Real-time monitoring of trace-level VOCs by an ultrasensitive lamp-based VUV photoionization mass spectrometer

摘要

In this study, we report on the development of a lamp-based vacuumultraviolet photoionization mass spectrometer (VUV-PIMS) in our laboratory;it is composed of a radio-frequency-powered VUV lamp, a VUV photoionizer, anion-migration lens assembly, and a reflection time-of-flight massspectrometer. By utilizing the novel photoionizer consisting of aphotoionization cavity and a VUV light baffle, the baselines of the massspectra decreased from 263.6 ± 15.7 counts to 4.1 ± 1.8 counts.A detection limit (2σ) of 3 pptv was achieved for benzene after anacquisition time of 10 s. To examine its potential for real-time monitoringapplications of samples, the developed VUV-PIMS was employed for thecontinuous measurement of urban air for 6 days in Beijing, China. Strongsignals of trace-level volatile organic compounds, such as benzene and itsalkylated derivatives, were observed in the mass spectra. These initialexperimental results reveal that the instrument can be used for the onlinemonitoring of trace-level species in the atmosphere.