Adsorbents in gas chromatography

Mishin, V. I., Dobychin, S. L. Porous PTFE as adsorbent in gas chromatography of metal- -diketone chelates. Zh. Prikl. Khim, Leningr. 43, 1584 (1970). — Anal. Abstr. 

The formalism can easily be adapted to a PC-based program for an evaluation of the AH°ads from gas adsorption chromatographic results and, vice versa, to predict the behavior of an adsorbate in gas chromatography from its known adsorption data. The formulas used in the PC-based simulation are given here. For their derivations see [17]. 

Kiselev reviewed and made fundamental studies of adsorbents in gas chromatography. He attempted to eliminate the heterogeneity of the surfaces of adsorbent solids to improve their selectivity. He classified adsorbents in terms of their specificity. Graphitized carbon black is a nonspecific adsorbent and silica and zeolite are specific adsorbents. The adsorptive properties and the tailing of peaks can be greatly modified by the addition of a small amount of liquid to a large-area solid. The maximum temperature limit is then that of the liquid. 

Alluli et al. [119] demonstrated, the effective use of synthetic inorganic adsorbents in gas chromatography. Clear separations of hydrocarbons and mercaptans on crystalline zirconium phosphate were obtained. 

The stability constants of complexes for charge transfo have allowed evaluation of ionization potentials for some dienes [123]. The densities of 3d 7t-electrons of metallic chlorides employed as adsorbents in gas chromatography were also determined by chromatography [124]. 

Cyclodextrin derivative used as a chiral adsorbent in gas chromatography. 

Chemically Modified Adsorbents (Bonded-Phase Silica as Adsorbent in Gas Chromatography)... 

In the derivation of Equation 2 it was assumed that the adsorption isotherm is linear. This is generally the case in gas chromatography as a very small quantity of pulsed gas is injected. (Normally less than 4 cm3 of pulsed gas was injected into a column packed with 400 grams of adsorbents.)... 

Used for polar compounds such as alcohols, glycols, ketones, aldehydes has also been used for polychlorinated biphenyls and phthalates more data are provided in the Adsorbents for Gas Chromatography table... 

In gas chromatography (GC), a gaseous solute (or the vapour from a volatile liquid) is carried by the gaseous mobile phase. In gas-liquid partition chromatography, the stationary phase is a non-volatile liquid coated on the inside of the column or on a fine support. In gas-solid adsorption chromatography, solid particles that adsorb the solute act as the stationary phase. 

The situation is more complex for liquid-solid equilibria. The surface tension of solids is not readily measured. In liquid-solid equilibria the adsorbate always has to compete, at least with the solvent which is in large excess, for access to the solid sirrface, a phenomenon that does not take place in gas-solid equilibria imder the conditions prevailing in gas chromatography [5]. As a consequence, most of our imderstanding of liquid-solid equilibria remains empirical. 

The definition of the hold-up time is simple in gas chromatography because the interactiorrs between mobile and stationary phases are practically negligible. This is not so in liquid chromatography [163-165]. The density of the mobile phase is not the same in the bulk and in the monolayer in contact with the surface of the adsorbent. The situation is more complex in RPLC because the bonded layer swells when the proportion of the organic modifier in the mobile phase increases [32,166,167]. The organic modifier dissolves in the bonded layer and, when its concentration in this layer is sufficient, some molecules of water may also penetrate it. The hold-up time of a column is a fxmction of the nature and concentration of the organic modifier in an aqueous solution [168,169]. In order to predict accurately the elution band profiles, it might be necessary to account for the dependence of the hold-up volume on the mobile phase composition, which requires the use of a different mass balance equation in which the phase ratio has been left in the differential elements [170]. 

Sorption Effect A nonlinear effect due to the difference in the partial molar volumes of the component in solution in the mobile phase, and adsorbed on the stationary phase. In liquid chromatography this effect is negligible. It is important in gas chromatography. 

Abraham et al. [64] characterized fullerene as adsorbent in gas-solid chromatography experiment. From the adsorption isotherms, gas-solid partition coefficients defined by Eq.(35), were calculated ... 

The methods of column packing preparation well known in gas chromatography practice [24] give the possibility to coat the silica gel surface with the monolayer of a given surface concentration or with the monolayer in SC state with a well-defined threedimensional excess if the specific surface area of adsorbent is known. On the other hand, inverse gas chromatography allows to determine the specific surface area of silica gel if aliphatic alcohol is used as a liquid stationary phase [25]. 

The most important adsorbents in gas-adsorption chromatography are macroporous silica (26, 27, 74). Silica carriers used in chromatography were described by Gavrilova, Bryzgalova, and co-workers (Moscow State University) (104-106). 

The use of transition metal chlorides as modified adsorbents in gas—liquid chromatography has been described [101]. 

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