Quasi-trapping chemical ionization source based on a commercial VUV lamp for time-of-flight mass spectrometry.

The application of VUV lamp-based single photon ionization (SPI) was limited due to low photon energy and poor photon flux density. In this work, we designed a quasi-trapping chemical ionization (QT-CI) source with a commercial VUV 10.6 eV krypton lamp for time-of-flight mass spectrometry. The three electrode configuration ion source with RF voltage on the second electrode constitutes a quasi-trapping region, which has two features: accelerating the photoelectrons originated from the photoelectric effect with VUV light to trigger the chemical ionization through ion-molecule reaction and increasing the collisions between reactant ion O2(+) and analyte molecules to enhance the efficiency of chemical ionization. Compared to single SPI based on VUV krypton lamp, the QT-CI ion source not only apparently improved the sensitivity (e.g., 12-118 fold enhancement were achieved for 13 molecules, including aromatic hydrocarbon, chlorinated hydrocarbon, hydrogen sulfide, etc.) but also extended the range of ionizable molecules with ionization potential (IP) higher than 10.6 eV, such as propane, dichloroethane, and trichloromethane.