The sample gas is enriched by PDMS membrane and then ionized by vacuum ultraviolet lamp (10.6 ev) to produce molecular ions. The ions are introduced into the ion trap by special ion gate design technology, then trapped in the ion trap by digital square wave. The ion is scanned linearly by resonance excitation technology, and the first-order mass spectrum of complete molecular ion information is obtained to realize the quantitative and qualitative analysis of samples. At the same time, based on the high-efficiency cascade function of DT-100, the molecular ions in the ion trap can be dissociated to produce fragment ions, and more detailed sample mechanism information can be obtained, which can realize the further accurate characterization of samples.