A detection system comprises a housing having a sample inlet and a gas outlet, and a preconcentrator. The preconcentrator can include a microelectromechanical system (MEMS) configured to accumulate or release a dopant at selected times, and can be located inside or outside the housing. The detection system can include an ion mobility spectrometer, a mass spectrometer, or a combination thereof. A method of analyzing a substance comprises supplying a sample gas or vapor comprising the substance, accumulating a dopant in a first preconcentrator, releasing the dopant at selected times from the preconcentrator to an area containing the sample, ionizing the substance to generate detectable species, separating the detectable species, and determining the detectable species by a detection unit. The system and method allow the rapid introduction and removal of dopant to facilitate fast and accurate identification of the sample.