Reaction chromatography desorption

Both GC and LC may be operated in one of several modes. The principal modes currently used for large-scale separations are elution, selective adsorption or desorption, and simulated countercurrent chromatography. In addition, reaction and separation can be combined in a single column with unique advantages. Elution is the most used and best developed form of the technique and is described first. 

Wall, D. B., Finch, J. W., and Cohen, S. A. (2004). Comparison of desorption/ionization on silicon (DIOS) time-of-flight and liquid chromatography/tandem mass spectrometry for assaying enzyme-inhibition reactions. Rapid Commun. Mass Spectrom. 18 1482-1486. 

Sparks et al. (1980b) introduced a continuous flow method (next subsection) that is quite similar in principle to liquid-phase column chromatography. This method was used to study potassium adsorption dynamics on soils and clay minerals (Sparks and Jardine, 1981 Sparks and Rechcigl, 1982 Jardine and Sparks, 1984 Ogwada and Sparks, 1986a,b,c), silicate sorption on soils (Miller et al., 1986), S04 sorption and desorption on soils (Hodges and Johnson, 1987), and Al reactions on clay minerals and peat (Jardine etal., 1985a). 

The analytically important features of Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometry (1) have recently been reviewed (2-9) ultrahigh mass resolution (>1,000,000 at m/z. < 200) with accurate mass measurement even 1n gas chromatography/mass spectrometry experiments sensitive detection of low-volatility samples due to 1,000-fold lower source pressure than in other mass spectrometers versatile Ion sources (electron impact (El), self-chemical ionization (self-Cl), laser desorption (LD), secondary ionization (e.g., Cs+-bombardment), fast atom bombardment (FAB), and plasma desorption (e.g., 252cf fission) trapped-ion capability for study of ion-molecule reaction connectivities, kinetics, equilibria, and energetics and mass spectrometry/mass spectrometry (MS/MS) with a single mass analyzer and dual collision chamber. 

The area is an important surface parameter for catalytic studies. It is needed to evaluate the rate constant of the surface reaction from the kinetics as well as to allow a fair comparison to be made of the effectiveness of different catalysts. Areas are commonly determined by nitrogen or krypton gas adsorption interpreted by the Brunauer-Emmett Teller (BET) isotherm [30, 32], A number of other methods has been proposed and utilised including microscopy, isotopic exchange, chromatography, gas permeability, adsorption from solution, and negative adsorption (desorption) of co-ions [30, 33]. 

The strength of interaction of hydrocarbons with metallic surfaces serves as a probe to investigate the role of desorption and adsorption of these species in a variety of catalytic reactions (Table XXIX). Ostrovskii and Medvedkova (242) used calorimetry and gas chromatography to measure heats of adsorption of C4-C8 hydrocarbons over Co before and after use in Fischer-Tropsch synthesis. For the fresh samples, the adsorption of aliphatic hydrocarbons was reversible, and the initial heat of adsorption increased with increasing chain length of the adsorbate. It appeared that the saturated hydrocarbons were adsorbed with the C—C bond axis parallel to the surface, and the contributions from the CH3 and CH groups were calculated as cHj = -4.63 and mol". With these values, the experimental... 

Reversed-flow gas chromatography methodologies have been utilized for the investigation of various catalytic processes, and a large number of physicochemical quantities related to the kinetics of the elementary steps (adsorption, desorption, surface reaction) and the nature of the active sites have been determined. These parameters are summarized as follows ... 

Kimura, K., et al. Direct determination of a polymeric hindered amine light stabilizer in polyproplylene by thermal desorption-gas chromatography assisted by in-line chemical reaction, Analyst, 2000, 125, 465. 

The dissociative adsorption - associative desorption type of reaction also takes place when Ln or An trichlorides are chemically volatilized into the carrier gas containing a rather large concentration of A12C16 vapors. Chromatography evidently proceeds due to the equilibria like ... 

The kinetics of adsorption-desorption is rarely slow in preparative chromatography, and most examples of a slow kinetics are foimd in bioaffinity chromatography, or in the separation of proteins. Thus, there are few cases in which a reaction-kinetic model is appropriate. This model is important, however, because there are many cases where it is convenient to model the finite rate of the mass transfer... 

The VERSE method was extended to describe the consequences of protein de-naturation on breakthrough curves in frontal analysis and on elution band profiles in nonlinear isocratic and gradient elution chromatography [45]. Its authors assumed that a unimolecular and irreversible reaction taking place in the adsorbed phase accormts properly for the denaturation and that the rate of adsorption/desorption is relatively small compared with the rates of the mass transfer kinetics and of the reaction. Thus, the assumption of local equilibrium is no longer valid. Consequently, the solid phase concentration must then be related to the adsorption and the desorption rates, via a kinetic equation. A second-order kinetics very similar to the one in Eq. 15.42 is used. 

Apparent dispersion coefficient, Dapi The apparent dispersion coefficient lumps all the contributions to axial dispersion arising from axial molecular diffusion, tortuosity, eddy diffusion, and from a finite rate of mass transfer, adsorption-desorption, or other phenomena, such as reactions, in which the eluites may be involved. It is used in the equilibrium-dispersive model of chromatography to ac-coimt for the finite efficiency of the column (Eq. 2.53 and 10.11). See equilibrium-dispersive model. 

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