Overload behavior and apparent efficiencies in chromatography

Over the last 50 years, many analysts have attempted to analyze column overloading by measuring the drop of the column HETP with increasing sample size and to predict elution band profiles from overloaded columns by combining the influences of the thermodynamic overloading and of axial dispersion, using a simplistic perturbation model. This approach violates the principle of mass conservation. The results of the predictions do not agree with those of exact calculations made with the equilibrium-dispersive (ED) model of chromatography for constant axial dispersion. The plots of the reduced apparent column efficiency N/N-kin, versus the injected concentration, log C-0. or the injected mass, log me, may provide useful information only regarding the onset of overloading of any particular column but they are meaningless to compare the overloading behavior of columns packed with different packing materials, unless the columns used satisfy impractical requirements (same efficiency, same retention factors, and sample sizes used proportional to the volume of stationary phase in the column). (c) 2012 Elsevier B.V. All rights reserved.