Radiofrequency field enhanced chemical ionization with vacuum ultraviolet lamp for miniature time-of-flight mass spectrometer

It is difficult to rapidly and on-line detect trace volatile organic compounds for miniature mass spectrometry due to its limited sampling volume at slow pumping speed. In this paper, we developed a new radiofrequency field enhanced chemical ionization source (RF-ECI) with vacuum ultraviolet (VUV) lamp by coupling radiofrequency electric field and direct-current field together. The experiment results showed that the sensitivity of benzene, toluene, hydrogen sulfide and other compounds increased by 2–3 orders of magnitude under the introduction of RF-ECI comparing to traditional single photon ionization (SPI). At the same time, the reagent ion of O₂⁺ realized the charge transfer reaction chemical ionization, and the RF-ECI effectively expanded the detection range of the VUV lamp based SPI. The VUV lamp has inherent advantages in the on-site analytical instrument for its small size and low power consumption, and the VUV lamp based RF-ECI miniature time-of-flight mass spectrometer (TOFMS) has a limit-of-detection for H₂S as low as 0.0571 mg/m³, and it is expected to be used widely in the field of on-site rapid analysis.