Increased Flexibility in Multicolumn Chromatography (MC[sbnd]HPLC) via On-line Effluent Mixing Technique

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Abstract
In continuation of our work dealing with multicolumn HPLC (MC[sbnd]HPLC) we describe in this paper an on-line on-column fraction trapping technique based on effluent mixing. To a normal two-column switching set-up (in this case with two RP columns) an additional high-pressure pump gets inserted into the connection line between column A and column B via a low dead volume mixing tee. The in-line respectively off-line switching of pump B and the mobile phase B is time controlled by using a high pressure switching valve. With this set-up it is possible to mix on-line an effluent fraction from column A and transferred onto column B with a highly polar and pH-controlled (e.g. aqueous buffer) new effluent, to reduce or adjust significantly the overall elution strength of this mixed transferred solvent. Thus, several chromatographically effective possibilities can be created in a simple manner, which are for example: (a) pronounced peak compression respectively on-column concentration on column B; (b) due to low elution strength and/or pH adjustment during the trapping period on column B, increments to the overall selectivity of the column switching set-up can be added creating multidimensionality via mobile phase switching; (c) combining the heart cut with the effluent mixing technique enables analysis of trace peaks eluted on the back flank of an overloaded main peak.