Diluting liquid samples

Abstract

The diluter disclosed herein consists of a control and drive unit and a diluent module which is connectable to the control and drive unit to form a diluter apparatus. In the diluent module, which can be removed and replaced for the rapid and non-contaminating substitution of diluents, a diluent piston engages the walls of a cylindrical diluent reservoir which has an outlet at one end. A bore through the diluent piston receives and supports a second, smaller piston which can be moved independently of the diluent piston. With appropriate connections to the drive unit, the small piston may be moved in a direction away from the diluent outlet, thereby aspirating a small sample of liquid placed in contact with a spout which communicates with the diluent outlet. Subsequent movement of the diluent piston toward the outlet enables the dispensing from the spout of the relatively small sample of liquid along with a relatively large quantity of diluent. The drive unit includes separate, preferably coaxial, drive rods having engagement portions for releasable connection to the pistons of the diluent module. A stepping motor drives the diluent piston and a motor control unit includes selector means permitting the selection of the precise number of incremental rotations of the stepping motor's rotor, thereby enabling selection of the precise quantity of diluent to be dispensed when the diluent piston is driven toward the outlet.