Effects of pH on electrokinetic velocities in micellar electrokinetic chromatography

Effects of pH of micellar solutions on electrokinetic velocities in micellar electrokinetic chromatography were investigated using sodium dodecyl sulfate (SDS) solutions. The electroosmotic velocity decreased with a decrease in pH below 5.5, while the electrophoretic velocity of the SDS micelle was almost constant throughout the pH range of 7.0–3.0. Consequently, the migration velocity of the SDS micelle decreased with a decrease in pH, and its direction changed at pH 5.0: the direction was the same as that of the electroosmotic velocity above pH 5.0 and the reverse below pH 5.0. In the latter case, the retention time and resolution will be infinity at a relevant value of the capacity factor, and a wider elution range can be attained.