title: Protonation enhancement by dichloromethane doping in low-pressure photoionization.
abstract: Doping has been used to enhance the ionization efficiency of analytes in atmospheric pressure photoionization, which is based on charge exchange. Compounds with excellent ionization efficiencies are usually chosen as dopants. In this paper, we report a new phenomenon observed in low-pressure photoionization: Protonation enhancement by dichloromethane (CH2Cl2) doping. CH2Cl2is not a common dopant due to its high ionization energy (11.33 eV). The low-pressure photoionization source was built using a krypton VUV lamp that emits photons with energies of 10.0 and 10.6 eV and was operated at ~500-1000 Pa. Protonation of water, methanol, ethanol, and acetaldehyde was respectively enhanced by 481.7 ± 122.4, 197.8 ± 18.8, 87.3 ± 7.8, and 93.5 ± 35.5 times after doping 291 ppmv CH2Cl2, meanwhile CH2Cl2almost does not generate noticeable ions itself. This phenomenon has not been documented in the literature. A new protonation process involving in ion-pair and H-bond formations was proposed to expound the phenomenon. The observed phenomenon opens a new prospect for the improvement of the detection efficiency of VUV photoionization.
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.|Shanghai Masteck Environment Co., Ltd, Shanghai, China.
authors.forename: Jinian
authors.initials: J
authors.lastname: Shu
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Zou
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Ce
authors.initials: C
authors.lastname: Xu
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Li
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Wanqi
authors.initials: W
authors.lastname: Sun
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Haixu
authors.initials: H
authors.lastname: Zhang
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: State Key Joint Laboratory of Environment Simulation and Pollution Control, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.|University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Pengkun
authors.initials: P
authors.lastname: Ma