A piston carrier (46) supports an elongated, slender piston rod (12) for reciprocation in a pump cylinder (30) to pump fluid into and out of the cylinder (30). The piston rod (12) is made of a material such as sapphire or zircon and has a diameter less than about ten millimeters, and the pump (10) can provide flows of from about 50 to about 250 microliters per minute at pressures of several hundred bars. A drive motor (18) rotates a threaded screw (58) and a drive nut (70) of a drive system (26) applies a linear drive force to the piston carrier(46). A ball and socket connection (74) between the drive system (26) and the piston carrier (46) avoids the need for precise alignment to prevent breakage of the fragile piston (12). A magnet (80) in the socket (78) holds the ball (76) in place and avoids the need for a spring or other mechanical holder. The socket (78) also includes a ring (88) of a low reluctance material surrounding the ball (76) to increase the magnetic retention force. |