kinetic parameter, DLs, is then derived from gammasDs, and the correspondence between DLs and the surface diffusion coefficient, Dsur, is discussed. Then, the results of peak parking experiments carried out with RPLC systems using aqueous methanol solutions and C18-silica columns are reported. The moments of pulse responses were measured and are analyzed. The values and some characteristics of DLs measured by the peak parking-moment analysis method are compared with those of Dsur determined using the pulse response-moment analysis method. The comparison of the numerical values of DLs and Dsur suggests that DLs is nearly equal to Dsur and that it exhibits the same dependence on the retention strength as does Dsur with regard to the mass-transfer kinetics and extrathermodynamics. This comparison allows us to conclude that DLs corresponds to Dsur. The advantages and disadvantages of the peak parking-moment analysis method were compared with those of the pulse response-moment analysis method. The combination of these two methods provides a comprehensive strategy for measuring the mass-transfer kinetics in the stationary phase.