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

Single-photon ionization (SPI) is a unique soft ionization technique for 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 an ordinary electrodeless fluorescent lamp. By replacing the glass bulb with a stainless steel bulb and introducing 5% Kr/He (v/v) as the excitation gas, an excellent VUV photon flux over 4.0 × 1014 photons s-1 was obtained. Due to its rapid glow characteristics, the VUV lamp can be switched on and off instantly as required by detection, ensuring the stability and service life of the lamp. To demonstrate the performance of the new lamp, the switchable VUV lamp was coupled with an SPI-mass spectrometer, which could be changed to photoinduced associative ionization (PAI) mode by doping gaseous CH2Cl2 to initiate an associative ionization reaction. Two types of volatile organic compounds sensitive to SPI and PAI, typically benzene series and oxygenated organics, respectively, were selected as samples. The instrument exhibited a high detection sensitivity for the tested compounds. With a measurement time of 11 s, the 3σ limits of detection ranged from 0.33 to 0.75 pptv in SPI mode and from 0.03 to 0.12 pptv in PAI mode. This study provides an 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 highly sensitive detection technologies.

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

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 × 1014 and ∼9.80 × 1012 photons s-1, respectively, while their corresponding leakage flow rates of the discharge gas are 0.062 and 0.046 cm3 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 (CH3Cl), methylene chloride (CH2Cl2), trichloromethane (CHCl3), and carbon tetrachloride (CCl4) 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 high-energy EUV light, with many application prospects in scientific research.

Real-time emission characteristics, health risks, and olfactory effects of VOCs released from soil disturbance during the remediation of an abandoned chemical pesticide industrial site.

Volatile organic compounds (VOCs) released along with soil disturbance during the remediation of abandoned industrial sites have attracted great attention due to their possible toxicity and odour. However, the real-time emission characteristics of these VOCs and their subsequent effects on health and olfaction are less understood. In this study, the gaseous VOCs released from soil disturbance by excavators and drilling rigs at an abandoned chemical pesticide plant were monitored online with a laboratory-built single photoionization time-of-flight mass spectrometer (SPI-TOFMS). Twelve main VOCs with total mean concentrations ranging from 2350 to 3410 µg m-3 were observed, with dichloromethane (DCM) having a significant contribution. The total concentrations of the remaining 11 VOCs increased substantially during soil disturbance, with the total mean concentrations increasing from 18.65-39.05 to 37.95-297.94 µg m-3 and those of peak concentrations increasing from 28.46-58.97 to 88.38-839.13 µg m-3. This increase in VOC concentrations during soil disturbance leads to an enhanced heath risk for on-site workers. The distinctive difference between the mean and peak concentrations of VOCs indicates the importance of using mean and peak concentrations, respectively, for risk and olfactory evaluation due to the rapid response of the human nose to odours. As a result, the cumulative noncarcinogenic risk at the relatively high pollutant plot was higher than the occupational safety limit, while the total carcinogenic risks at all monitored scenarios exceeded the acceptable limit. Among the VOCs investigated, DCM and trichloroethylene (TCE) were determined to be crucial pollutants for both noncarcinogenic and carcinogenic risks of VOCs. With regard to olfactory effects, organic sulphides, including dimethyl disulphide (DMDS), dimethyl sulphide (DMS), and dimethyl trisulphide (DMTS) were identified as dominant odour contributors (78.28-92.11%) during soil disturbance.

Insight into the crucial reason causing the difference in secondary organic aerosol yields of monocyclic aromatic hydrocarbons with different methyl substituent numbers.

The secondary organic aerosol (SOA) yield of toluene photooxidation was reported to substantially higher than that of trimethylbenzene due to the effect of the number of methyl substituents. However, the intrinsic mechanism for this disparity is not clear enough. In this study, a highly-sensitive thermal-desorption photoinduced associative ionization mass spectrometer (TD-PAI-MS) was used to real-time characterize the molecular composition and its evolution of the SOA generated from the photooxidation of toluene and 1,2,3-trimethylbenzene (1,2,3-TMB) in a smog chamber. In the new particle formation (NPF) stage, toluene generated more variety of nucleation precursors, such as benzaldehyde (MW 106) and benzoic acid (MW 122), resulting in a much higher nucleation rate and SOA number concentration. In the SOA growth/aging stage, the key SOA components of toluene were mainly dialdehydes, e.g., 2-oxopropanedial (MW 86) and 4-oxopent-2-enedial (MW 112), which played an important role in the formation of highly oxidized species (HOS) through oligomerization or cyclization reactions. In contrast, due to the presence of more methyl groups, 1,2,3-TMB was inclined to produce ketones, e.g., 2,3-butanedione (MW 86) and 3-methyl-4-oxopent-2-enal (MW 112), which would be cleaved into high-volatility low molecular compounds, e.g., acetic acid, through fragmentation. Taken together, relative to 1,2,3-TMB, the higher nucleation rate during NPF and the significant oligomerization/functionalization process during SOA growth are thought to be the major reasons resulting in the higher SOA yield of toluene. This work provides a reference for the insight into the different SOA yields of monocyclic aromatic hydrocarbons (MAHs) through further revealing the SOA formation mechanism during toluene and 1,2,3-TMB photooxidation.

Direct detection of acetonitrile at the pptv level with photoinduced associative ionization time-of-flight mass spectrometry.

Photoionization mass spectrometry (PI-MS) has become a versatile tool in the real-time analysis of volatile organic compounds (VOCs) from the atmosphere or exhaled breath. However, some key species, e.g., acetonitrile, are hard to measure due to their higher ionization energies than photon energy. In this study, the direct and sensitive detection of gaseous acetonitrile based on a photoinduced associative ionization (PAI) reaction was investigated with a laboratory-built PAI time-of-flight mass spectrometer (PAI-TOFMS). By doping CH2Cl2 in the photoionization ion source, the mass signal of acetonitrile that cannot be effectively obtained by photoionization appeared with an extremely high intensity through the PAI reaction between acetonitrile, CH2Cl2, and residual H2O in the system. Though the moisture in the sample gas has an evident impact on the detection efficiency of acetonitrile, with a relative signal intensity decreasing from 100% under dry conditions to 60% at saturated relative humidity, excellent detection sensitivity was still obtained for gaseous acetonitrile in different matrixes. The sensitivity calibration experiment showed that the detection sensitivities of acetonitrile in N2 buffer gas, exhaled gas, and outdoor air were 682.4 ± 5.2, 17.0 ± 0.7, and 23.9 ± 0.2 counts pptv-1, respectively, with an analysis time of 10 s. The corresponding 3σ LODs reached 0.22, 8.82, and 6.28 pptv, which are equivalent to 0.40, 16.0, and 11.4 ng m-3. The performance of the PAI-TOFMS was first demonstrated by analyzing exhaled acetonitrile from healthy non-smokers and smokers and continuous monitoring of acetonitrile in outdoor air. In summary, this study provides a new and highly sensitive method for the real-time detection of acetonitrile through mass spectrometry.