Reducing Cycle Time with Stacked Injections Case of Isocratic Eluents

2 Reducing Cycle Time with Stacked Injections (Case of Isocratic Eluents) For chromatographic separations performed using isocratic eluents (i.e., whose composition does not change over time), once the injected amount has been increased to its ophmal value, eluent consumption can then be reduced by stacking 

Some complex mixtures contain components with very different affinities with the stationary phase, and, as a consequence, the retention times will vary greatly. 

Using different eluents, different retention times can be observed. In this situation, the cycle time can be reduced by modifying the composition over time. 

1) Semi-continuous processes such as steady-state recycling also exist however, they are beyond the scope of this chapter [11-14]. 

Continuous processes are more efficient than batch processes, as the use of stationary phase is optimized and the amount of eluent needed for the purification is significantly reduced. The concentration of feed mixture inside the column can be much higher than it is in the case of a batch process. As a consequence, productivity is multiplied by a factor of two to five, less manpower is required, usage of stationary phase is optimized, and the amount of solvent used is reduced by a factor of two to ten. Two multicolumn continuous chromatography processes have been commercially implemented at commercial scale for pharmaceutical chiral separahons, these being the simulated moving bed (SMB) process and the Varicol process [15-17]. 

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