Chromatographic separation 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... 

In theory, SEC of proteins depends only on their molecular size. Sometimes the size of a protein varies with the ionic strength of the buffer (5,6). The concentration of salt not only affects the conformation of the protein, but can also influence the chromatographic separation itself. Additional retention... 

D. L. Massart, C. Janssens, L. Kaufman and R. Smits, Application of the theory of graphs to the optimalisation of chromatographic separation schemes for multicomponent samples. Anal. Chem., 44 (1972) 2390-2399. 

HETP = height equivalent to a theoretical plate. It is derived from the plate theory of distillation which is a confusing concept having no basis in fact in the context of modem chromatographic separations. Nevertheless the terms plate number and plate height are still very widely used. 

Bartle, K.D. (1993). Introduction to the theory of chromatographic separations. In Gas Chromatography A Practical Approach, ed. Baugh, P.J., Oxford University Press, Oxford, pp. 1-14. 

There are, in fact, three theories that have gained virtually wide recognition and acceptance in describing a gas chromatographic separation, namely ... 

M. Medic-Saric, G. Stanic and I. Bosnjak, The use of information theory and numerical taxonomy methods for evaluating the quality of thin-layer chromatographic separations of flavonoid constituents of matricariae flos. Pharmazie 56 (2001) 156-159. 

The theoretical treatment of the hydrophobic effect is limited to pure aqueous systems. To describe chromatographic separations in RPC Horvath and Melander developed the solvophobic theory [47]. In this theory, no special assumptions are made about the properties of solute and solvent, and besides hydrophobic interaction electrostatic and other specific interactions are included. The theory has been valuable to describe the retention of nonpolar [48], polar [49], and ionizable [50] solutes in RPC. The modulation of selectivity via secondary equilibria (variation of pH, ion pair formation [51]) can also be described. On the other hand, it is not a problem to find examples of dispersive interactions in literature, e.g., separation of carotinoids with a long chain (C30) RP gives a higher selectivity compared to standard RP C18 cyclohexanols are preferentially retarded on cyclohexyl-bonded phases compared to phases with linear-bonded alkyl groups. 

In a chromatographic separation procedure the parameters of the chromatographic system (stationary phase, flow, temperature, etc.) have to be selected respectively optimized with respect to some criterion (resolution, time, etc.). In gas chromatography retention data series are published and used for the sttidy of solvent/solute interaction, prediction of the retention behaviour, activity coefficients, and other relevant information usable for optimization and classification. Several clKmometrk techniques of data anal s have been employed, e.g. PCA, numerical taxonomic methods, information theory, and j ttern recognition. 

In recent years HPLC technique has been perfected. A large number of food components may be separated with HPLC. Many excellent books have been published on HPLC theory and thousands of articles have been written on chromatographic separations of food-related components. 

This chapter introduces the basic theory and terminology governing chromatographic separations and the equations used to calculate the effectiveness of the analytical system. With this information, the best separation mechanism and column characteristics for a given problem can be chosen,... 

The possible development of LA into a cross-over chemical between carbohydrates and petrochemicals has recently spurred the development of more efficient procedures for its production. Most start from cheap starting materials such as lignocellulose residues and waste paper in acidic medium at approx. 200 °C the theoretical yield of such a procedure is 0.71 kg kg-1 (see Fig. 8.36). In a patent application for a two-stage procedure the claimed yields were 62-87% of the theory, depending on the raw material [195]. A much simpler, extrusion-based procedure has been described but even when fitted with a second stage the yield was not better than 66% of the theory [196]. Efficient DSP is not trivial and the chromatographic separation that has been described [197] is obviously not compatible with the aimed-for commodity status of LA. Alternatively, the LA can be esterified in situ [197]. 

The majority of chromatographic separations as well as the theory assume that each component elutes out of the column as a narrow band or a Gaussian peak. Using the position of the maximum of the peak as a measure of retention time, the peak shape conforms closely to the equation C = Cjjjg, exp[-(t -1] ) The modelling of this process, by traditional descriptive models, has been extensively reported in the literature. 

W. H. Pirkle and T. C. Pochapsky, Theory and design of chiral stationary phases for direct chromatographic separation of enantiomers, in K. K. Unger (ed.). Packings and Stationary Phases in Chromatographic Techniques, Marcel Dekker, New York, 1990, p. 783. 

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