Active Solvent Modulation (ASM) is a solution for improving solvent compatibility between the first and the second dimension.
The 1D solvent in the sample loop may impair separation if it has a high elution strength with respect to the second dimension column. This may result in unretained elution, broad and distorted peaks, often with a loss of separation. ASM modulates the content of the sampling loop by temporary dilution with weak solvent before it reaches the 2D column. In this way, the analytes in the sample are focused on the column head. After the enrichment of the analytes, the valve switches to its final through-loop position. This workflow is enabled by the 2D-LC Valve ASM G4243A.