Micellar chromatography

Another relatively new lipophilicity scale proposed for use in ADME studies is based on MEKC [106]. A further variant is called BMC and uses mobile phases of Brij35 [polyoxyethylene(23)lauryl ether] [129]. Similarly, the retention factors of 16 P-blockers obtained with micellar chromatography with sodium dodecyl sulfate as micelle-forming agent correlates well with permeability coefficients in Caco-2 monolayers and apparent permeability coefficients in rat intestinal segments [130]. 

M. J., Biopartitioning micellar chromatography an in vitro technique for predicting human drug absorption, J. Chromatogr. B 2001, 753, 225-236. 

Environmental Tin Chlorides of dimethyltin, trimethyltin, dibutyltin and tributyltin diphenyltin and triphenyltin Micellar chromatography 24-51 pg as Sn Inoue et al. (1995)... 

Temperature has a large effect on the mass transfer between the micelle and the stationary phase and can therefore be used to improve the efficiency of the separation. Micellar chromatography should be carried out at elevated temperature, typically around 40°C. At elevated temperatures, the effects of flow rate and surfactant concentration on the efficiency of the separation are minimized. For optimum efficiency, however, the flow rate should be minimized while still maintaining a reasonable elution time.33 Likewise, a surfactant concentration close to but above the critical micelle concentration should be used.33... 

One of the major differences between micellar chromatography and standard reversed-phase chromatography is the selectivity of the separation. As the micelle concentration is increased, solute retention decreases as a result of increased solute-micelle interactions in the mobile phase. The rate of decrease varies from solute to solute, however, since different solutes will have a different affinity for the micelles thus, inversions in retention orders are produced.34... 

Quinones et al. (2000) reported the successful use of neural networks to predict the half-life of a series of 30 antihistamines. The input for the network was derived from the output of CODES, a routine that generates descriptors for a structure based on atom nature, bonding, and connectivity. Attempts to correlate the half-life with the physicochemical parameters log Kow, pKa, molecular weight, molar refractivity, molar volume, parachor, and polarity were unsuccessful. In a subsequent study by Quinones-Torrelo et al. (2001), the authors correlated the half-life of 18 antihistamines with their retention in a biopartitioning micellar chromatography system with a resultant correlation coefficient (R2adj) value of 0.89. The correlation is explained in that the retention in this system is dependent on hydrophobic, electronic, and steric properties, which are also important in determining half-life. 

Quinones-Torrelo, C., Sagrado, S., Villanueva-Camanas, R.M., and Medina-Hernandez, M.J., Retention pharmacokinetic and pharmacodynamic parameter relationships of antihistamine drugs using biopartitioning micellar chromatography, J. Chromatogr. B, 761, 13-26, 2001. 

Another attempt to circumvent the failure of K v to model BCF well was made by Escuder-Gilabert et al. (2001), who used bio-partitioning micellar chromatography retention factor (k) ... 

The main disadvantages of micellar chromatography are the observed diminished chromatographic efficiency, higher column back pressure, and in preparative work, the need to separate the final resolved analyte from the surfactant (95) (a later section of this review will discuss this latter problem and its resolution in further detail). The higher column back pressure and part of the decreased efficiency stem from the fact that surfactant-containing mobile phases are more viscous compared to the usual hydro-organic mobile phases employed in conventional RP-HPLC (refer to viscosity data in Table X)... 

In many forms of secondary equilibria separations, the concentration of the equilibrant, or the mobile phase component which participates in the secondary equilibria, controls, at least partially, the strength and selectivity of the mobile phase. In micellar chromatography the concentration of micelles plays this role, which means that for all separations carried out with micellar mobile phases, the strength of the mobile phase can be changed while maintaining an unchanging bulk solvent composition. This unique aspect of micellar mobile phases does indeed allow the solution to "problems that cannot be solved by other means . 

A major drawback in the early reports of micellar chromatography was a serious loss of efficiency when compared to traditional hydroorganic mobile phases. If micellar mobile phases are ever to be widely accepted as a viable chromatographic technique, the efficiency achieved must at least approach that of conventional reversed-phase LC. 

The separation of anions by the use of a cationic micellar mobile phase results in a high degree of flexibility not available from other methods of ion chromatography. The importance of micelles in the mobile phase lies in their ability to participate in the partitioning mechanism. The three equilibria involved in micellar chromatography are schematically represented in Figure 1. The elution behaviour of the anionic solute depends on three partition coefficients K p, the partition coefficient between the bulk mobile phase and and the micelle K nn the partition coefficient between the bonded phase and the micelle and K mpi the partition coefficient between the bonded phase and the bulk mobile phase. 

Figure 1. The three equilibria involved in micellar chromatography.

Finally a better understanding of the effects of temperature, organic modifier and pressure on micelle stability is important if micellar chromatography is to develop and become an accepted method within the area of chromatography. 

Micellar chromatography is an advance in methodology. The research outlined in this area hopefully adds to this methodology. 

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