An on-line system that performs concentration and solvent exchange in order to improve a detection level of analytes by a liquid chromatograph (LC) is provided. The on-line system comprises: a first pump and a second pump for supplying a solvent; a liquid chromatograph (LC) including a separation column (SC) connected to the first pump; a trapping column (TC) for collecting the analytes separated from the separation column; a concentration column (CC) for concentrating the analytes collected in the trapping column (TC); a detector; and first to third switching valves that communicate fluid with at least one of the first or second pumps. An analysis method using the same is also provided.