Abstract: A sample duct in a carrier line is isolated by three-way valves blocking the flow of carrier or flushing liquid from reservoirs. The sample duct may be connected to a loading syringe and to a sample reservoir respectively by the valves. When the sample duct is connected into the carrier line, pressurized carrier fluid may convey the sample for analysis through a manifold comprising valves through which reagents may be introduced from reservoirs. The sample then passes through a thermostatically controlled reaction tube to a valve which switches it between waste and an outlet leading to a detector for analysis. The carrier and flushing fluids and the reagents are pressurized by gas from an inlet which is conveyed via an overpressure vent to the reservoir by lines. Rigid inert tubing is used throughout the carrier line, sample duct, manifold and reaction tube.