质子转移反应质谱的建立与性能研究

Development and Validation of Proton Transfer Reaction Mass Spectrometry

报道了自行研制的质子转移反应质谱的基本结构和性能。利用水蒸气辉光放电产生了反应离子H3O+,以合成空气为反应气体,测量了H3O+与合成空气中的水反应产生的团簇离子H3O+(H2O)n的质谱。实验发现,当漂移管电场与分子密度比值为144Td时,增加的离子能量可以阻止团簇离子H3O+(H2O)n的形成,质谱观察到的离子主要是H3O+,其纯度可达99%以上,这时H3O+与有机物分子如甲苯的质子转移反应的产物离子也呈单一形式,团簇离子得到很好地抑制。根据离子强度和离子反应时间等参数,获得了PTR-MS目前的检出限为10-8(V/V)。利用PTR-MS对标准浓度甲苯及其稀释气体进行检测,表明PTR-MS在线定量检测准确性良好,线性动态范围跨越3个数量级,能够应用于大气中痕量挥发性有机物的实时在线测量。

The construction and performance study is reported for a newly developed proton transfer reaction mass spectrometry （PTR-MS）. The primary ions H3O^＋ was generated using a glow discharge through water vapor. Synthetic air was used as reagent gas so as to optimize the ionic collision energy via the ratio of electric field intensity and neutral gaseous number density （E/N） in the drift tube. The protonated water cluster ions were found to reduce to the ion form of H3O^＋ with purity above 99% when the E/N was set to be144Td. With such a value of E/N, the organic compound, like toluene, also exhibited single ionic mass spectrometric peak due to the proton transfer reaction with H3O^＋ , and the formation of proton bound cluster ions containing H2O molecules could be efficiently forbidden. The limit of detection of the homemade PTR-MS was around 10×10^-9 （V/V） based on the primary ion intensity, ion reaction time and instrumental parameters. The toluene standard gas was determined quantitatively. It indicats that the PTR-MS has a good accuracy and stability for on-line measurement of trace volatile organic compounds. The linear dynamics range of detection is over three orders of magnitude. This system allows real-time measurements of volatile organic compounds （VOCs） in air.