Modeling interparticle and intraparticle (perfusive) electroosmotic flow in capillary electrochromatography

A model to estimate the extent of intraparticle, or perfusive, electroosmotic flow (EOF) in CEC capillaries packed with macroporous particles has been developed. Nucleosil packings (d(p) = 7 microm) having nominal pore sizes of 500, 1000, and 4000 A were studied. Intraparticle pores ranging from 50 to 10000 A in diameter were partitioned into 995 intervals of 10 A. Using pore size distribution data for the sorbents obtained by mercury intrusion porosimetry, fractions of the total column void volume contributed by pores in the range of interest were determined. The average channel diameter of the interstitial space was estimated from the d(p) of the packing; its fraction of total column volume was determined from the interstitial porosity. Estimations of relative EOF velocity in the intraparticle and interstitial channels were made by treating the channels as parallel cylindrical capillary tubes. Relative EOF values were combined with the volume fraction data and used as weighting factors in calculating an effective particle diameter (d(p,eff)) for each set of conditions (i.e., packing type, ionic strength of eluent). Values of d(p,eff) generated by the model correctly predict the trends observed in the experimental data. At the lowest ionic strength, plate height correlated inversely with the pore size of packing (h4000 A < h1000 A < h500 A). Rate curves for each column tended toward lower plate heights with increasing eluent ionic strength before converging at some limiting point. The point of convergence was reached at moderate ionic strengths for the larger pore media (1000 and 4000 A) and higher ionic strength for the 500 A.