Modes of Operation
- Reverse phase - Aqueous phase mobile - The denser phase is pumped through as the mobile phase.
- Normal phase - Organic phase mobile - The less dense phase is used as the mobile phase.
- Dual-Mode: The mobile and stationary phases are reversed part way through the run.
- Gradient Mode: The concentration of one or more components in the mobile phase is varied throughout the run to achieve optimal resolution across a wider range of polarities. For example, a methanol-water gradient may be employed using pure heptane as the stationary phase. This is not possible with all binary systems, due to excessive loss of stationary phase.
- Elution Extrusion Mode (EECCC): The mobile phase is extruded after a certain point by switching the phase being pumped into the system. For example, during the Elution portion of a separation using an EtOAc-water system running head to tail, the aqueous mobile phase is being pumped into the system, . In order to switch to extrusion mode, organic phase is pumped into the system. This can be accomplished either with a valve on the inlet of single pump, or ideally with an integrated system of two or three pumps, each dedicated either to a single phase of a binary mixture, or to an intermediate wash solvent. This also allows for good resolution of compounds with high mobile-phase affinities. It requires only one column volume of solvent and leaves the column full of fresh stationary phase.
- pH Zone Refining: Acidic and basic solvents are used to elute analytes based on their pKa.
Read more about this topic: Countercurrent Chromatography
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