Synchronized Discharge Ionization for Analysis of Volatile Organic Compounds Using a Hand-Held Ion Trap Mass Spectrometer

The sensitivity of mass analysis is highly dependent on the efficiencies of the sample introduction, analyte ionization, and subsequent ion transfer to the mass analyzer. For miniature mass spectrometry (MS) systems, it is highly desirable to maximize the amount of the samples that can be introduced at the pumping capability highly compromised and to have the MS analysis performed with simple electronics and robust in-vacuum components. In this study, a discharge ionization source synchronized with the sample introduction has been developed for hand-held mass spectrometers with discontinuous atmospheric pressure interfaces (DAPI). The flow rate of the sample introduced with a DAPI can be much higher than that allowed with a conventional continuous atmospheric pressure interface. The pressure variation associated with the DAPI operation was used to turn on and off the synchronized discharge ionization (SDI). For analysis of volatile organic compounds (VOCs) in air samples, the SDI has been shown to be soft and molecular ions of the VOCs have been observed as the major species. Since the ions could be transferred directly to the ion trap mass analyzer without a barrier for maintaining pressure differences, high sensitivity in chemical analysis was also achieved, with limits of detection (LODs) better than 1 ppbv obtained for PAHs (polycyclic aromatic hydrocarbons) in air.