Abstract: A pneumatic/hydraulic sample handling system which includes a source of alternative vacuum and pressure, a normally closed, selectively operable valve to permit flow through the system withdrawing a known aliquot from a source of sample, directing said aliquot to a vessel for analysis, an isolation chamber disposed in the flow path between said source of vacuum and pressure and said vessel and having inlets respectively coupled into the flow path and a relief valve arranged between the isolation chamber and said source of vacuum and pressure, said isolation chamber having an outlet, a conduit coupling said outlet to a waste depositary, pressure differential sensitive check valve interposed in said conduit between said outlet and said waste depositary, and a microcomputer circuit arranged to control the operation of said system in accordance with a predetermined procedure.