Micellar liquid chromatography solvent

The development of micellar liquid chromatography and accumulation of numerous experimental data have given rise to the theory of chromatographic retention and optimization methods of mobile phase composition. This task has had some problems because the presence of micelles in mobile phase and its modification by organic solvent provides a great variety of solutes interactions. 

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 ... 

Kord AS and Khaledi MG (1992) Controlling solvent strength and selectivity in micellar liquid chromatography Role of organic modifiers and micelles. Analytical Chemistry 64 1894-1900. 

Recently, Suyani and co-workers [77] have investigated the use of micellar liquid chromatography (MLC), as an alternative to to the methods given above, with ICP-MS detection. The organic solvents commonly used in HPLC mobile phases can decrease sensitivity due to excessive... 

Caruso and co-workers [7] separated alkyltin compounds using micellar liquid chromatography and tested the compatibility of this separation technique with inductively coupled plasma mass spectrometric detection (ICP-MS). This study was undertaken because many of the HPLC separations developed for these compounds involve the use of hydro-organic mobile phases, and use of organic solvents with ICP-MS results in a decrease in sensitivity due to excessive solvent loading of the plasma. Separations for many of these species were shown using 5-/im Ci8 Spherisorb silica-bonded columns, 50 mm x 4.6 mm i.d., and mobile phases containing sodium dodecyl sulfate, acetic acid, propanol, and potassium fluoride. 

High-performance liquid chromatography (HPLC) with a micellar mobile phase or with a selective pre-column or reaction detection system has also been used to determine alkylenebis(dithiocarbamaes). ° Zineb and mancozeb residues in feed were determined by ion-pair HPLC with ultraviolet (UV) detection at 272 nm. These compounds were converted to water-soluble sodium salts with ethylenediaminetetra-acetic acid (EDTA) and sodium hydroxide. The extracts were ion-pair methylated with tetrabuthylammonium hydrogensulfate (ion-pair reagent) in a chloroform-hexane solvent mixture at pH 6.5-8.S. The use of an electrochemical detector has also been reported. ... 

Micelles and cyclodextrins are the most common reagents used for this technique. Micellar electrokinetic capillary chromatography (MECC or MEKC) is generally used for the separation of small molecules [6], Sodium dodecyl sulfate at concentrations from 20 to 150 mM in conjunction with 20 mM borate buffer (pH 9.3) or phosphate buffer (pH 7.0) represent the most common operating conditions. The mechanism of separation is related to reversed-phase liquid chromatography, at least for neutral solutes. Organic solvents such as 5-20% methanol or acetonitrile are useful to modify selectivity when there is too much retention in the system. Alternative surfactants such as bile salts (sodium cholate), cationic surfactants (cetyltrimethy-lammonium bromide), nonionic surfactants (poly-oxyethylene-23-lauryl ether), and alkyl glucosides can be used as well. 

The literature of QSRR with LSS is dominated by a specific SSD, the I ER solute parameters V, E, S, A, and B, as defined in Equation 15.2. An extraordinary amount of attention has been paid to predict retention (24,25) and to establish phase selectivity in MEKC using LSER (5, 7, 26-31). Attempts to classify and to contrast micellar phases with basis on the LSER coefficients have been pursued by many researchers (5,26,27,29). Interesting approaches comprise the classification of micellar phases by the combined use of LSER parameters and retention indexes (32), the clustering of micellar systems by principal component analysis (26), the use of LSER parameters to compose vectors for characterization of lipophilicity scales (33), and, more recently, the establishment of micellar selectivity triangles (34,35) in analogy to the solvent selectivity triangle introduced by Snyder to classify solvents and ultimately mobile phases in liquid chromatography. 

Armstrong [58] has recently pioneered the use of micellar solutions as the mobile phase in liquid chromatography. This technique appears to be very powerful and, as applied to high-pressure liquid chromatography, allows the use of cheap aqueous solvents instead of expensive, and often hazardous, organic solvents. 

Typical water miscible organic solvents (e.g. methanol, acetonitrile, etc.) affect selectivity in micellar electrokinetic chromatography in a manner similar to reversed-phase liquid chromatography. The range of composition variation, however, is restricted by instability of the micelles at moderate concentrations of organic solvents, and... 

Reversed-Phase Liquid Chromatography (RPLC) is an important tool in protein chemistry. Examination of sorption isotherms revealed that alcohohc buffers did not desorb proteins near physiological pH in RPLC systems, while buffers containing a poly(ethoxy alcohol) surfactant did not desorb protein at pH 2, but they did at pH 7 with concentrations of surfactant apparently well above the critical micellar concentration (cmc) [2]. It has been proposed that a necessary condition for the desorption of a protein from a surface is that the surface tension of the solvent falls between that of the protein and the surface [6]. This condition is fiilfilled for many proteins with surfactant solutions near conditions of physiological pH and ionic strength. Therefore, it was expected that separations of proteins could be thieved in these conditions. 

See also Capillary Electrochromatography. Liquid Chromatography Micellar. Solvents. 

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