Patent ID: 7556731

Claim:
A liquid chromatograph comprising: a mobile-phase-sending-unit having a plurality of solvent flow passages for sending solvents different from each other; a mixer unit provided downstream of the mobile-phase-sending-unit to mix solvents sent from the mobile-phase-sending-unit, the mixer unit having a first mixer and a second mixer having a capacity larger than that of the first mixer; a sample injection portion for injecting a sample; a concentration liquid sending unit for sending a liquid for transferring a sample to be concentrated; a trapping column for concentrating the sample by trapping components of the sample; an analysis column for separating the sample into individual components; a detector for detecting each of the components separated by the analysis column; and a flow passage switching mechanism having a first multi-port valve connected to the second mixer and the sample injection portion, a second multi-port valve connected to the trapping column and the analysis column, and a port-to-port connection flow passage for connecting the first and second multi-port valves, wherein the first mixer is connected to the first multi-port valve, the second multi-port valve or the port-to-port connection flow passage, the flow passage switching mechanism switching among a normal analysis flow passage formed by connecting the mobile-phase-sending-unit, the second mixer, the sample injection portion, the analysis column and the detector in this order, a concentration flow passage formed by connecting the concentration liquid sending unit, the second mixer, the sample injection portion and the trapping column in this order, and a concentration analysis flow passage formed by connecting the mobile-phase-sending-unit, the first mixer, the trapping column, the analysis column, and the detector in this order so that any one of the three flow passages is selectively formed, and the mobile-phase-sending-unit being set so that the flow rate of a mobile phase becomes smaller when the concentration analysis flow passage is selected than when the normal analysis flow passage is selected.