INFLUENCE OF COUNTER PRESSURE ON SEPARATION PERFORMANCE IN SDS-MEKC

The influence of a hydrostatic counter pressure on basic mobility equa tions in MEKC was analyzed theoretically and investigated experimental ly, Taking into account the influence of counter pressure, the modifie d mobility equations predict a decreased migration time ratio t(0)/t(M C), which was confirmed by results obtained in SDS-MEKC separation of a homologous series of n-alkyl phenyl ketones. As a result, the migrat ion time window could be enlarged in a simple way without having to ch ange the chemistry of the system, Although counter pressures reduce pe ak efficiency in MEKC by disturbing the plug profile, the concomitant enlargement of the migration time window compensates for this effect. Especially for later migrating compounds, peak resolution could be enh anced at moderate counter pressures. The overall peak capacities withi n the whole migration window increases slightly when applying counter pressures up to 10 mbar.