Determination of the interparticle void volume in packed beds via intraparticle Donnan exclusion

Fast, accurate, and convenient analysis of bed densities for columns packed with fine reversed‐phase particles

“…Contrary to our previous experience with packings of fine (3 μm) particles, for which we observed a continuous decrease of nitrate elution volumes even at low buffer concentrations due to interparticle EDL overlap 14, the electrostatic exclusion curve for the 1.8 μm ZORBAX Eclipse Plus C 18 column displays a clearly defined plateau region at low buffer concentrations from which the column's interparticle porosity is easily determined as ε inter =0.375 (Fig. 1).…”

“…We recently developed a method based on Donnan (electrostatic) exclusion of a small, unretained inorganic ion from the intraparticle pore space to determine V inter and ε inter of particle‐packed HPLC columns 14. Our approach is faster, far simpler, and at least as accurate as the established methods.…”

“…Surface charge density and r meso are the properties of the packing material, whereas λ D depends on the mobile phase, namely its solvent composition and ionic strength. Variation of the mobile phase ionic strength manipulates the ratio r meso /λ D and thus the accessible void volume for a small, nonretained, co‐ionic tracer: from complete permeation of the packing's void volume (ε tracer =ε total ) for r meso >>λ D to complete exclusion of the tracer from the intraparticle pores (ε tracer =ε inter ) at r pore ≈λ D , over a broad intermediate range, where the tracer has partial access to the intraparticle pore space 14.…”

“…In our previous study 14, we used in‐house‐packed capillary columns and determined ε inter for a variety of packing materials (with different surface chemistry and mean particle as well as mean intraparticle pore size), analyzing the influence of r meso and the surface charge density on the onset of Donnan exclusion. In this study, we extend the Donnan‐exclusion method to determine the interparticle porosity ε inter of commercially available analytical HPLC columns packed with fine reversed‐phase particles of different nominal sizes (1.8, 2.7, 3.5, and 5 μm) and construction (fully porous and core‐shell).…”

Use of pressure drop profiles to assess the accuracy of Total Pore Blocking measurements of the external porosity of chromatographic columns

“…Detection problems do not occur in the TPB method since the repulsion of the t 0 -marker is based on the fact that it cannot enter the mesopores due to the presence of the blocking agent. Additional potential error sources of the Donnan exclusion are the fact that the exclusion of the marker can already occur in the interstitial space itself and that the pores of the particles can be so large that complete electrostatic repulsion is difficult to realize [14]. The TPB method, in contrary, is valid for the measure-0021-9673/$ -see front matter © 2011 Elsevier B.V. All rights reserved.…”