The plunger of the present disclosure includes: a plunger main body section that is made of sapphire, has a pillar shape, and includes a non-penetrating fitting hole extending in a central axis direction from one end portion; a core portion that is inserted into the fitting hole and has a higher thermal conductivity than sapphire; and a joint layer that is interposed between an inner peripheral surface and a bottom surface of the fitting hole of the plunger main body section, and an outer peripheral surface and a tip surface of the core portion, the joint layer being configured to bond the plunger main body section and the core portion. A pump includes the plunger. A liquid analysis device includes the pump.

The invention relates to devices for transferring or dispensing liquids. Hydraulic positive-displacement device for pumping and/or dispensing fluids, comprising of a working chamber in which the working body is placed, is characterized by the working body made of a composite of at least two parts the first of whichthe outside is made of sapphire, and its outer surface is congruent to the interior surface of the working chamber, the second item is placed in the inner cavity of the first part and configured to transmit the translational motion of the working body. The invention reduces the surface roughness of the working body, simplifying the process of replacing individual parts of the unit and extends the range of geometrical sizes of devices that can be manufactured.