Theoretical investigation of the spatial progression of temporal statistical moments in linear chromatography

Migration and dispersion in chromatography are modeled by analogy to an eff ective eddy diffusion process, On the basis of this model, the spatial rate s of temporal statistical moment change are derived for general chromatogra phy in linear media, In most practical cases, these equations can be simpli fied so that temporal statistical moments can be calculated by solving a sy stem of ordinary differential equations that depend only on the local HETP, solute velocity, and initial values of the temporal statistical moments. T he calculations of temporal centroid, temporal variance, temporal skew, and temporal excess are demonstrated for the case of linear solvent strength g radients. It is shown for the case of temporally invariant separation envir onments, such as isocratic liquid chromatographic systems and isothermal ga s chromatographic systems, that temporal variance contributions are spatial ly additive and that the temporal third normalized central moment is unaffe cted by spatial variations in the medium. A refined explanation is given fo r how peak symmetry is improved in gradient forms of chromatography.