Reversed-phase liquid, micellar mobile

Quinones-Torrelo et al. (1999 2001) have demonstrated a correlation of pharmacokinetic properties with results from micellar liquid chromatography. In this method micellar solutions of nonionic surfactants are used as the mobile phase in reverse-phase liquid chromatography. Interactions between the mobile and stationary phases are purported to correspond to the membrane/water interface of biological barriers as hydrophobic, steric, and electronic interactions are important for both. For a series of 18 antihistamines Quinones-Torrelo et al. (2001) showed that both volume of distribution and half-life values were better correlated with retention on these columns than with the classical log K, w descriptor. 

Micellar Liquid Chromatography (MLC) uses surfactant solutions as mobile phases for reversed phase liquid chromatography. The two main properties of surfactant molecules, as related to chromatography, are micelle formation and adsorption at interfaces. The micelles play the role of the organic modifier, so their influence on retention has been extensively studied (1). At surfactant concentrations above the critical micellar concentration (CMC), micelles are present and the amount of free surfactant is essentially... 

The first report on the analytical use of an aqueous solution of a surfactant, above its critical micellar concentration (CMC), as mobile phase in reversed-phase liquid chromatography (RPLC) was published in 1980. The technique, named micellar liquid chromatography (MLC), is an interesting example of the modification of the chromatographic behavior taking advantage of secondary equilibria to vary both retention and selectivity. 

In the late 1970s, ionic surfactants were added for the first time to polar aqueous-organic mobile phases in reversed-phase liquid chromatography (RPLC) to form ion pairs (IPs). In IP chromatography, surfactant monomers adsorbed on a bonded silica-based stationary phase associate with neutral and ionic solutes, modifying their retention. The concentration of surfactant in the mobile phases is kept below the critical micellar concentration (CMC). In 1980, Daniel W. Armstrong reported the possibility of using... 

In addition to the factors listed in Table VIII, the nature of the surfactant-modified stationary phase affects P (partition coefficient for distribution of solute between bulk solvent and modified stationary phases) and thus will influence the retention observed. It should be realized that most of the normal and reversed-phase packing materials will adsorb/absorb surfactant molecules from the mobile phase solution and become coated to different degrees when surfactant mobile phases are passed through them. Numerous adsorption isotherms have been reported for various surfactant - stationary phase combinations illustrating this point (82,85,106,115-128,206). The presence of additives can mediate the amount of surfactant surface coverage obtained (110-129,175,206). It has been postulated that the architecture which adsorbed surfactant molecules can assume on conventional stationary phases can range from micellar, hemi-micellar, or admicellar to mono-,bi-, or multilayered, and/or other liquid crystalline-type structures (93,106,124,128,129,... 

Inositol phosphates isomers have also been separated by micellar mobile high-performance liquid chromatography (Brando et ah, 1990). This involved addition of the surfactant hexadecyltrimethylammonium hydroxide (HDTMA+OH ) to the mobile phase to form micellar ion association complexes that were separated on a reversed-phase column. Enhanced sensitivity and selectivity can be achieved by use of high-performance liquid chromatography in con-... 

Brando, C., Hoffman, T. and Bonvini, E. (1 990) High-performance liquid chromatographic separation of inositol phosphate isomers employing a reversed-phase column and a micellar mobile phase. Journal of Chromatography B 529, 65-80. 

To overcome this problem, our laboratories have initiated a program of study in the area of micellar liquid chromatography (MLC). The mobile phase in a MLC experiment consists of a surfactant that is at a concentration above the critical micellization concentration (cmc). We have learned that the addition of a co-surfactant to a micellar mobile phase will result in the formation of lamellar liquid crystals at the surface of the reversed phase (i.e., Cjg) material... 

Armstrong MJ, Carey MC (1982) The hydrophobic-hydrophilic balance of bUe salts. Inverse correlation between reverse-phase high performance liquid chromatographic mobilities and micellar cholesterol-solubilizing capacities. J Lipid Res 23, 70-80. 

Micellar liquid chromatography is the use of a surfactant such as sodium dodecyl sulfate (SDS) in the mobile phase at a concentration above the critical micelle concentration (CMC) of about 10 M. At the CMC, aggregation of60-100 surfactant monomers occurs with the hydrophobic part of the molecule oriented toward the center of the assembly and the hydrophilic tail exposed to the solution. Other surfactants used have been cationic or nonionic in nature, such as cetyltrimethylammonium ion and Brij-35, respectively. For reversed-phase HPLC, the surfactant can... 

Enormous advances and growth in the use of ordered media (that is, surfactant normal and reversed micelles, surfactant vesicles, and cyclodextrins) have occurred in the past decade, particularly in their chromatographic applications. New techniques developed in this field include micellar liquid chromatography, micellar-enhanced ultrafiltration, micellar electrokinetic capillary chromatography, and extraction of bioproducts with reversed micelles techniques previously developed include cyclodextrins as stationary and mobile-phase components in chromatography. The symposium upon which this book was based was the first major symposium devoted to this topic and was organized to present the current state of the art in this rapidly expanding field. 

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