Enhancements in micellar electrokinetic chromatographic separations with decanonyl-N-methylalkanamide micelles through the addition of alkyl sulfates

Abstract

Sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS) are effective additives for improving the efficiency of the micellar electrokinetic chromatography (MEKC) with micelle forming solutions of decanonyl-N-methylglucamide (MEGA 10) with boric acid, pH 10. MEGA 10, a nonionic surfactant, is one of a series of micelle forming compounds for which the surface charge density of the micelle and electrophoretic migration behavior can be varied through the extent of complexation with a charged species, i.e., borate or boronate ions. Using aniline and a series of 11 substituted anilines as model solutes, the addition of 0–10 m M concentrations of SDS or 0–8 m M STS to buffers containing 20 m M or 40 m M MEGA 10 and boric acid (1:4 concentration ratio) results in an increase in the solute capacity factors and an improvement in separation efficiencies with only small changes in the rate of electroosmotic flow and size of the elution range. Further addition of the sodium alkyl sulfate surfactants results in a large expansion of the elution range. The effects of SDS and STS are attributed to changes in the structure of the MEGA 10/borate micelles resulting in a mixed surfactant micelle structure which is more permeable for the solutes.