Adsorption chromatograph

The surface of activated alumina is a complex mixture of aluminum, oxygen, and hydroxyl ions which combine in specific ways to produce both acid and base sites. These sites are the cause of surface activity and so are important in adsorption, chromatographic, and catalytic appHcations. Models have been developed to help explain the evolution of these sites on activation (19). Other ions present on the surface can alter the surface chemistry and this approach is commonly used to manipulate properties for various appHcations. 

Samples and reference substances should be dissolved in the same solvents to ensure that comparable substance distribution occurs in all the starting zones. In order to keep the size of the starting zones down to a minimum (diameter TLC 2 to 4 mm, HPTLC 0.5 to 1 mm) the application volumes are normally limited to a maximum of 5 xl for TLC and 500 nl for HPTLC when the samples are applied as spots. Particularly in the case of adsorption-chromatographic systems layers with concentrating zones offer another possibility of producing small starting zones. Here the applied zones are compressed to narrow bands at the solvent front before the mobile phase reaches the active chromatographic layer. 

The great leap forward for chromatography was the seminal work of Martin and Synge (7) who in 1941 replaced countercurrent liquid-liquid extraction by partition chromatography for the analysis of amino acids from wool. Martin also realized that the mobile phase could be a gas rather than a liquid, and with James first developed (8) gas chromatography (GC) in 1951, following the gas-phase adsorption-chromatographic separations of Phillips (9). 

Thin-layer chromatography usually involves the adsorption chromatographic separation of substance mixtures into polarity groups. It is well known that clean looking chromatographic peaks can hide several substances. For instance, primary, secondary and tertiary alcohols are to be found at very nearly the same hRf. 

The specific retention of sample molecules to be separated in a straight phase or adsorption chromatographic system is mainly determined by two factors their interactions with polar surface centers of the solid stationary phase, and by the different sample solubility in the rather nonpolar mobile phase. The most important interactions... 

Adsorption, a surface phenomenon, is the basis of many gas or liquid mixture separation and purification methods. It is also the basis of adsorption chromatographic methods used for the analysis of complex mixtures. The knowledge of adsorption mechaiusms is useful in choosing the suitable systems providing optimum separation. 

Snyder and Soczewinski created and published, at the same time, another model called the S-S model describing the adsorption chromatographic process [19,61]. This model takes into account the role of the mobile phase in the chromatographic separation of the mixture. It assumes that in the chromatographic system the whole surface of the adsorbent is covered by a monolayer of adsorbed molecules of the mobile phase and of the solute and that the molecules of the mobile phase components occupy sites of identical size. It is supposed that under chromatographic process conditions the solute concentrations are very low, and the adsorption layer consists mainly of molecules of the mobile phase solvents. According to the S-S model, intermolecular interactions are reduced in the mobile phase but only for the... 

Jewell, D.M. Weber, J.H. Bunger, J.W. Plancher, H. Latham, D.R. Ion-Exchange, Coordination and Adsorption Chromatographic Separation of Heavy-End Petroleum Distillates, Anal. Chem. 1972, 44, 1391. 

Physicochemical properties of L zeolites and of clinoptilolite were studied by adsorption, chromatographic, spectral, and ther-mogravimetric methods. The sodium form of L zeolite is characterized by better adsorption with respect to water and benzene vapor and by higher retention volumes of C C hydrocarbons and CO than potassium and cesium forms. The activation energy of dehydration determined by the thermogravimetric method decreases on going from the sodium to cesium form of L zeolite. When calcium is replaced by potassium ions in clinoptilolite, the latter shows a decreased adsorption with respect to water vapor. The infrared spectra of the L zeolite at different levels of hydration show the existence of several types of water with different bond characters and arrangements in the lattice. 

Sulfur compounds in the gas oil fractions from two bitumens (Athabasca oil sand and Cold Lake deposit)> a heavy oil (Lloydminster) from Cretaceous reservoirs along the western Canada sedimentary basin, and a Cretaceous oil from a deep reservoir that may be mature (Medicine River) are investigated. The gas oil distillates were separated to concentrates of different hydrocarbon types on a liquid adsorption chromatographic column. The aromatic hydrocarbon types with their associated sulfur compounds were resolved by gas chromatographic simulated distillation and then by gas solid chromatography. Some sulfur compounds were further characterized by mass spectrometry. The predominant sulfur compounds in these fractions are alkyl-substituted benzo- and dibenzothiophenes with short side chains which have few dominant isomers. 

The modification of chromatographic properties, unlike in GC, is usually of secondary importance. Often, however, a lowering of the polarity of certain molecules (e.g., sugars) is observed which enables the separation on adsorption chromatographic systems with more convenient solvent systems. This in turn may decrease retention times and consequently improve detection limits. 

Adsorption Chromatographic Fractions. Examination of the data of Table V shows a tendency for distillates of lower-rank-coal liquids to contain more saturate material and less polyaromatic-... 

Peuravuori, J. and Pihlaja, K. (1997b) Isolation and characterization of natural organic matter from lake water two different adsorption chromatographic methods. Environ. Int., 23, 453 164. 

Gas-Phase Adsorption Chromatographic Determination of Thermochemical Data and Empirical Methods for their Estimation... 

Part I Basic principles of the determination of adsorption properties using gas-phase adsorption chromatographic methods... 

Volatilization processes, combined with gas adsorption chromatographic investigations, are well established methods in nuclear chemistry. Fast reactions and high transport and separation velocities are crucial advantages of these methods. In addition, the fast sample preparation for a-spectroscopy and spontaneous fission measurements directly after the gas-phase separation is a very advantageous feature. Formation probabilities of defined chemical compounds and their volatility can be investigated on the basis of experimentally determined and of predicted thermochemical data, the latter are discussed in Part II of this chapter. 

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]. 

Due to the extremely low production rates of transactinides in the nuclear fusion reactions, the chemical characterizations are carried out on a single atom level. The chemical reaction products are characterized on the basis of their behavior in the separation process or, exactly speaking, in the gas adsorption chromatographic process. In this process the formation probability of defined chemical states of transactinides and the subsequent interaction of the formed molecules with a solid state surface are studied. 

The experimental proof of such correlations for defined classes of pure substances is essentially for the prediction of adsorption properties of transactinides and their compounds. Therefore, a variety of gas adsorption chromatographic experiments were carried out with carrier free amounts of different radioisotopes using selected modified surfaces as stationary phases. The use of carrier free amounts is necessary to experimentally obtain adsorption conditions at nearly zero surface coverage. 

The net adsorption enthalpies and the predicted sublimation enthalpies (see Method 1) were used to calculate the adsorption enthalpies of transactinides on selected metal surfaces (Method 11). The metals, which are presented in Table 4, can be used as stationary phase in gas adsorption chromatographic experiments for selective gas chemical separations or, in the case of high adsorption interaction, as strong fixation materials for the sample preparation in the measurement of transactinides. 

Snyder studied the adsorption energy of 7-azaindole by means of linear elution adsorption chromatograph. It showed an adsorption energy nearly identical to that of 2-aminopyridine and a-carboline, and appeared characteristic of the — N=C— NH group. 

Within one type of zeolite, adsorption, chromatographic, catalytic, and other properties are determined to a certain extent by the nature of ion exchange cations, by their number per unit cell, by the degree of population of single centers (positions) in the crystal framework, and by other things. 

Eichler B, Eichler R (2003) Gas-phase adsorption chromatographic determination of thermochemical data and empirical methods for their estimation. In Schadel M (ed) The chemistry of superheavy elements. Kluwer, Dordrecht, p 205... 

It is to be noted that the considerations presented above demonstrate the application of the gas chromatographic version of the molecular probes method, proposed by authors in [46]. This method can be used to obtain reliable estimates of the size and shape of micropores on a chromatographic adsorbent surface. The fact that these estimates agree with the results of adsorption chromatographic measurements at non-zero coverage (Figure 2) supports the conclusion regarding the applicability of the method to the study of surface-porous adsorbents. 

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