In size-exclusion electrochromatography (SEEC) there exists an optimum in p
ore-to-interstitial flow ratio with respect to the resolution. Two methods
for finding and controlling the optimal pore-to-interstitial flow ratio in
SEEC have been studied: (i) varying the ionic strength of the mobile phase
and (ii) the application of a hydrodynamic flow in addition to the electrco
-driven flow. Both methodologies have been evaluated in terms of efficiency
and applicability with columns packed with silica particles containing por
es of either 10 or 50 nm in diameter, and with different ionic strength mob
ile phases. Using the first method with the 10-nm pore particles, the how r
atio could be adjusted within an appropriate range. However, with the wide-
pore (50 nm) particles it appeared that the pore-to-interstitial flow ratio
was too high at all conditions tested to obtain proper selectivity. In the
second approach, the desired pore flow was generated by the electric field
and the pore-to-interstitial flow ratio could then be adjusted by an appli
ed pressure over the column. This method was applicable with both particle
types studied. The application of a (low) voltage gradient in addition to a
pressure-driven flow resulted in a sharply improved separation efficiency
as a result of a strongly improved mass transfer due to intra-particle elec
troosmotic flow. When optimized, pressurized SEEC generates identical separ
ation efficiencies for polystyrene standards as are obtained with pure SEEC
, while the reduction in selectivity, in comparison to pressure-driven SEC,
is kept minimal. (C) 2001 Elsevier Science B.V. All rights reserved.