A liquid chromatography system includes a pumping system with a selector valve in fluidic communication with a pump inlet. The selector valve switches between a first position, in which the selector valve fluidically couples a solvent reservoir to the pump inlet, and a second position, in which the selector valve fluidically couples a pressurized source of liquefied carbon dioxide (for example) to the pump inlet. The liquid chromatography system can perform as a HPLC system (or as an UPLC system) when the selector valve is in the first position and as a CO2-based chromatography system when the selector valve is in the second position. The selector valve can have a third position in which both the fluidic pathway between the solvent reservoir and the pump inlet and the fluidic pathway between the pressurized source and the pump inlet are blocked. This shut-off position advantageously facilitates system maintenance.