Background and operating parameters in microemulsion electrokinetic chromatography

Abstract

Microemulsion electrokinetic chromatography (MEEKC) is an electrodriven separation technique. Separations are generally achieved using microemulsions consisting of surfactant-coated nanometer-sized oil droplets suspended in aqueous buffer. A cosurfactant such as a short-chain alcohol is generally used to stabilize the microemulsion. This review summarizes the various microemulsion types and compositions that have been used in MEEKC. The effects of key-operating variables such as surfactant type and concentration, cosurfactant type and concentration, buffer pH and type, oil type and concentration, use of organic solvent and cyclodextrin additions, and temperature are described. Specific examples of water-in-oil microemulsions and chirally selective separations are also covered.

MEKC: An update focusing on practical aspects

“…Microemulsion electrokinetic chromatography (MEEKC) [18,19], which can be regarded as an extension of MEKC, was not dealt with in the previous review; however, it has grown so fast and extensively in recent years that it warrants separate discussion and has thus also been excluded from this review. On the other hand, MEKC on microchips has fully met the expectations anticipated in the previous review.…”

(S)-(+)-2-Octanol as a Chiral Oil Core for the Microemulsion Electrokinetic Chromatographic Separation of Chiral Basic Drugs

“…MEEKC has several optimization advantages over other techniques in terms of selectivity, 11 elution range and composition. 12,13 Unique opportunities exist to fine-tune the microemulsion characteristics by changing the identity and concentration of its components in addition to the usual areas for modification (pH, buffer identity and concentration). 14 In MEEKC, the elution range can be altered by increasing or decreasing the charge density of the aggregate via the surfactant concentration.…”

Investigation of solvent effects in capillary electrophoresis for the separation of biological porphyrin methyl esters

“…Indeed, MEEKC has been recently demonstrated to be highly useful for the separation of a diverse group of highly hydrophobic substances, such as b-diketones [28], polyaromatic hydrocarbons [29], steroids [30], polymer additives [31], fatty acids [32], biphenyl nitrile compounds [33], diphenylhydrazones of dicarbonyl sugars [34], lipid-soluble vitamins [35], and hematoporphyrin mixtures [36]. Note that in order to achieve optimal separation of various hydrophobic compounds, the addition of an organic modifier (i.e., a so-called second cosurfactant, such as 2-proponal) into the running buffer is at times often necessary [25][26][27].…”

“…The ability to enhance the solubility of hydrophobic compounds in the running buffers by incorporating a waterimmiscible oil phase in the micellar structure (i.e., the formation of relatively large, nanometer-sized microemulsion droplets) is one of the major advantages of employing MEEKC in CE separations [25][26][27]. Indeed, MEEKC has been recently demonstrated to be highly useful for the separation of a diverse group of highly hydrophobic substances, such as b-diketones [28], polyaromatic hydrocarbons [29], steroids [30], polymer additives [31], fatty acids [32], biphenyl nitrile compounds [33], diphenylhydrazones of dicarbonyl sugars [34], lipid-soluble vitamins [35], and hematoporphyrin mixtures [36].…”