Stationary phases in liquid chromatography

Today, lipophilicity can be determined in many systems that are classified by the characteristics of the nonaqueous phase. When the second phase is an organic solvent (e.g. n-octanol), the system is isotropic, when the second phase is a suspension (e.g. liposomes), it is anisotropic, and when the second phase is a stationary phase in liquid chromatography, it is an anisotropic chromatographic system [6]. Here, we discuss the main aspects of isotropic and anisotropic lipophilicity and their biological relevance the chromatographic approaches are investigated in the following chapter by Martel et al. 

The last several years have seen an enormous growth in the number and use of chiral stationary phases in liquid chromatography [742,780-791]. Some problems with the gas chromatographic approach are that the analyte must be volatile to be analyzed and larger-scale preparative separations are frequently difficult. For entropic reasons relatively high temperatures tend to minimize the stability differences between the diastereomeric complexes and racemization of the stationary phase over time may also occur. The upper temperature limit for phases such as Chirasil-Val is about 230 C and is established by the rate of racemization of the chiral centers and not by column bleed. Liquid chromatography should be s ior in the above... 

Surface-confined ionic liquids as stationary phases in liquid chromatography... 

Any chromatographic process is associated with the distribution of the analyzed substance between the mobile and the stationary phase. In liquid chromatography the solvent, with the volume V0 in the interparticle space, moving along the column at a certain speed, is the mobile phase, and a porous adsorbent, with an overall pore volume of V, is the stationary phase. The distribution coefficient, Kd, equal to the ratio between the concentration of the substance in the stationary and the mobile phase, determines the retention volume, VR, of a given substance in the column according to the basic chromatographic equation... 

E. Turiel and A. Martin-Esteban, Molecularly Imprinted Polymers Toward Highly Selective Stationary Phases in Liquid Chromatography and Capillary Electrophoresis, Anal. Bioanal. Chem. 2004,378, 1876 K. Haupt, Molecularly Imprinted Polymers The Next Generation, Anal. Chem. 2003, 75, 376A. 

Turiel E, Martin-Esteban A (2004) Molecularly imprinted polymers towards highly selective stationary phases in liquid chromatography and capillary electrophoresis. Anal Bioanal Chem 378(8) 1876—1886... 

H. Irth, R. Tocklu, K. Welten, G. J. de Jong, R. W. Frei and U. A. Th Brinkman, Trace enrichment on a metal-loaded thiol stationary phase in liquid chromatography effect of analyte structure and pH value on the (de)sorption behaviour , J. Pharm. Biomed. Anal. 7 1679-1690(1989). 

Fujimura, K., Ueda, T., and Ando, T., Retention behavior of some aromatic compounds on chemically bonded cyclodextrin silica stationary phase in liquid chromatography, Anal. Chem., 55, 446, 1983. 

Another example of such complexes is the interactions between the chiral 18-crown-6 and phenyl glycine, which is presented in Figure 22-26 [68]. Later, the chiral 18-crown-6 was immobilized on silica gel and polystyrene resins and used as a stationary phase in liquid chromatography for the separation of amino ester salts. Despite the fact that baseline separation was obtained... 

J.H. Knox Theory of HPLC, Part II Solute Interactions with the Mobile Phase and Stationary Phases in Liquid Chromatography . In C.F. Simpson (ed.), Practical High Performance Liquid Chromatography. Heyden and Son, Chichester 1976. 

Sorption Effect A nonlinear effect due to the difference in the partial molar volumes of the component in solution in the mobile phase, and adsorbed on the stationary phase. In liquid chromatography this effect is negligible. It is important in gas chromatography. 

JT Eleveld, HA Claessens, JL Ammerdorfer, AM van Herk, CA Cramers. Evaluation of mixed-mode stationary phases in liquid chromatography for the separation of charged and unchaiged oligomer-like model compounds. J Chromatogr A 677 211-227, 1994. 

The binding to a MIP and the corresponding CP is usually evaluated either by batch incubations with polymer and analyte or by packing the polymer into a column and applying it as the stationary phase in liquid chromatography. The final use of the MIP often determines the preferred method. In batch-wise binding... 

Isotherms can also be obtained by frontal chromatography [171-173]. The MIP is then packed into a column and used as the stationary phase in liquid chromatography. A solution of known concentration of analyte is applied continuously to the column until a breakthrough curve is obtained. After washing the column, the procedure is repeated with increasing concentrations of analyte. The amount analyte bound for each concentration is calculated from the breakthrough curves. 

Parameters of interest to determine for MIPs used as stationary phases in liquid chromatography are the retention factors [k = (t - t0)/to, where t is the retention of the analyte and t0 is the void], the separation factors (a = k1/k2, where k, and k2 are the retention factors of compound 1 and 2) and the resolution (R) [175, 176], For MIPs used as stationary phases in solid-phase extraction, the recovery is also of interest. 

Chromatography - A method for separation of the components of a sample in which the components are distributed between two phases, one of which is stationary while the other moves. In gas chromatography the gas moves over a liquid or solid stationary phase. In liquid chromatography the liquid mixture moves through another liquid, a solid, or a gel. The mechanism of separation of components may be adsorption, differential solubility, ion-exchange, permeation, or other mechanisms. [6]... 

The mobile phase is the vaporized sample in gas chromatography or the solvent used to elute the sample over the stationary phase in liquid chromatography. 

From the beginning, a wide range of different materials have been used as stationary phases in liquid chromatography. Their selection depends primarily on three key properties chemical stability, mechanical stabihty, and specific surface area. The chemical stability is important for achieving the greatest possible compatibility with the mobile phase used, and on this depends also the possibihty of bringing the analytes to be determined into solution. 

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