A Simple High-Flux Switchable VUV Lamp Based on an Electrodeless Fluorescent Lamp for SPI/PAI Mass Spectrometry

Single-photon ionization (SPI) isa unique soft ionizationtechniquefor organic analysis. A convenient high-flux vacuum ultraviolet (VUV)light source is a key precondition for wide application of SPI techniques.In this study, we present a novel VUV lamp by simply modifying anordinary electrodeless fluorescent lamp. By replacing the glass bulbwith a stainless steel bulb and introducing 5% Kr/He (v/v) as theexcitation gas, an excellent VUV photon flux over 4.0 x 10(14) photons s(-1) was obtained. Due to its rapidglow characteristics, the VUV lamp can be switched on and off instantlyas required by detection, ensuring the stability and service lifeof the lamp. To demonstrate the performance of the new lamp, the switchableVUV lamp was coupled with an SPI-mass spectrometer, which could bechanged to photoinduced associative ionization (PAI) mode by dopinggaseous CH2Cl2 to initiate an associative ionizationreaction. Two types of volatile organic compounds sensitive to SPIand PAI, typically benzene series and oxygenated organics, respectively,were selected as samples. The instrument exhibited a high detectionsensitivity for the tested compounds. With a measurement time of 11s, the 3 & sigma; limits of detection ranged from 0.33 to 0.75 pptvin SPI mode and from 0.03 to 0.12 pptv in PAI mode. This study providesan extremely simple method to assemble a VUV lamp with many merits,e.g., portability, robustness, durability, low cost, and high flux.The VUV lamp may contribute to the development of SPI-related highlysensitive detection technologies.