Preparative chromatography sample mass overload

Preparative Chiral Chromatography The Loading Capacity of a Column The Maximum Sample Volume Sample Volume Overload Sample Mass Overload Preparative Chromatography Apparatus Solvent Reservoirs Pumps... 

Preparative chromatography involves the collection of individual solutes as they are eluted from the column for further use, but does not necessarily entail the separation of large samples. Special columns can be designed and fabricated for preparative use, but for small samples the analytical column can often be overloaded for preparative purposes. Columns can be either volume overloaded or mass overloaded. Volume overload causes the peak to broaden, but the retention time of the front of the peak... 

Since the goal of preparative chromatography is the production of large quantities of purified compounds, a large sample volume or a large mass of sample or a combination of both is usually applied to the column. This leads to additional effects not commonly encounter in analytical chromatography, such as shifts in retention times and additional broadening of the peaks. In the discussions in the remainder of the book, we tacitly implied the ab ce of such overload effects. For example, we assumed that the concentration of the analytes remains within the linear portion of the adsorption isotherm, while... 

Even with overloaded conditions the ratio between sample mass and the amount of stationary phase required is low and uneconomical, as in most cases it will not be higher than 10 mg g. A totally different approach for preparative liquid chromatography is displacement chromatography (Fig. 20.5). In this method, comparatively enormous sample loads are brought on to the chromatographic bed. As the different compounds of the sample mixture show different affinities towards the stationary phase, they displace each other from the adsoptive (in a... 

While analyses made in gradient elution often involve the use of small and dilute samples, the column is often overloaded in preparative gradient elution chromatography. This causes the adsorption isotherms to be nonlinear and competitive. Therefore, interference effects become important. Furthermore, the mass transfer resistances can be very significant, especially for macromolecules. Various dispersive effects, such as axial dispersion and the mass transfer resistances often coimter-balance the thermodynamic effects of adsorption and desorption... 

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