单光子/光电子在线质谱实时分析聚氯乙烯热分解/燃烧产物

Real-Time Analysis of Polyvinyl Chloride Thermal Decomposition/Combustion Products with Single Photon Ionization/Photoelectron Ionization Online Mass Spectrometer

实验室研制了低能光电子磁场增强电离(MEPEI)和单光子电离(SPI)复合电离源,该电离源具有电离化合物范围宽、碎片离子少、质谱图简单等优点,结合飞行时间质谱(TOF-MS)实现了聚氯乙烯(PVC)热分解/燃烧产物的在线分析.针对不同的目标化合物,MEPEI/SPI复合电离源通过调节电离区电场强度,可以快速在SPI和SPI-MEPEI之间切换.PVC热分解/燃烧产物中电离能大于光子能量(10.60 eV)的HCl和CO2(12.74 eV、13.77 eV)利用MEPEI模式电离;而烯烃、二氯乙烯、苯系物、氯苯、苯乙烯、茚满及萘系物等可通过SPI-MEPEI复合模式电离.通过实时监测PVC主要燃烧产物的信号强度随温度的变化趋势可推断出,PVC燃烧产物主要是通过两种机制生成:①250～370℃时,PVC发生脱氯及分子内环化反应,产生大量的HCl、苯和萘;②380～510℃时,PVC发生分子间交联反应,生成烷基芳烃,如甲苯和二甲苯/乙苯等.实验结果表明,SPI/SPI-MEPEI复合离子源TOF-MS分析速度快,应用范围广,在在线分析中具有广泛的应用前景.

With the features of a broad range of ionizable compounds,reduced fragments and simple mass spectrum,a homemade magnetic field enhanced photoelectron ionization（MEPEI） source combined with single photon ionization（SPI） for time-of-flight mass spectrometer was built and applied to analyze thermal decomposition/combustion products of polyvinyl chloride（PVC）.The combined ion source can be switched very fast between SPI mode and SPI-MEPEI mode for detecting different targeted compounds,and only adjusting the voltage of the electrode in the ionization region to trigger the switch.Among the PVC thermal decomposition/combustion products,HCl and CO2,which ionization energies（12.74 eV,13.77 eV respectively） were higher than the energy of photon（10.60 eV）,were ionized by MEPEI,while alkenes,dichloroethylene,benzene and its homologs,monochlorobenzene,styrene,indane,naphthalene and its homologs were ionized by SPI and MEPEI simultaneously.Spectra of interested products as a function of temperatures indicated that products are formed via two main mechanisms：（1） dechlorination and intramolecular cyclization can lead to the formation of HCl,benzene and naphthalene at 250-370℃;（2） intermolecular crosslinking leads to the formation of alkyl aromatics such as toluene and xylene/ethylbenzene at 380-510℃.The experimental results show that the combined ion source of SPI/SPI-MEPEI for TOF-MS has broad application prospects in the online analysis field.