(EN) A liquid sample is prepared at a preparation site and then processed, e.g. in an HPLC column. Fluid supplies (20A, 20B) supply working fluids at flow rates measured by flow meters (24A, 24B). Rotary valve (12) has six external ports (12A-12F). The outputs of the working fluids are combined and delivered to port (12A). Port (12B) is connected via loading conduit (181) to ~LC column (18), the output of which flows to detector (26). A controller (22) controls the operation of valve (12) and supplies (20A, 20B), using input from the flow meters.