Furuya Hiroko, Fujimaki Susumu, Kambara Shizuka, Suzuki Shigeo, Hashimoto Yutaka, Okazaki Shigemitsu, Wada Akira, Beech Iwona B, Sunner Jan, Hiraoka Kenzo
Clean Energy Research Center, University of Yamanashi, Takeda-4, Kofu 400-8511, Japan.
Rapid Commun Mass Spectrom. 2005;19(17):2433-42. doi: 10.1002/rcm.2085.
Atmospheric pressure Penning ionization mass spectra of methanol were measured as functions of Ar or He gas pressure in the first vacuum chamber, the position of the skimmer, and the voltage applied between the orifice and the skimmer. When the orifice and the skimmer were coaxial with a distance of 4 mm, the distribution of CH3OH2+(CH3OH)n clusters was only weakly dependent on both Ar pressure (in the range of 19-220 Pa) and orifice-skimmer voltage (in the range of 1-45 V). The ion/molecule reaction CH3OH2+ + CH3OH --> CH3+(CH3OH) + H2O was observed in the free jet expansion, especially at high orifice-skimmer voltage values. When the orifice and the skimmer were off-centered and the distance between them was increased to 18 mm, the formation of large CH3OH2+(CH3OH)n clusters, as well as their dissociation, were seen. The endothermic proton transfer reaction, CH3+(CH3OH) + CH3OH --> CH3OH2+ + CH3OCH3, occurred at high orifice-skimmer voltage. The collision-induced dissociation of cluster ions by He gas in the first vacuum chamber was much more efficient than by Ar. These results demonstrated that the mass spectra are highly dependent on skimmer position and on orifice-skimmer voltage and that ions observed by mass spectrometry do not necessarily reflect the abundance of ions produced in the atmospheric pressure ion source.
测量了甲醇的大气压彭宁电离质谱，它是第一真空室中氩气或氦气压力、撇油器位置以及孔板与撇油器之间施加电压的函数。当孔板和撇油器同轴且距离为4毫米时，CH3OH2+(CH3OH)n簇的分布仅微弱地依赖于氩气压力（在19 - 220帕范围内）和孔板 - 撇油器电压（在1 - 45伏范围内）。在自由射流膨胀中观察到离子/分子反应CH3OH2+ + CH3OH --> CH3+(CH3OH) + H2O，特别是在高孔板 - 撇油器电压值时。当孔板和撇油器偏心且它们之间的距离增加到18毫米时，可以看到大的CH3OH2+(CH3OH)n簇的形成及其解离。吸热质子转移反应CH3+(CH3OH) + CH3OH --> CH3OH2+ + CH3OCH3在高孔板 - 撇油器电压下发生。第一真空室中氦气对簇离子的碰撞诱导解离比氩气更有效。这些结果表明，质谱高度依赖于撇油器位置和孔板 - 撇油器电压，并且质谱法观察到的离子不一定反映大气压离子源中产生的离子丰度。
