Photoionization-Generated Dibromomethane Cation Chemical Ionization Source for Time-of-Flight Mass Spectrometry and Its Application on Sensitive Detection of Volatile Sulfur Compounds

Abstract

Soft ionization mass spectrometry is one of the key techniques for rapid detection of trace volatile organic compounds. In this work, a novel photoionization-generated dibromomethane cation chemical ionization (PDCI) source has been developed for time-of-flight mass spectrometry (TOFMS). Using a commercial VUV lamp, a stable flux of CH2Br2(+) was generated with 1000 ppmv dibromomethane (CH2Br2) as the reagent gas, and the analytes were further ionized by reaction with CH2Br2(+) cation via charge transfer and ion association. Five typical volatile sulfur compounds (VSCs) were chosen to evaluate the performance of the new ion source. The limits of detection (LOD), 0.01 ppbv for dimethyl sulfide and allyl methyl sulfide, 0.05 ppbv for carbon disulfide and methanthiol, and 0.2 ppbv for hydrogen sulfide were obtained. Compared to direct single photon ionization (SPI), the PDCI has two distinctive advantages: first, the signal intensities were greatly enhanced, for example more than 10-fold for CH3SH and CS2; second, H2S could be measured in PDCI by formation [H2S + CH2Br2](+) adduct ion and easy to recognize. Moreover, the rapid analytical capacity of this ion source was demonstrated by analysis of trace VSCs in breath gases of healthy volunteers and sewer gases.

Vacuum-Ultraviolet-Excited and CH2Cl2/H2O-Amplified Ionization-Coupled Mass Spectrometry for Oxygenated Organics Analysis

“…Interestingly, both cations and anions were simultaneously produced from neutral molecules using an insufficient photon energy, which is different from photoionization and chemical ionization processes. In addition, the ionization process is different from the dopant-assisted atmospheric pressure and low-pressure photoionization pathways, which dope with a photoionizable compound with a high ionization efficiency to facilitate the formation of reagent ions and the subsequent ion–molecule reaction to produce analyte ions. − …”

Automated, high frequency, on-line dimethyl sulfide measurements in natural waters using a novel “microslug” gas-liquid segmented flow method with chemiluminescence detection

“…These GC based techniques involve bulky instrumentation, require controlled laboratory settings and have a relatively low sample throughput, which restricts the ability to make near-continuous measurements [17,18]. Techniques such as membrane inlet mass spectrometry (MIMS) [19], equilibrator inlet proton transfer reaction mass spectrometry (EI-PTRMS) [20][21][22] and atmospheric pressure chemical ionization-mass spectrometry (AP-CIMS) [23,24] have become attractive for real-time DMS analysis on research vessels. However, these devices are relatively heavy, fragile, expensive and labor intensive to deploy on a ship.…”

Measurement of CS2 Absorption Cross-Sections in the 188–215 nm Region at Room Temperature and Atmospheric Pressure

“…Many methods have been established to detect CS 2 concentration including chemical sensors, mass spectrometry, laser spectroscopy and differential optical absorption spectroscopy. 10–13 Among them, the detection methods based on differential optical absorption spectroscopy are well suitable for measuring CS 2 concentration because CS 2 has strong absorption lines in the ultraviolet (UV) region due to the electron transitions, and has advantages of high sensitivity and short response time. The measurement of CS 2 concentration has been intensively investigated using differential absorption spectroscopy.…”