A liquid chromatograph has switching valves as a flow passage switching mechanism and an automatic sampler as an injection section. The valve includes an inlet, a hollow cylindrical main body sealingly connected at one end thereof to the inlet, a pilot chamber having a sleeve slidably mounted within the main body and an operating pressure adjustment connected to another end of the main body adjacent another end of the pilot chamber for varying the threshold operating pressure of the valve. % of a polyolefin that has been modified with at least one functional group selected from a carboxyl, an acid anhydride, an epoxy groups or mixtures containing at least one of the foregoing functional groups, each based on the total combined weight of the resin composition, exclusive of any filler. A multi-channel readout system is coupled to the plurality of position sensitive detector planes. The present invention further discloses a process for preparing the hydrogenation catalyst, and a use of said hydrogenation catalyst in the purification of crude terephthalic acid.