Abstract: An apparatus for detecting chemicals in a fluid includes a preconcentrator tube connected to a bi-directional pump and to a detector. The preconcentrator tube contains a sorbent material in thermal contact with a heating element. The bi-directional pump pumps fluid in a first direction through the sorbent material, thereby causing some of the chemicals to accumulate on one side of the sorbent material. The bi-directional pump is reversed so as to pump fluid in a second opposite direction, thereby causing the accumulated chemicals to be carried to the detector. The sorbent material is heated while the bi-directional pump is reversed. Preferably, the detector is equipped with a separate pump that draws fluid to the detector.