Development And Application Of Membrane Inlet Time-of-Flight Mass Spectrometry And Radio Frequency Discharge Ion Source

Volatile organic compounds(VOCs) in environment pollution, water pollution,unexpected fire and explosion are strong teratogenic and mutagenic. So the online detection of VOCs plays an emphasis on human health and environment. The traditional instruments have large volume and long analysis time, time-of-flight mass spectrometer(TOF-MS) has been widely used for environment monitoring and industrial process monitoring due to its simplicity, high resolution and sensitivity, broad applicability and microsecond scanning speed.A portable orthogonal acceleration reflection TOF-MS system combined with a vacuum ultraviolet(VUV) lamp single photon ionization(SPI) – soft ion source was designed in this thesis. Under the optimal conditions, a mass resolution of 1200(fwhm) at m/z 78 and the limit of detection(LOD) of benzene of down to 0.1 ppm with directly capillary sampleing were obtained.A spiral tube membrane enrichment system with rapid water cooling technique was designed to improve the sensitivity of portable SPI-TOFMS. Based on the principles of dissolution and diffusion of VOCs in PDMS membrane, the parameters of membrane inlet, such as release temperature, the flow rate of gas, and trap time were optimized. It was found that C6H6, C7H8, and C8H10 obtained with the membrane inlet were highly improved by a factor of 2.1, 71.8 and 157.7, respectively, compared to directly capillary sampling method. The LODs for C6H6, C7H8, and C8H10 were 3 ppb,6 ppb and 6 ppb, respectively. The linear correlation coefficient of the three compounds were more than 0.99 in a certain concentration range. As a result, the portable SPI-TOFMS with the new membrane inlet could satisfy the standard of detection of benzene series compounds in room air due to the high sensitivity.A windowless RF discharge ionization source with the krypton discharging gas, was designed to detect the trace level chlorobenzenes in exhaust gas during waste incineration. Compared to the traditional VUV-lamp-based ion sources, It not only improved the photon flux of about 1 × 1015 photons/s, but also avoided the pollution of lamp window. The parameters of the flow rate of discharge gas and the ionization pressure were optimized and a Tenax Ta absorbent tube based enrichment device was utilized to further increase the sensitivity. It was found that from the continuous monitoring result for 6 h, the relative standard deviations(RSD) of signal intensities for monochlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene were obtained as 7.5%, 5.8% and 11.1%, respectively. The linear response of 0.5-50 ng/L, 0.64-65 ng/L and 0.8-80 ng/L for monochlorobenzene, 1,3-dichlorobenzene and 1,2,4-trichlorobenzene, with limit of detections(S/N>10) of 6.4 pg/L, 9.7 pg/L and 15.2 pg/L, respectively. Due to its good performance, our new designed windowless RF discharge TOFMS, has a huge potential for on-line monitoring of typical precursors of dioxin in the exhaust gas during waste incineration.The windowless RF discharge ion source was applied to explore the change trends of products during the grains fermentation process. The temperature, flow rate of fermentation gas, and the intensities of compounds were recorded during continuous monitoring of fermentation process for 10 days. We also discussed the influences of the three factors and concentrations of compounds in different stages effect on the formation of fermented products and the wine quality. It is implied that this online monitoring technology could be applied to improve the brewing technology and the quality of the wine.