A method of performing a chromatographic separation includes modulating a portion of a flowstream to a trap column to retain at least one analyte from the flowstream on the trap column. A flow of a modifier is provided through the trap column to generate an elution comprising the at least one analyte. A flow of a compressible fluid-based chromatography (CFC) mobile phase or CFC solvent is merged with the elution from the trap column to generate a diluted elution. Carbon dioxide may be used as the CFC solvent or as a component of the CFC mobile phase. The diluted elution is provided to a CFC column where at least one analyte is focused at a head of the CFC column. Examples of a flowstream that may be used include an eluent from a chromatography column or a fluid flow from an extraction system.