Separation of Phthalates in Nonaqueous Micelle Using Capillary Electrokinetic Chromatography

On the basis of nonaqueous capillary electrophoresis (NACE) and micellar electrokinetic chromatography (MEKC), a novel technique, nonaqueous micellar electrokinetic chromatography (NAMEKC), has been established. NAMEKC has the advantages of NACE and uses the separation mechanism of MEKC, showing special advantages for separation of hydrophobic compounds. Separation of three of the priority pollutants named by the US Environmental Protection Agency (EPA), i.e. dimethyl phthalate (DMP), diethyl phthalate (DEP), and dibutyl phthalate (DBP), was realized in 15 min by NAKEKC. Important factors on separation, such as the amount of water added in the electrophoretic running buffer, the acidity of water phase, organic additive, and the concentration of SDS, were investigated. The proportion of water in the electrophoretic running buffer could affect the current and the stability of SDS micelle. Organic additives and the acidity of water phase showed no effect on resolution. The concentration of SDS was a dominant factor, strongly affecting the partition of analytes in micelle. DMP, DEP, and DBP were separated in a short time under the optimized operation conditions using 20 mmol/L NaH2PO4 and 120 mmol/L SDS in formamide/water (9/1, v/v). The application of NAMEKC leads to successful separation of the three typical hydrophobic compounds, which provides a novel means to separate and analyze hydrophobic compounds.