Elution chromatography theory

In a chromatographic separation, the individual components of a mixture are moved apart in the column due to their different affinities for the stationary phase and, as their dispersion is contained by appropriate system design, the individual solutes can be eluted discretely and resolution is achieved. Chromatography theory has been developed over the last half century, but the two critical theories, the Plate Theory and the Rate Theory, were both well established by 1960. There have been many contributors to chromatography theory over the intervening years but, with the... 

Recalling that a separation is achieved by moving the solute bands apart in the column and, at the same time, constraining their dispersion so that they are eluted discretely, it follows that the resolution of a pair of solutes is not successfully accomplished by merely selective retention. In addition, the column must be carefully designed to minimize solute band dispersion. Selective retention will be determined by the interactive nature of the two phases, but band dispersion is determined by the physical properties of the column and the manner in which it is constructed. It is, therefore, necessary to identify those properties that influence peak width and how they are related to other properties of the chromatographic system. This aspect of chromatography theory will be discussed in detail in Part 2 of this book. At this time, the theoretical development will be limited to obtaining a measure of the peak width, so that eventually the width can then be related both theoretically and experimentally to the pertinent column parameters. 

Early theories of elution chromatography developed by Wilson, Glueckauf, De Vault " and others, established the found-... 

Volume 31 Gradient Elution in Column Liquid Chromatography. Theory and Practice by P. Jandera and J. Churacek... 

PJandera and J.Churafcek, Gradient Elution in Column Liquid Chromatography Theory and practice, Elsevier, Amsterdam, 1985. 

Guiochon, G., Golshan-Shirazi, S. Theory of optimizing of the experimental conditions of preparative elution chromatography optimizing the column efficiency, Anal. Chem., 1989b, 61, 1368-1382. 

The theory of simple waves applies to large-volume injections, i.e., to the profiles obtained upon injection of rectangular profiles which are so wide that the injection plateau has not been entirely eroded when the band elutes. Then, simplifications of the solution occur because there is a constant state, the concentration plateau. This solution is not valid in overloaded elution chromatography when the injection volume is sufficiently small that the injection plateau has eroded and disappeared by the time the band elutes from the column. It is important to discuss this solution, however, because it takes a finite time for the profile of even a narrow rectangular injection to decay, and the band profile during that period is given by the simple wave solution. Also, this solution is the basis for a method of determination of competitive equilibrium isotherms (Chapter 4, Section 4.2.4). 

Plateau concentrations Several plateaus are considered in chromatography theory, besides the trivial plateau concentration corresponding to the elution of the top of a wide rectangular band. These are (i) the plateaus of the zones in the iso-tachic train in displacement chromatography, (ii) the plateaus of the less retained components displaced by the more retained ones in frontal analysis (concentration higher than the feed concentrations), and (ui) the rear plateau of the more retained component whose band tags along the band of a less retained component (concentration lower than the feed concentration). 

J. W. Nolan and L. R. Snyder, Gradient Elution Chromatography, in Encyclopedia of Analytical Chemistry, Vol. 13, Theory and Instrumentation, 11342 Chichester Wiley, 2000. 

The peak recorded in a chromatogram represents the distribution of molecules in a band as it elutes from the column, the overall broadness being conveniently m sured in terms of the width of the peak. A number of independent factors such as sample-injector and detector characteristics, temperature and column retention processes, contribute to the dispersion of molecules in a band and band broadening. The cumulative effect of small variations in these factors is described in statistical terms as the variance, cr, in the elution process. Classical chromatography theory considers that the separation process takes place by a succession of equilibrium steps, the more steps in a column the greater the column efficiency with less band broadening (variance) occurring, therefore... 

The activity coefficient is the most important and fundamental property in the thermodynamic study of liquid mixtures. It is a measure of the deviation of the behaviour of a component in a mixture from ideality and it has been interpreted by various theories of liquid mixtures. Gas-liquid elution chromatography offers a rapid method of determining this property at infinite dilution. Conder and Purnell have developed a method of determining activity coefiicients at finite concentrations and this has recently been used by other workers. " To do this, the elution technique must be supplemented by... 

II - The theory of gas-liquid chromatography has been applied to the behaviour of low concentration of various vapours as the solute gas, in the column-supported liquid as the solvent, to obtain the vapour activity coefficient in the solvent at infinite dilution by elution chromatography and at higher concentrations by frontal analysis (23, 33, 45). 

Explain the meaning of each term in the development of the solute movement equations and use this theory for both linear and nonlinear isotherms to predict the oudet concentration and temperature profiles for a variety of different operations including elution chromatography, adsorption with thermal regeneration, PSA, SMB, and ion exchange... 

In almost all cases, the experiments yielded values a> 1. The heavier isotope is enriched in the solution phase and is eluted first. The theory of isotope separation by elution chromatography and the procedure for the calculation of the separation factor from experimental data was elaborated by Glueckauf. For the case of displacement chromatography the theory was developed by Kakihana and Oi. 

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