A liquid chromatography system includes a separation column, a trap column, and a first switching valve. The first switching valve is adapted to assume a first switching position for bringing a sample into the trap column in a first flow direction. The switching valve is also adapted to assume a second switching position for fluidly connecting the trap column with the separation column and providing a flow from the trap column to the separation column in a second flow direction. The second flow direction is opposite to the first flow direction. The first switching valve is adapted to assume a third switching position for fluidly connecting the trap column, with the separation column and providing a flow from the trap column to the separation column in the first flow direction.