Chromatographic elution axial

The derivation of analytical expressions for the moments of a band in chromatography is tedious. It involves successive differentiations of the Laplace transform solution of the chromatography model used. Several more expedient methods have been proposed to simplify these derivations for axial chromatography [43,44]. A simple and generalized method was described by Lee et al. [45] for the moments in chromatographic elution peaks with any geometric configuration (axial or radial) and any kinetic models. 

Calibration of Gel Permeation Chromatograph Polystyrene Calibration. A plot of molecular size in (S) versus elution volume for polysty-rene standards in dichloromethane showed deviation from linearity at about 2,200 which may be attributed to Imperfect column resolution, peak broadening, axial dispersion and skewing. The extensive tailing of the chromatograms of high molecular weight polystyrene standards observed in dichloromethane has also been reported in the literature (23-26). 

It is well known that all elution curves, obtained by diverse chromatographic techniques, show the following common feature They cannot be reduced to a vertical straight line1 even if a strictly monodisperse sample is injected into the column, but always show a bell-shaped curve with a finite width, evidently not originating in the MWD of the injected sample. This experimental result can be explained by an axial acceleration of the injected species by the stream of the column liquid, leading... 

Obviously, the aim is for a chromatographic separation in which peak width is narrow relative to the time of elution (wi/Vr is minimized), i.e., the number of theoretical plates is maximized. There are three main factors that give rise to band broadening (1) multiple path effect (eddy diffusion), (2) axial (longitudinal) diffusion, and (3) mass transfer—slow transfer/equilibration between mobile and stationary zones. 

When there is a size distribution in the particles packed in a chromatographic column, the distribution does not change the first moment of the elution peak while it may affect peak broadening through the contribution not only of intraparticle diffusion but also of other transport processes such as axial dispersion. The evaluation of the latter effect is not clear but it is possible to make a prediction of the effect of particle size distribution on the intraparticle diffusion contribution, 8i. This was done by Chihara, Suzuki and Kawazoe (1977) for several typical distribution functions. The effeevt of the particle size distribution can be accounted for by introducing a correction factor, F, into the expression of 6d. 

The concept of the continuous annular chromatography (CAC) was introduced by Martin in 1949. The packed bed of the adsorbent occupies the annular space between two coaxial cylinders. The bed rotates past a fixed port through which sample is continuously fed. The eluent percolates downward through the bed. Substances elute as helical bands due to the simultaneous axial chromatographic process and bed rotation as shown in Fig. 13. The stronger the adsorption of a given substance is, the further away... 

The Micromeritics Instrument Corporation is currently developing an integrated hydrodynamic chromatograph. Problems with development and/or manufacture have resulted in some delays, but a prototype should be available for purchase late in 1982. The instrument will apparently contain its own microprocessor for control of instrument operation, and also for deconvolution of the data to account for axial dispersion. Elution times are not available at this time, but if they can be kept to a minimum, and if sampling, dilution and injection functions can be automated, this instrument may provide highly accurate, on-line particle size distribution data for reactor control. 

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