Elution Extrusion Mode
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Elution and Extrusion
In Elution Extrusion CCC (EECCC) the separation is started in the same manner as in single-mode CCC. However, when the run reaches a certain point (also called Vcm, such as K=1.0), mobile phase will be switched to the formerly stationary phase while maintaining the unchanged instrumental conditions, i.e., continue rotation in HSCCC and CPC (no changes in flow direction or path). This will ultimately extrude all column content. Analytes separated inside the column, that would otherwise require very large volumes of mobile phase to elute, are pushed out of the column in order of their partition coefficients. There are several advantages of this method:
- The peak width of compounds with higher K will be kept narrow, so that the resolution can be improved for strongly retained compounds
- The overall run time will be shortened since only one column volume of initial stationary phase (i.e. the new mobile phase) is needed to extrude the entire sample.
- Solvent usage is kept to a minimum.
- At the end of the experiment the instrument is loaded with stationary phase and ready for another injection.
The Three Stages of EECCC Separations
Overall, elution-extrusion countercurrent chromatography takes full advantage of the liquid nature of the stationary phase by combining regular chromatographic elution with stationary phase extrusion. EECCC has recently been shown to be a three-stage process consisting of classical elution (I), sweeping elution (II), and extrusion (III).
In addition to these advantages, EECCC also extends the "sweet spot" of high-resolution in CCC, and provides access to the otherwise practically unapproachable high-KD portion of the high-resolution chromatograms in CCC.
The Theory of EECCC
The complete mathematical treatment of the EEECC method and derivation of the equations that describe the EECCC chromatograms is detailed in the following 2007 publication by Berthod, Friesen, Inui, and Pauli:
Additional Original Literature on EECCC
Note
Access to full-text reprints of the publications requires personal or institutional subscription to the corresponding journals.
ReS and ReSS Plots of EECCC Chromatograms
Because of its coverage of all analytes with K values of zero to infinity, the x-axis scale of EECCC chromatograms require an adequate definition in order to enable their graphical representation. One recently established method to create CCC Chromatograms of EECCC runs are the Reciprocal Symmetry Plots (ReS and ReSS), in which K and 1/K of the analytes are plotted symmetrically around a midline of K=1 or a K defined by the operator, respetively. For further explanation of ReS and ReSS plots see the CCC Chromatograms section.
An Example of EECCC ReSS Plots
The following demonstrates the congruence of EECCC chromatograms with different switch points (Vcm):
