Symmetric Atmospheric Plasma Source Integrated With Electrospray Ionization for Ambient Mass Spectrometry Detections

This paper develops a symmetric atmospheric plasma source integrated with electrospray ionization (ESI) tip as a dual-ion source for simultaneously detecting nonpolar and polar compounds using the ambient mass spectrometry. A cross-shaped tube with symmetric discharge electrodes is used to generate dielectric barrier discharge to produce ionized gas charging nonpolar molecules, while a coaxial capillary is placed at the center of the cross-shaped tube for generating electrospray discharge. Since there is no floating voltage at the outlet of the cross-shaped tube, the potential interference for the ESI can be excluded. Results show that dual-ion source can stably produce high-intensity ions of 10
⁹
ion · cm
^-3
. Moreover, the relationship between the measured ion intensity and the gas flow rate, gas temperature, and applied voltage for ESI are systematically investigated. Various samples including volatile organic compounds, pesticides, Chinese herbal medicines, and vitamins are used for evaluating the sensing performance of the dual-ion source in plasma mode, electrospray mode, and dual-ion source mode, respectively. Results show that the developed dual source is efficient to simultaneously detect both the polar and nonpolar compounds.