无窗射频放电单光子电离质谱在线监测氯苯的研究

On-Line Analysis of Cholrobenzenes by Windowless RF Discharge Signal Photon Ionization Mass Spectrometer

氯苯类化合物是垃圾焚烧烟气中二噁英的主要前生体之一,可以作为二噁英在线监测的指示物。本工作采用自行研制的高光子密度的无窗射频放电单光子软电离飞行时间质谱,结合自动富集解析系统对垃圾焚烧烟气中低浓度的氯苯类化合物的在线快速检测进行研究。以氪气为放电气体的无窗射频放电光电离源,替代了商品化的真空紫外（VUV）灯光电离源,既提高了光子的发射效率,又避免了光窗污染。实验结果表明,在单个检测周期内（36min）,采用填装200mg Tenax TA的吸附管对样品预富集10 min,一氯苯、1,3-二氯苯、1,2,4-三氯苯3种物质的线性范围分别为0.5~50、0.64~65、0.8~80ng/L,检测限分别达到6.4、9.7、15.2pg/L（S/N〉10）;在6h连续监测结果中,3种氯苯类化合物的信号强度相对标准偏差（RSD）分别为7.5%、5.8%、11.1%。该仪器对垃圾焚烧烟气中二噁英主要前生体的在线监测具有很大的应用潜力,该方法可为氯苯类化合物的在线自动化检测奠定基础。

Chlorobenzenes（CBs）,one of the typical precursors of dioxin in the exhaust gas during waste incineration,can be considered as the indicators for on-line monitoringof dioxin.Based on windowless RF discharge,a single photon ionization time-of-flight mass spectrometer with high photon density was designed to detect the chlorobenzenes with low concentrations in exhaust gas during waste incineration.With the combination of automatic trap and release system,the on-line and rapid detection of chlorobenzenes was investigated.With krypton as the discharge gas,windowless RF discharge photoionization source was employed instead of commercial vacuum ultraviolet（VUV）lamp,which not only improved the radiation efficiency of photons as well as the sensitivity of instrument,but also avoided the pollution of lamp window.In the single measurement period of 36 min,a TA trap tube that filled with 200 mg Tenax was used to implement the sample preconcentration for 10 min,resulting in the linear response ranges of0.5-50,0.64-65 and 0.8-80ng/L for monochlorobenzene,1,3-dichlorobenzene and1,2,4-trichlorobenzene,with limit of detections（S/N〉10）of 6.4,9.7and 15.2pg/L,respectively.From the continuous monitoring result for 6h,the relative standard deviations（RSD）of signal intensities for monochlorobenzene,1,3-dichlorobenzene and1,2,4-trichlorobenzene are obtained to 7.5%,5.8% and 11.1%,respectively,demonstrating the good stability of windowless RF discharge single photon ionization timeof-flight mass spectrometer,which can be applied in the on-line monitoring of typical precursors of dioxin in the exhaust gas during waste incineration dioxin.