The sample gas is introduced into the reaction chamber through polydimethylsiloxane (PDMS) membrane, ionized by vacuum ultraviolet (10.6 ev) to produce molecular ions with their own characteristics. Molecular ions fly in the vacuum TOF mass analyzer on the same path. The ion with small mass-to-charge ratio (m/z) reaches the end first, and the ion with large m/z reaches the end later. Thus, the qualitative and quantitative analysis of different substances is carried out according to the realization of the flight time at the terminal point.