Abstract: The construction and performance study is reported for a newly developed proton transfer reaction time of flight mass spectrometer (PTR-TOFMS). The threshold voltage of the discriminator on data acquisition board is optimized. The results show that when the threshold voltage is 0.33V, the intensity ratio of H316O+ (m/z 19) and H318O+ (m/z 21) is about 500:1. The relationship between the distribution of water clusters ion H3O+ (H2O) n=0,1,2,3 and the reduced electric field in drift tube was studied. The results show that when E/N is 139 Td, the water cluster ions are well suppressed, and the purity of the ion H3O+ is more than 99%. The resolutions at different m/z were also investigated. The results show that the best resolution is at m/z 124 with RMAX=2653. The performance of the PTR-TOFMS instrument was tested by using different concentrations of ethanol gas. The results showed that the linear dynamic range of the PTR-TOFMS instrument can reach three orders of magnitude, and the detection limit can reach 3.8ppb. PTR-TOFMS was used to detect the laboratory air to get a mass spectrum of different volatile organic compounds (VOCs). The newly developed PTR-TOFMS can be used for on-line monitoring trace volatile organic compounds, and it will be of great value in the fields of environment, food, medicine and other fields.

Key words: proton transfer reaction time of flight mass spectrometer, threshold voltage, resolution, volatile organic compounds