An automated GC sampling system is described which permits real-time verification of vapor stream concentrations used in the testing and development of chemical sensors. The system consists of a computer-actuated injector loop placed in-line between a VG-400 vapor generator (Microsensor Systems) and a surface acoustic wave (SAW) sensor. Optimization of the system was performed by comparing the predicted VG-400 vapor output with the GC-determined vapor stream concentrations. The system was utilized in the identification of hystersis effects in a polymer-coated SAW sensor.