PURPOSE:To prevent the mixture of impurities upon trap removal by connecting remaining ports of on/off valves with connected inlets and outlets of an on/off valved hermetic trap having at least four ports to the outlet channel and the discharge channel of a fractionation column via switch valves. CONSTITUTION:When fractionation and purification of aimed components are finished, a four-way cock 5 (channel switch valve) is switched over to discharge unnecessary components out of the system via a three-way cock 7, and a four- way cock 14 (on/off valve) is closed to remove a trap 12 together with cock 14. When a detector 3 detects that components to be fractionated and purified have eluted again, the three-way cock 7 is switched over, and a four-way cock 6 (channel switch valve) is switched over at a predetermined timing to connect the outlet and the discharge channel of a fractionation column 2 to the inlet and the outlet of a U-tube 17 via a four-way cock 15 (on/off valve), thereby collecting aimed components in a trap 13. Removing the traps 12, 13 together with the on/off valves 14, 15 enables the mixture of impurities to be prevented.
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