Preparative chromatography modes

In the last part of this book, we apply the different models discussed earlier, particularly the ideal model and the equilibrium-dispersive model, to the investigation of the properties of simulated moving bed chromatography (Chapter 17) and we discuss the optimization of the batch processes used in preparative chromatography (Chapter 18). Of central importance is the optimization of the column operating and design parameters for maximum production rate, minimum solvent use, or minimum production cost. Also critical is the comparison between the performance of the different modes of chromatography. 

TLC can be scaled-up and used for the isolation of large (10-100 mg) quantities of pure component. The practice of the technique is similar to that for analytical, qualitative scale work. The main difference lies in the plates used. Almost all preparative scale work is carried out, in the adsorption mode, principally on silica gel plates of varying thickness, 1-5 mm, and of 20 x 20 cm dimensions. The sample is applied as a streak, either by a pasteur pipette, syringe or a motorised streak applicator . Advantage can be taken of multiple development techniques, which allow efficient separation of components of markedly different polarities. Bands incompletely resolved can be applied to a fresh plate and rechromatographed with a suitable solvent and development procedure. Once development is complete the bands of component can be scraped off with a razor blade or spatula and the component washed off the adsorbent with a suitable solvent. Plates for preparative chromatography are available with added fluorescent indicator which facilitates non-destructive location of the components. The fluorescent indicator is irreversibly bound to the silica. 

Figure 3 Fermentation modes for recombinant bacteria, yeast, and animal cells. On the left-hand side, the feed streams and harvesting streams are schematically shown for the batch, fed-batch, and continuous cultivation of microorganisms. On the right-hand side, the product concentration and the cell density are shown. For batch and fed-batch a discontinuous product concentration profile is obtained. With constitutive expression of a product, the product concentration is dependent on the cell density. Product is present in the culture supernatant during the whole production cycle and thus more susceptible to degradation. When the product formation is induction controlled, the production concentration raises sharply after addition of the inductor. The residence time of the product in the bioreactor is reduced. For continuous culture a constant product concentration profile is maintained over the entire production cycle. The residence time of the product in the bioreactor depends on the harvesting time and is shortest tor all fermentation modes when harvesting is continuously performed. Changing the mode of production can highly influence the composition of feed for preparative chromatography.

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