Micellar liquid chromatography stationary phase

Lantz, A.W., Pino, V., Anderson, J.L., and Armstrong, D.W., Determination of solute partition behavior with room-temperature ionic liquid based micellar gas-liquid chromatography stationary phases using the pseudophase model, /. Chromatogr. A, 1115, 217-224, 2006. 

Mass-action model of surfactant micelle formation was used for development of the conceptual retention model in micellar liquid chromatography. The retention model is based upon the analysis of changing of the sorbat microenvironment in going from mobile phase (micellar surfactant solution, containing organic solvent-modifier) to stationary phase (the surfactant covered surface of the alkyl bonded silica gel) according to equation ... 

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. 

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. 

Stationary Phase in Micellar Liquid Chromatography Surfactant Adsorption and Interaction with Ionic Solutes... 

Berthod, A. and Roussel, A. 1988. The role of the stationary phase in micellar liquid chromatography, J. Chromatog., 449 349-360. 

However, experimental values for log P are sometimes difficult to obtain. Recently, we have investigated the utility of micellar liquid chromatography for assessing the lipophilic character of organic molecules in biological media. In our study we used a liquid crystalline stationary phase to generate retention data for a set of 22 mono-, di-, and tri-substi-tuted benzenes. The retention factor (i.e., log k ) of these compounds was found to be correlated to the log of their octanol/water partition coefficient. 

These studies suggest that micellar liquid chromatography with lamellar stationary phases may yield a useful hydrophobic parameter. In view of the fact that retention times (and hence log k values) can be determined with high precision for impure, unstable, and even volatile compounds, we conclude that log k values obtained with lamellar phases may provide useful estimates for log P. 

A. Berthod, I. Girard and C. Gonnet, Micellar Liquid Chromatography, Adsorption Isotherms of Two Ionic Surfactants on Five Stationary Phases, Anal. Chem., 58 1356 (1986). 

The two main properties of surfactant molecules are micelle formation and adsorption at interfaces. In Micellar Liquid Chromatography (MLC), the micelle formation property is linked to the mobile phase. Micelles play the role of the organic modifier in RPLC. Nonpolar solutes partition themselves between the micelle apolar core and the apolar bonded stationary phase. This partitioning will be the subject of Chapter 5. The surfactant adsorption property is linked to the stationary phase. A significant number of surfactant molecules may adsorb on the stationary phase surface changing its properties. The study of such adsorption and its associated problems is the main subject of this chapter. 

Borgerding MF, Hinze WL, Stafford LD, Fulp GW Jr, and Hamlin WC Jr (1989) Investigation of stationary phase modification by the mobile phase surfactant in micellar liquid chromatography. Analytical Chemistry 61 1353-1358. 

Alain Berthod received his PhD in 1979 from the University of Lyon. He took an assistant professor s position at the French National Center for Scientific Research (CNRS) working in electrochemistry. In 1983 he was promoted as associate professor and in 1993 as research director. He focused on the developing and the use of micellar solutions and microemulsions in chromatography. His interests lie in the separation of chiral molecules and enantiorecognition mechanisms. He has contributed to the development of the countercurrent chromatography technique that uses a sup-port-free liquid stationary phase. He was member of the editorial board of major analytical chemistry and chromatography journals. He is editor-in-chief of Separation Purification Reviews (Taylor Francis, Philadelphia, Pennsylvania). 

Gel Filtration. Micellar solutions have also been utilized in gel permeation (filtration) chromatography ( ] ). In fact, the first example of a separation which used a micellar mobile phase was in this area of exclusion liquid chromatography (ELC) ( 86). The last six entries in Table XI summarize some of the separations/work reported concerning micellar mobile phases in ELC. In most of these applications, the work was conducted with stationary phases of relatively small pore size. With these type phases, the relatively large micellar aggregates are confined to the excluded volume of the column and elute rapidly whereas smaller solute molecules in a mixture... 

The stationary phases play an important part in Liquid Chromatography using micellar mobile phases. They interact with both the surfactant and with solutes. To study the interactions with surfactants, adsorption isotherms were determined with two ionic surfactants on five stationary phases an unbonded silica and four monomeric bonded ones. It seems that the surfactant adsorption closely approaches the bonded monolayer (4.5 pmol/m2) whatever the bonded stationary phase-polarity or that of the surfactant. The interaction of the stationary phase and solutes of various polarity has been studied by using the K values of the Armstrong model. The KgW value is the partition coefficient of a solute between the... 

Electrokinetic chromatography is conducted in capillary tubes and mobility is generated by the application of electrical potential but separation arises as a result of interactions with a micellar stationary phase formed by surfactants added to the mobile phase. Therefore electrokinetic chromatography contains elements of both liquid chromatography and capillary electrophoresis. 

The phenomena just described are quite similar to what occurs in a liquid partition chromatographic column except that the stationary phase is moving along the length of the column at a much slower rate than the mobile phase. The mechanism of separations is identical in the two cases and depends on differences in distribution constants for analytes between the mobile aqueous phase the hydrocarbon pseudostationary phase. The process is thus true chromatography hence, the name micellar electrokinetic capillary chromatography. Figure 33-15 illustrates two typical separations by MECC. 

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... 

Gel electrophoresis (GE) was developed in the 1940s, while capillary electrophoresis appeared 40 years later. Then chromatography with electric potential-driven liquid flow also developed into micellar electroldnetic chromatography (MEKC) and electrochromatography (EC), both with capillary columns. Electrophoresis, thus, is not a chromatographic technique, since there is no stationary phase, except in MEKC and EC. 

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