Knighton W B, Fortner E C, Herndon S C, Wood E C, Miake-Lye R C
Department of Chemistry and Biochemistry, Montana State University-Bozeman, Bozeman, MT 59717, USA.
Rapid Commun Mass Spectrom. 2009 Oct 30;23(20):3301-8. doi: 10.1002/rcm.4249.
A proton transfer reaction mass spectrometer (PTR-MS) instrument was adapted to employ NO+ as a chemical reagent ion without any hardware changes by switching the reagent ion source gas from water vapor to dry air. Ionization of dry air within the hollow cathode ion source generates a very intense source of NO+ with only a minor impurity of NO2+. The intensities of the primary NO+ reagent ion and the unwanted impurity NO2+ are controllable and dependent on the operational conditions of the hollow cathode ion source. Ion source tuning parameters are described, which maintain an intense source of NO+ while keeping the impurity NO2+ signal to less than 2% of the total reagent ion intensity. This method is applied to the detection of 1,3-butadiene. NO+ reacts efficiently with 1,3-butadiene via a charge exchange reaction to produce only the molecular ion, which is detected at m/z 54. Detection sensitivities of the order of 45 pptv for a 1-s measurement of 1,3-butadiene are demonstrated. We present the first real-time on-line sub parts per billion measurement of 1,3-butadiene in the ambient atmosphere. The only likely interference is from 1,2-butadiene. Concurrent measurements of benzene are provided and suggest that the vehicular emissions are the predominant source of 1,3-butadiene in a suburban Boston area monitoring location.
通过将试剂离子源气体从水蒸气切换为干燥空气，质子转移反应质谱仪（PTR-MS）在无需任何硬件更改的情况下，被改造为使用NO⁺作为化学试剂离子。空心阴极离子源内干燥空气的电离产生了非常强烈的NO⁺源，仅含有少量的NO₂⁺杂质。主要的NO⁺试剂离子和不需要的杂质NO₂⁺的强度是可控的，并且取决于空心阴极离子源的运行条件。文中描述了离子源调谐参数，这些参数可维持强烈的NO⁺源，同时使杂质NO₂⁺信号低于总试剂离子强度的2%。该方法应用于1,3 - 丁二烯的检测。NO⁺通过电荷交换反应与1,3 - 丁二烯高效反应，仅产生在m/z 54处检测到的分子离子。对于1,3 - 丁二烯1秒的测量，展示了约45 pptv的检测灵敏度。我们首次实现了对环境大气中1,3 - 丁二烯的实时在线十亿分率以下的测量。唯一可能的干扰来自1,2 - 丁二烯。文中还提供了苯的同步测量结果，并表明在波士顿郊区一个监测地点，车辆排放是1,3 - 丁二烯的主要来源。
