Articles | Volume 8, issue 11
Research article
04 Nov 2015
Research article |  | 04 Nov 2015

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

W. Q. Sun, J. N. Shu, P. Zhang, Z. Li, N. N. Li, M. Liang, and B. Yang

Abstract. In this study, we report on the development of a lamp-based vacuum ultraviolet photoionization mass spectrometer (VUV-PIMS) in our laboratory; it is composed of a radio-frequency-powered VUV lamp, a VUV photoionizer, an ion-migration lens assembly, and a reflection time-of-flight mass spectrometer. By utilizing the novel photoionizer consisting of a photoionization cavity and a VUV light baffle, the baselines of the mass spectra 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 an acquisition time of 10 s. To examine its potential for real-time monitoring applications of samples, the developed VUV-PIMS was employed for the continuous measurement of urban air for 6 days in Beijing, China. Strong signals of trace-level volatile organic compounds, such as benzene and its alkylated derivatives, were observed in the mass spectra. These initial experimental results reveal that the instrument can be used for the online monitoring of trace-level species in the atmosphere.

Short summary
A novel ultrasensitive VUV photoionization mass spectrometer is developed to monitor trace-level VOCs in real time. By employing a light baffle in the photoionizer, the background noise is efficiently suppressed and the detection limit reaches to a low pptv level. Continuous monitoring of VOCs in urban air demonstrates the strength of this instrument. This study reveals that the new technique may have the capability of ranking with the PTR-MS for field measurements.