Column switching chromatography — What is the defining operational feature of a column-switching method?

Introduction / Context:
Column switching uses valve-based plumbing to direct portions of the eluate from a first column onto a second column. This enables online sample cleanup, heart-cutting of target bands, or multidimensional separations without physically changing columns during a run.

Given Data / Assumptions:

• Valves (2-, 6-, or 10-port) route flow paths.
• First-dimension column performs initial separation or trapping.
• Second-dimension column provides additional resolution or orthogonal selectivity.

Concept / Approach:
Distinguish true column switching from manual hardware swaps or simple flow pulsing. The hallmark is controlled transfer of selected fractions between columns under valve control, often called heart-cutting or comprehensive 2D separations.

Step-by-Step Solution:

Verification / Alternative check:
Chromatograms from 2D-LC or GC×GC show improved separation of coeluting species compared with one dimension.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing column switching with gradient changes; they are orthogonal method controls.

Final Answer:
Compounds trapped on one column are selectively eluted to a second column.