Novel MCP-Windowed EUV Light Source and Its Mass Spectrometric Application for Detecting Chlorinated Methanes

Abstract

Various vacuum ultraviolet (VUV) lamps are simple and convenient VUV light sources for mass spectrometry and other research fields. However, the strong absorption of high-energy photons by window materials limits the application of an extreme ultraviolet (EUV) light. In this study, a novel high-flux EUV light source is developed using a microchannel plate (MCP) window to transmit 73.6 nm (16.9 eV) EUV light generated via the radio frequency (RF) inductive discharge of neon. The MCP used is a 0.5 mm thick glass plate with a regular array of microtubes (12 μm i.d.). The photon fluxes of the EUV light source with the MCP window (12 mm i.d.) and an aperture (1.8 mm i.d.) are ∼1.31 × 10 14 and ∼9.80 × 10 12 photons s −1 , respectively, while their corresponding leakage flow rates of the discharge gas are 0.062 and 0.046 cm 3 atom s −1 , according to the contrast experiments. The transmission efficiency of the MCP to the EUV light is 30.2%, with a 1.2% deviation. An EUV photoionization time-of-flight mass spectrometer (EUV-PI-TOFMS) is built to validate the practicality of the MCP-windowed EUV light source further. The detection sensitivities in 30 s measurements for methyl chloride (CH 3 Cl), methylene chloride (CH 2 Cl 2 ), trichloromethane (CHCl 3 ), and carbon tetrachloride (CCl 4 ) in synthetic air are 4366, 4120, 5854, and 4095 counts ppbv −1 , respectively. The corresponding 3σ limits of detection (LODs) are 42, 34, 24, and 15 pptv. This study develops a new feasible method for efficiently utilizing highenergy EUV light, with many application prospects in scientific research.

Pressure-Driven Switching of Photoelectron Impact Ionization-Chemical Ionization/Penning Ionization in Vacuum Ultraviolet Photoionization Mass Spectrometry

“…Vacuum ultraviolet photoionization mass spectrometry (VUV-PI MS) is a powerful analytical method due to its soft ionization property of organic species. VUV-PI MS has been successfully applied in diverse fields such as environmental exposure, food safety, and chemical processes. − Among the light sources applied in VUV-PI MS including VUV lamp-based light sources, − laser-based light sources, , and synchrotron radiation light sources, , low-pressure discharge lamps filled with different rare gases have attracted widespread interest due to their compactness and low cost, and the krypton (Kr) lamp has become one of the most commonly used light sources for single photoionization (SPI). − Unfortunately, the relatively low photon flux of the VUV Kr lamp restricted the sensitivity, and the detection of analytes with high ionization energy (IE) was challenging owing to the fixed photon energies of 10.0 and 10.6 eV.…”