Abstract: The present invention provides a wafer centering device for a measurement apparatus, the device comprising: a body unit; a guide unit which is installed in the body unit, has a support part for supporting a wafer, and has a through-hole and; and a displacement unit which is formed to be moved in the through-hole and has a pusher for moving the wafer on the support part.

Abstract: An apparatus for liquid chromatography which detects ingredients by an electrolytic device, wherein the apparatus can detect many kinds of substances in high sensitivity by making possible to apply a wider range of electrolyzing voltage than former apparatus. The electrolytic device provided in the apparatus for liquid chromatography has a working electrode which is formed an electrically conductive diamond film on at least one side surface of an electrically conductive plate, a spacer plate of electrical insulating material which is 0.05 to 0.5 mm in thickness and has a hole, and a counter electrode which is facing to the diamond-formed surface of the working electrode while being put the spacer between the electrodes. Furthermore, an eluate inlet hole, an eluate outlet hole and a reference electrode are opened to a cavity formed by the hole of the spacer plate, and the eluate in the electrolytic device is pressurized to 1.0 to 15.0 kg/cm2.