Boxcar injections

The technique of boxcar injections (not to be confused with boxcar chromatography) can be extremely productive for iso-cratic elution in any mode of chromatography and should always be considered when scaling up a separation. The preparative HPLC of an enantiomeric mixture utilising a chiral stationary phase is described here to demonstrate the approach for separation of a binary mixture. 

In order to increase productivity it was decided to use boxcar injections to isolate the required component. This process, described diagrammatically in Figure 5.10, utilizes repeat... 

It is important to note that the technique of boxcar injections is by no means restricted to chiral separations and should always be considered for any separation performed under isocratic elution. 

In displacement chromatography, a pulse of mixture is injected, and this is followed by a step of a single component called a displacer, which is adsorbed more strongly than any of the mixture components. After a certain period of time, during which the profiles of each pulse become reorganized, an isotachic pulse train is formed. In the isotachic train, each component forms its own concentration boxcar, with a height that depends on the component and displacer isotherms as well as on the displacer concentration, and a width proportional to the amount of the corresponding component in the sample [14], [15]. 

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