Soczewinski model

From the general framework of the Snyder and Soczewinski model of the linear adsorption TLC, two very simple relationships were derived, which proved extremely useful for rapid prediction of solute retention in the thin-layer chromatographic systems employing binary mobile phases. One of them (known as the Soczewinski equation) proved successful in the case of the adsorption and the normal phase TLC modes. Another (known as the Snyder equation) proved similarly successful in the case of the reversed-phase TLC mode. 

Consequences of the Snyder and Soczewinski model are manifold, and their praetieal importance is very signifieant. The most speetaeular conclusions of this model are (1) a possibility to quantify adsorbents ehromatographic activity and (2) a possibility to dehne and quantify chromatographic polarity of solvents (known as the solvents elution strength). These two conclusions could only be drawn on the assumption as to the displacement mechanism of solute retention. An obvious necessity was to quantify the effect of displacement, which resulted in the following relationship for the thermodynamic equilibrium constant of adsorption, K,, in the case of an active chromatographic adsorbent and of the monocomponent eluent ... 

From the Snyder-Soczewinski model (12, 13), the entire adsorbent surface is covered by an adsorbate monolayer that consists of mobile phase. Retention is assumed to occur as a displacement process in which an adsorbing solute molecule X displaces some number n of previously adsorbed mobile-phase molecules S... 

A single solvent only rarely provides suitable separation selectivity and retention in normal-phase systems, which should be adjusted by selecting an appropriate composition of a two- or a multi-component mobile phase. The dependence of retention on the composition of the mobile phase can be described using theoretical models of adsorption. With some simplification, both the Snyder and the Soczewinski models lead to identical equation describing the retention (retention factor. A) as a function of the concentration of the stronger (more polar) solvent, (p. in binary mobile phases comprised of two solvents of different polarities [,121 ... 

To illustrate the general elution problem and its solution, let us consider the following situation. Consider a 20-component mixture with capacity factors k of the components forming a geometrical progression and exponentially dependent on the modifier concentration (molar or volume fraction c), in accordance with the Snyder-Soczewinski model of adsorption [2]. The log k versus log c plots of the 20 solutes are given in Fig. 1, which has a parallel Rf axis subordinated to the right-hand-side log k axis. It can be seen that no isocratic eluent can separate all the components. A pure modifier [c = 1.0 (100%)] separates well solutes 1-7, and the less polar solutes are accumulated near the solvent front for c = 0.1 (10%), solutes 8-14 are... 

Simplified Relationships Derived from the Snyder and Soczewinski Model... 

SIMPLIFIED RELATIONSHIPS DERIVED FROM THE SNYDER AND SOCZEWINSKI MODEL... 

As can be easily deduced, quantification of sorbent activity cannot be done in the absolute, but in relative values only. The most complete approach to this problem was derived from the Snyder-Soczewinski model of adsorption chromatography, and it will be briefly discussed here. 

Quantification of solvent elution strength is based on the Snyder-Soczewinski model of adsorption chromatography. A possibility of appropriate quantification is offered by Eq. 47. For the sorbent activity coefficient a = 1, Eq. 47 can be rewritten in the following form ... 

Abscisic acid (ABA), 784-785 Absorption measurement, 208 Acid dyes, 1015,1016 Adsorbent gradient, ISO Adsorbents, 17 Adsorption chromatography aluminas and, 17,107 Kowalska model of, 63-64 O ik model of, 61-62 Scott-Kucera model of, 62-63 silica gels and, 17,104 Synder-Soczewinski model of, 60 Alcoholic products, dyes from, 1005 Alkaloids from plants, 1040 pyrrolizidine, 1036-1040 Aluminas, 17,106-107 adsorption chromatography and, 107 partition chromatography and, 107 physical and chemical properties, 106-107 for separation of carbohydrates, 494 Amikacin, 458-461... 

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