Effects of organic mobile phase modifiers in micellar electrokinetic capillary chromatography

The addition of 1–20% (v/v) of methanol or acetonitrile as organic modifier to the mobile phase in a micellar electrokinetic capillary chromatographic (MECC) system, containing sodium dodecyl sulfate and a buffer, is shown to extend the elution range and thus increase the peak capacity of a given system. Although the net change in the elution range parameter, t_o/t_mc, is essentially the same for both modifiers, the acetonitrile-modified system exhibits much faster elution times for the polar and non-polar test solutes employed in this study. Retention, as measured by the capacity factor, is generally decreased with the increase of an organic modifier, just as in conventional reversed phase chromatography. However, changes in selectivity as a function of the added modifiers are noted among polar and non-polar solutes as well. The efficiency of these MECC systems is increased with the addition of either organic modifier.