Chromatography thermodynamics

Davis, J.M., Pompe, M., Samuel, C. (2000). Justification of statistical overlap theory in programmed temperature gas chromatography thermodynamic origin of random distribution of retention times. Anal. Chem. 72, 5700-5713. 

VaUaya, A., Eundamentals of reversed phase chromatography thermodynamic and exothermodynamic treatment, J. Liq. Chromatogn Relat. TechnoL, 28, 965, 2005. 

Schurig, V, and Schmidt, R. (2003) Extraordinary chiral discrimination in inclusion gas chromatography. Thermodynamics of enantioselectivity between a racemic perfluorodiether and a modified 7-cyclodextrin. J. Chromatogr. 1000, 311-324. 

M. Roth, Binary mobile-phase fluids in supercritical fluid chromatography Thermodynamics of the cosolvent effect and application to the use of helium pressure carbon dioxide cylinders... 

Again it is seen that only when second order effects need to be considered does the relationship become more complicated. The dead volume is made up of many components, and they need not be identified and understood, particularly if the thermodynamic properties of a distribution system are to be examined. As a consequence, the subject of the column dead volume and its measurement in chromatography systems will need to be extensively investigated. Initially, however, the retention volume equation will be examined in more detail. 

By measuring the retention volume of a solute, the distribution coefficient can be obtained. The distribution coefficient, determined over a range of temperatures, is often used to determine the thermodynamic properties of the system this will be discussed later. From a chromatography point of view, thermodynamic studies are also employed as a diagnostic tool to examine the actual nature of the distribution. The use of thermodynamics for this purpose will be a subject of discussion in the next chapter. It follows that the accurate measurement of (VV) can be extremely... 

An interesting and practical example of the use of thermodynamic analysis is to explain and predict certain features that arise in the application of chromatography to chiral separations. The separation of enantiomers is achieved by making one or both phases chirally active so that different enantiomers will interact slightly differently with the one or both phases. In practice, it is usual to make the stationary phase comprise one specific isomer so that it offers specific selectivity to one enantiomer of the chiral solute pair. The basis of the selectivity is thought to be spatial, in that one enantiomer can approach the stationary phase closer than the other. If there is no chiral selectivity in the stationary phase, both enantiomers (being chemically identical) will coelute and will provide identical log(Vr ) against 1/T curve. If, however, one... 

The latter compound can be isolated from the reaction mixture by chromatography on acid-washed alumina. Similar treatment of the trans-ketone (117a) followed by isolation and chromatography on alumina gives the same equilibrium mixture. The structure of the thermodynamically more stable ketone (116a) was proved by its conversion by Wolff-Kishner reduction to the hydrocarbon (118) independently synthesized from the known... 

The basic principle of chromatography separations can be described by thermodynamics using the distribution coefficient K (12) ... 

Diastereoselective amino nitrile formation from the following ulose may, however, be attributed to thermodynamic control. Flash chromatography of the product provides only one ri bo-derivative28. 

A portion of the product was heated to reflux with methanolic sodium methoxide to convert it into the thermodynamic mixture of trans- (ca. 65%) and cis- (ca. 35%) isomers. Small amounts of the isomers were collected by preparative gas chromatography using an 8 mm. by 1.7 m. column containing 15% Carbowax 20M on Chromosorb W, and each isomer exhibited the expected spectral and analytical properties. The same thermodynamic mixture of isomers was prepared independently by lithium-ammonia reduction5 of 2-allyl-3-methyl-cyclohex-2-enone [2-Cyclohexen-l-one, 3-methyl-2-(2-propcnyl)-],6 followed by equilibration with methanolic sodium methoxide. 

There are very few examples of asymmetric synthesis using optically pure ions as chiral-inducing agents for the control of the configuration at the metal center. Chiral anions for such an apphcation have recently been reviewed by Lacour [19]. For example, the chiral enantiomerically pure Trisphat anion was successfully used for the stereoselective synthesis of tris-diimine-Fe(ll) complex, made configurationally stable because of the presence of a tetradentate bis(l,10-phenanthroline) ligand (Fig. 9) [29]. Excellent diastereoselectivity (>20 1) was demonstrated as a consequence of the preferred homochiral association of the anion and the iron(ll) complex and evidence for a thermodynamic control of the selectivity was obtained. The two diastereoisomers can be efficiently separated by ion-pair chromatography on silica gel plates with excellent yields. 

Patapoff, T. W., Mrsny, R. J., and Lee, W. A., The application of size exclusion chromatography and computer simulation to study the thermodynamic and kinetic parameters for short-lived dissociable protein aggregates, Anal. Bio-chem., 212, 71, 1993. 

DA Hoagland. Unified thermodynamic model for polymer separations produced by size exclusion chromatography, hydrodynamic chromatography, and gel electrophoresis. ACS Symp Ser 635 173-188, 1996. 

Substituted adducts similar to 50 have been obtained from the reactions carried out in chlorobenzene and in toluene 19>. Whereas methanesulphonyl azide does not thermolyze appreciably below 120 °C, when a solution of CH3SO2N3 in benzene was heated at 80 °C for 100 hr, 47 (ca. 0.5%) could be detected by thin layer chromatography but no 49 38>. Almost all the azide remained undecomposed. Similarly, very small, amounts of 47 were observed, together with much tar and undecomposed azide, on photolysis of CH3SO2N3 in benzene at room temperature or at 80 °C 10). This confirms that azepine formation is the kinetically controlled process, while the anilides are the products of thermodynamic control. 

Davis, J.M. (2004). Assessment by Monte Carlo simulation of thermodynamic correlation of retention times in dual-column temperature programmed comprehensive two-dimensional gas chromatography. J. Sep. Sci. 27, 417. 

On the other hand, optically active telluroxides have not been isolated until recently, although it has been surmised that they are key intermediates in asymmetric synthesis.3,4 In 1997, optically active telluroxides 3, stabilized by bulky substituents toward racemization, were isolated for the first time by liquid chromatography on optically active columns.13,14 The stereochemistry was determined by comparing their chiroptical properties with those of chiral selenoxides with known absolute configurations. The stability of the chiral telluroxides toward racemization was found to be lower than that of the corresponding selenoxides, and the racemization mechanism that involved formation of the achiral hydrate by reaction of water was also clarified. Telluroxides 4 and 5, which were thermodynamically stabilized by nitrogen-tellurium interactions, were also optically resolved and their absolute configurations and stability were studied (Scheme 2).12,14... 

Sugiyama, T., Takeuchi, T., Suzuki, Y. (1975) Thermodynamic properties of solute molecules at infinite dilution determined by gas-liquid chromatography. I. Intermolecular energies of w-alkane solutes in C28 - C36 w-alkane solvents. J. Chromatogr. 105,265-272. 

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