Chromatographic separations, basics scaling

The optimization of chromatographic separations can generally be seen as a compromise between speed, i.e., to produce the largest possible amount of data or substance per unit time, and resolution, i.e., to produce the highest possible quality of data or purity of substance. Obviously the goal for optimization differs according to the purpose of the separation and also between scale of operation. Therefore, different parameters are critical for different situations. Still, some basic rules for optimization may be applied. 

When chromatographic separations (7) are operated in a batch mode, a portion of the mixture to be separated is introduced at the column inlet. A solute-free carrier fluid is then fed continually through the column, the solutes separating into bands or zones. Some industrial operations such as mixed-vapor solvent recovery and sorption of the less volatile hydrocarbons in natural gas or natural gasoline plants are being carried out on pilot plant and semiworks scales. Continuous countercurrent systems designed along the basic principles of distillation columns have been constructed. 

This equation provides basic equation for elution chromatography. For better separation, a, N should be large. In chromatographic separation, large N can be readily achieved. A typical large-scale GC or LC column will contain of 103104 theoretical plates. 

The lifetime of a chromatographic column strongly depends on the application and on basic precautions to protect it. Some applications require to repack the column with fresh packing material after each injection (e.g., purification of specific natural substances) whereas several large-scale HPLC equipments are used continuously during few years without any significant loss of performances (e.g., chiral separations). 

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