Two-pump at-column-dilution configuration for preparative liquid chromatography-mass spectrometry.

Preparative liquid chromatography-mass spectrometry (LC-MS) is widely used in parallel synthesis schemes to expedite purification. Recently, an alternative sample loading scheme, at column dilution, has been shown to dramatically increase the mass loading capacity of LC-MS purification methods. The prototype system utilized separate sample loading and binary gradient pumps. We report here a configuration for effecting at-column dilution using only the two pumps that provide the binary gradient flow. The advantages of a two-pump configuration are reduced cost, reduced space requirements, simplified control, and reduced service and maintenance issues. The two-pump at-column-dilution configuration is demonstrated for large- and small-scale LC-MS purifications. Purification on scales appropriate for high-throughput parallel synthesis can be achieved with small-scale chromatography using at-column dilution; purification of 20 mg of material is demonstrated using a 4.6 mm x 150 mm column and a flow rate of 3 mL/m. Reducing the scale of chromatography required for LC-MS purification has significant benefits, including the following. It requires less expensive columns, consumes less solvent, generates smaller-volume fractions (shorter dry-down time and the ability to collect into small-volume collector formats, such as 96-well plates), and has the potential for faster separations.