Adsorption chromatographic techniques

Analysis of Blood Gases with Gas Adsorption Chromatographic Techniques J. Appl. Physiol. 16 374-377 (1961) ... 

Chromatography is based on the same principle as adsorption. Chromatographic techniques can be used to measure a wide variety of thermodynamic, kinetic, and physico-chemical properties. Separation occurs because of differing velocities of travel of components in the mobile and stationary phases. Theoretical plate model can be applied to chromatography. Chromatographic methods can be classified as gas and liquid chromatography depending on the nature of the mobile phase. 

The lack of calorimetric data is particularly evident in the case of the adsorption of gases on oxides or on oxide-supported metals, i.e., on solids similar to most industrial catalysts. Moreover, adsorption calorimeters are generally used at temperatures that are much lower than those usually found in industry, and it would be difficult indeed to adapt most usual adsorption calorimeters for the measurement of heats of adsorption of gases on industrial catalysts at elevated temperatures. The present success of gas chromatographic techniques for determining heats of reversible adsorption may be explained by the gap between the possibilities of the usual adsorption calorimeters and the requirements of industrial catalysis research. 

The process whereby a solute is transferred from a mobile to a stationary phase is called sorption. Chromatographic techniques are based on four different sorption mechanisms, namely surface adsorption, partition, ion-... 

In each chromatographic technique, one of the four mechanisms predominates, but it should be emphasized that two or more may be involved simultaneously. Partition and adsorption frequently occur together and in paper chromatography, for example, ion-exchange and exclusion certainly play minor roles also. 

Column chromatographic techniques were originally used as preparative tools but over the years major advances have taken place. HPLC is now a highly developed technique and a wide range of stationary phases are available. These enable partition, adsorption, gel permeation, affinity and ion-exchange chromatography to be performed. 

Adsorption chromatography. This chromatographic technique is best known because of its use in the last century as a preparative method of separation. Stationary phases have made a lot of progress since Tswett. who used calcium carbonate or sugar. The separation of organic compounds on a thin layer of silica gel or alumina with solvent as a mobile phase are examples of this type of chromatography. Solutes bond to the stationary phase because of physisorption or chemisorption interactions. The physico-chemical parameter involved is the coefficient of adsorption. 

In the rest of the chapter, various chromatographic methods will be discussed. You should recognize that no single chromatographic technique relies solely on adsorption or partition effects. Therefore, little emphasis will be placed on a classification of the techniques instead, theoretical and practical aspects will be discussed. 

Using a gas chromatographic technique (6-11), apparent heats of adsorption... 

Affinity chromatography is an adsorption method based on the recognition between a ligand immobilized on a solid matrix and a biomolecule to be separated. The main difference between this method and other chromatographic techniques is the high interaction specificity between molecules and stationary phase. 

The exchange of NaBr and KBr with HC1 reaches an equilibrium in which, near to room temperature, a mixed Cl /Br surface is at equilibrium with a gaseous HCl/HBr mixture whose composition depends on the surface anion ratio, but which is typically about 1 mole % HBr. This equilibrium was discovered in the laboratory of one of us (LGH) about eighteen years ago [96], but the topic proved difficult to pursue because of the difficulty of quantitative analysis of the gas mixture. Eventually, a temperamental but workable gas chromatographic technique [97] having provided the key to this analysis, we were able to show that the equilibrium is highly non-ideal [98]. The bromide surface apparently undergoes a two-dimensional phase transition, induced by HC1 or HBr adsorption, close to room temperature, in which the halide ions become mobile,... 

In this chapter, we concentrate on the role of the intermolecular interactions at interfaces based on the surface dynamics, the surface free energy at a given temperature and the surface energy (or enthalpy) of a solid. Contact angle and gas chromatographic techniques are respectively chosen for the studies of wettability and adsorption phenomena because of their simplicity and clearness. The degree of adhesion at interfaces between unlike solid substances is also discussed from a viewpoint of intermolecular interactions. 

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