A sample preparation system provides an automated process that dispenses appropriate amounts of solid material into wells of a microtiter plate for mixing into a suspension. The system utilizes an array of hollow tubes that are lowered into a particle reservoir such that particle material is forced up into the tubes. During loading, solid plungers in the tubes are positioned a known distance from the open end of the tubes. When the particle material is to be dispensed, the plungers are lowered to push the particle material out of the tubes and into receiving wells of the microtiter plate. The plunger stroke and internal diameter of the tubes defines the dispensed volume of particle material.