Adsorption chromatographic examination

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-... 

The critical micellar concentrations of anionic/nonionic surfactant mixtures examined are low in a saline medium, so that, at the concentrations injected in practice, the chromatographic effects resulting from the respective adsorption of monomers are masked. Such surfactants propagate simultaneously in the medium in the form of mixed micelles. 

Headspace analysis involves examination of the vapours derived from a sample by warming in a pressurized partially filled and sealed container. After equilibration under controlled conditions, the proportions of volatile sample components in the vapours of the headspace are representative of those in the bulk sample. The system, which is usually automated to ensure satisfactory reproducibility, consists of a thermostatically heated compartment in which batches of samples can be equilibrated, and a means of introducing small volumes of the headspace vapours under positive pressure into the carrier-gas stream for injection into the chromatograph (Figure 4.25). The technique is particularly useful for samples that are mixtures of volatile and non-volatile components such as residual monomers in polymers, flavours and perfumes, and solvents or alcohol in blood samples. Sensitivity can be improved by combining headspace analysis with thermal desorption whereby the sample vapours are first passed through an adsorption tube to pre-concentrate them prior to analysis. 

The next problem to be examined deals with the effect of water contained in the adsorbent on the chromatographic behaviour of macromolecules. The role of water in adsorption chromatography on polar adsorbents such as silica gel is extremely important63,64), because its varying content in the adsorbent often yields poorly reproducible results. 

The most common adsorption systems consist of silica gel or alumina adsorbents in association with an organic solvent system. The adsorbent can exert a considerable influence on the separation of compounds. Alumina and silica gel, for example, have significantly different properties and can result in quite different separations. Activation of the adsorbent also influences sample retention. The presence of water on the adsorbent decreases the adsorbent activity due to blockage of active sites. If large quantities of water are present, a partition system may be set up which may extensively change the retention times due to the different chromatographic principle involved. Table 2.1 compares results obtained for the separation of the insecticide carbaryl (Sevin) and its hydrolysis product 1-naphthol on alumina and silica gel. Comparisons between activation and deactivation are made. The results show that separation of the two components is reversed with the two adsorbents examined. In most cases, activation of the plates caused the/ f values to increase relative... 

HPLC is ideally suited to examine adsorption kinetics in the working conditions of column immunoassays. In this technique, high flow rates and minimized column volumes are required to perform rapid on-line immunodetections. The column capacities and residence times in the column are parameters that influence the efficiency of the immunoreactor. Kinetic studies using the chromatographic format will be useful to understand the process better and optimize the methodology. 

Chromatographic measurements were made for the adsorption of benzene, toluene and m-xylene on molecular sieving caibon (MSC) in supercritical fluid CO2 mixed with organics. Supercritical chromatograph packed with MSC was used to detect pulse responses of organics. Adsorption equilibria and adsorption dynamics for organics were obtained by moment analysis of the response peaks. Dependences of adsorption equilibrium constants, K., and micropote difiiisivity, D, on amount adsorbed were examined. 

SRC, a detailed examination of the composition of these coal liquids is of fundamental importance. Numerous procedures have been published previously for investigating the composition of liquids derived from coal. In general, these procedures combine separation techniques with a variety of spectroscopic methods to provide the desired quantity of structural information. The separation techniques used include methods based on solubility fractionation (4,5), methods combining solubility fractionation and adsorption chromatography (6), and liquid chromatographic procedures for chemical fractionation (7,8). Chemical reactions also have been used to separate coal liquid asphaltenes into acidic and basic fractions (9). 

Application of bis-(2-ethylhexyl) orthophosphate as a liquid ion exchanger in the complete or selective extraction of alkaloids from a buffered aqueous phase has been described. The behaviour of the salts of various alkaloids upon titration with base has been compared.Correlations have been made between the Rf of a number of alkaloids and the pH of an aqueous buffer solution which extracts half of the alkaloid from an aqueous solution. The stabilization of alkaloid solutions has been discussed. " Chromatographic separations of alkaloids by ion-exchange, adsorption, thin-layer, paper, and liquid chromatography have been reviewed. Reference lists have been compiled for methods and applications published in 1970—73 of chromatography and of electrophoresis of alkaloids on paper and thin layers. The optimum composition of Dragendorff s reagent for efficient alkaloid precipitation has been examined. ... 

Adsorption (desorption) energies or enthalpies of molecules and atoms on various surfaces are of primary and major interest in the experimental gas-phase radiochemical studies of the heaviest elements. In practice, pertinent data can be obtained almost exclusively in the experiments based on chromatographic principles. In the pioneering works [1-3] the required values were derived using the simplest description of the processes in columns in terms of molecular kinetics (see Sect. 4.2). Later [4] the task of finding the adsorption enthalpies was examined using a thermodynamic approach. It revealed that the molecular-kinetic treatment... 

Inverse gas chromatographic measurements may be carried out both at infinite dilution and at finite solute concentrations [1]. In the first case vapours of testing solutes are injected onto the colurtm and their concentrations in the adsorbed layer proceed to zero. Testing substances interact with strong active sites on the examined surface. The retention data are then converted into, e.g. dispersive component of the surface free energy and specific component of free energy of adsorption. In the second case, i.e. at finite solute concentrations, the appropriate adsorption isotherms are used to describe the surface properties of polymer or filler. The differential isosteric heat of adsorption is also calculated under the assumption that the isotherms were obtained at small temperature intervals. 

Adsorption of proteins onto surfaces involves a complex interplay of reversibility, exchange, conformational change, irreversible attachment, and denaturation. Several of these processes may be followed by measurement of the circular dichroism of adsorbed species and of desorbed material. The profile of chromatographically adsorbed material also contains, in principle, the details of the complex kinetics. Some aspects of each of these processes are examined. 

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