Vacuum Ultraviolet Single Photon Ionization Research Articles

Thermal decomposition and isomerization of 1-Butyl and 1-Pentyl radical by flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry.

Thermal decomposition and isomerization of 1-butyl and 1-pentyl radical were studied in the temperature range of 500-1480 K on a short time scale of 20-100 µs using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry. 1-Bromobutane and 1-bromopentane were used as precursors for the 1-butyl and 1-pentyl radical, respectively. The reactive intermediates in the thermal dissociation reactions were directly observed. The 1-butyl radical decomposed to ethene and ethyl radical with ethyl radical rapidly losing an H atom to form a second ethene molecule. Loss of H atom from butyl radical was also a significant decomposition channel. Isomerization of 1-butyl via 1,3-H migration was observed as a minor channel at 1380 K and above with a branching ratio of less than 3% at 1430 K. The 1-pentyl radical was observed to decompose mainly by isomerization to 2-pentyl radical followed by β-scission to produce propene and ethyl radicals at temperatures approximately 900 K and below. Above 900 K, β-scission of 1-pentyl to produce ethene and 1-propyl radical became increasingly important. Isomerization to 3-pentyl was verified to be a minor channel.

Investigation of pyruvic acid photolysis at the air-liquid interface as a source of aqueous secondary organic aerosols

Pyruvic acid (PA) is a ubiquitous 2-oxocarboxylic acid in the atmosphere. Its photochemical process at the air-liquid (a-l) interface has been suggested as an important source of aqueous secondary organic aerosols. We investigated the photochemical reaction pathways of PA at the a-l interface using synchrotron-based vacuum ultraviolet single-photon ionization mass spectrometry (VUV SPI-MS) coupled with the System for Analysis at the Liquid Vacuum Interface (SALVI) microreactor. Results from mass spectral analysis and the determination of appearance energies (AEs) indicate that photolysis of PA can generate radicals, then they recombine with carboxylic acids and simple molecular oligomers. Furthermore, the preliminary products could form larger oligomers via radical reaction or esterification in the presence of hydroxyl and carboxyl functional groups. Mass spectral comparison shows that most photochemical reactions would complete within 4 h. The expanded photochemistry-driven reaction flowchart of PA is proposed based on the newly discovered products. Our results reveal that the interfacial PA photochemical reactions have different mechanisms from the bulk liquid due to the interfacial properties, such as molecular density, composition, and ion concentration. Our findings show that in situ mass spectral analysis with bright photon ionization is useful to elucidate the contribution of a-l interfacial reactions leading to aqSOA formation.

Vacuum Ultraviolet Single Photon Ionization and Decomposition of 2-Aminopropionitrile in Astrophysical Objects

The molecule 2-aminopropionitrile (2-APN; H3CCH(NH2)CN) is a chiral precursor of the amino acid alanine and could play an important role in the emergence of the homochirality of life. To date, 2-APN has not yet been detected in the interstellar medium. To address the question of its absence, possibly through destruction by vacuum ultraviolet radiation in astrophysical media, we studied its photoionization and dissociative photoionization in the 9–14 eV (89–137 nm) energy range using photoelectron–photoion coincidence spectroscopy with velocity map imaging. Density functional theory calculations were performed at the PBE0/aug-cc-pVTZ level to determine structures for the various cationic fragments identified experimentally. Their appearance energies were calculated. The adiabatic ionization energy (AIE) of 2-APN is AIE = (9.85±0.01) eV and the appearance energy (AE) of the major fragment ion N≡CC(H)NH2 + is AE = (10.57±0.01) eV. Both ions, 2-APN+ and N≡CC(H)NH2 +, make up more than 90% of the formed ions. N≡CC(H)NH2 +, an isomer of the protonated HCN dimer, is also formed with high yield in the dissociative photoionization of aminoacetonitrile (NH2CH2CN), another α-aminonitrile observed in Sgr B2(N). Photoion yield spectra have been calibrated to absolute ionization cross sections. From these, we derive photoionization rates in several typical radiation fields relevant to different astrophysical objects. The rates show that, under almost all explored radiation fields, dissociative ionization is the dominant pathway for photoionization, leading to the loss of a methyl group (CH3) to form the planar thermodynamically stable amino cyano methylidynium ion N≡CC(H)NH2 +. The observed absence of 2-APN in Sgr B2 could thus be due to dominant dissociative photoionization.

Understanding the Reaction Chemistry of 1,1,3,3-Tetramethyldisilazane as a Precursor Gas in a Catalytic Chemical Vapor Deposition Process.

The reaction chemistry of 1,1,3,3-tetramethyldisilazane (TMDSZ) in catalytic chemical vapor deposition (Cat-CVD), including its primary decomposition on a heated W filament and secondary gas-phase reactions in a Cat-CVD reactor, was studied using 10.5 eV vacuum ultraviolet single-photon ionization and/or laser-induced electron ionization in tandem with time-of-flight mass spectrometry. It has been demonstrated that TMDSZ initially breaks down to form various species, including methyl radical (•CH3), ammonia (NH3), and 1,1-dimethylsilanimine (DMSA). The activation energies (Ea) for the formation of •CH3 and NH3 were determined to be 61.2 ± 1.0 and 42.1 ± 0.9 kJ mol-1, respectively, in the temperature range of 1400-2000 and 900-2400 °C. It was found that the formation of DMSA may have two different contributing routes, i.e., a concerted one (Ea = 33.6 ± 2.3 kJ mol-1) at lower temperatures of 900-1500 °C and a stepwise one (Ea = 155.0 ± 7.8 kJ mol-1) at higher temperatures of 2100-2400 °C. The secondary gas-phase reactions occurring in the Cat-CVD reactor environment were found to stem from two competing processes. The first one, free-radical short-chain reactions initiated by •CH3 formation and propagated by H abstraction reactions, is the dominating chemical process, producing many high-mass stable alkyl-substituted or silyl-substituted disilazane or trisilazane products via radical recombination reactions. Head-to-tail cycloaddition of unstable DMSA is the second contributing chemical process, which forms cyclodisilazane species. In addition, evidence was found for the conversion of NH3 into H2 and N2 in the Cat-CVD reactor.

Effect of Fe2O3 on the pyrolysis of two demineralized coal using in-situ pyrolysis photoionization time-of-flight mass spectrometry

Influence of Fe2O3 on the pyrolysis products distribution of demineralized Hongshaquan (HSQ) and Daliuta (DLT) coal was investigated by a novel in-situ pyrolysis vacuum ultraviolet single photon ionization time-of-flight mass spectrometry. The experiment samples were obtained by mechanical mixing of Fe2O3 and demineralized coal from acid elution with the mass ratio of 10:1, 5:1 and 2:1. Due to the characteristics of in-situ sampling, soft ionization and high vacuum environment, the initial pyrolysis volatiles including alkenes, aromatic hydrocarbons, phenols, bi-phenols and a small amount of sulfur and nitrogen-containing substances can be detected. The results show that Fe2O3 has similar influence on the products distribution of two demineralized coal, and it is relatively stronger on DLT coal than that on HSQ. With the increase of Fe2O3 content, the light fraction content is promoted such as alkenes and aromatic hydrocarbons, but bi-phenols are obviously inhibited. Correspondingly, the heavy products are also decreased, and the evolution peak temperatures of the product increase. Fe2O3 is successively reduced to FeO and Fe while transforming heavy components into light components. The increase of aliphatic carbon (or aromatic hydrocarbon substituted carbon) during coal pyrolysis process is mainly responsible for the decrease pyrolysis peak temperature.

Proton Transfer in Nitromethane-Ammonia Clusters under VUV Single-Photon Ionization Explored by Infrared Spectroscopy and Theoretical Calculations.

It is known that the acidity and reactivity of the CH bond can be enhanced after ionization. Also, this property plays a pivotal role in proton transfer reaction and in the formation of new molecules. Herein, infrared spectroscopy and high-precision quantum chemical calculations are used to study the neutral and cationic clusters of nitromethane-ammonia (CH3NO2-NH3). It is found that in the neutral cluster, CH3NO2 and NH3 are mainly bonded by three intermolecular hydrogen bonds, in which electrostatic contribution plays a major role. After vacuum ultraviolet (VUV) single-photon ionization of CH3NO2-NH3, the positive charge redistributes from the ionized nitrogen atom of NH3 to the CH3NO2 molecule immediately. Then, the proton of CH3NO2 transfers to NH3 to form a proton-transferred type structure CH2NO2-NH4+, without any effective energy barrier, due to the positive hyperconjugation of cationic nitromethane. A closed loop of positive charge transfer takes place in the CH3NO2-NH3 cluster after VUV ionization. The present work demonstrates that both the proton transfer reaction and charge transfer process have occurred in the ionized CH3NO2-NH3 cluster. Moreover, it is found that the proton transfer reaction is a result of the highly acidic CH bond caused by hyperconjugation between the σ (CH) bond and π orbital.

Studying Interfacial Dark Reactions of Glyoxal and Hydrogen Peroxide Using Vacuum Ultraviolet Single Photon Ionization Mass Spectrometry

Aqueous secondary organic aerosol (aqSOA) formation from volatile and semivolatile organic compounds at the air–liquid interface is considered as an important source of fine particles in the atmosphere. However, due to the lack of in situ detecting techniques, the detailed interfacial reaction mechanism and dynamics still remain uncertain. In this study, synchrotron-based vacuum ultraviolet single-photon ionization mass spectrometry (VUV SPI-MS) was coupled with the System for Analysis at the Liquid Vacuum Interface (SALVI) to investigate glyoxal dark oxidation products at the aqueous surface. Mass spectral analysis and determination of appearance energies (AEs) suggest that the main products of glyoxal dark interfacial aging are carboxylic acid related oligomers. Furthermore, the VUV SPI-MS results were compared and validated against those of in situ liquid time-of-flight secondary ion mass spectrometry (ToF-SIMS). The reaction mechanisms of the dark glyoxal interfacial oxidation, obtained using two different approaches, indicate that differences in ionization and instrument operation principles could contribute to their abilities to detect different oligomers. Therefore, the mechanistic differences revealed between the VUV SPI-MS and ToF-SIMS indicate that more in situ and real-time techniques are needed to investigate the contribution of the air–liquid interfacial reactions leading to aqSOA formation.

New Insights into Secondary Organic Aerosol Formation at the Air-Liquid Interface.

Air-liquid interfacial processing of volatile organic compound photooxidation has been suggested as an important source of secondary organic aerosols. However, owing to the lack of techniques for studying the air-liquid interface, the detailed interfacial mechanism remains speculative. To obviate this, we enabled in situ synchrotron-based vacuum ultraviolet single photon ionization mass spectrometry using the system for analysis at the liquid-vacuum interface microreactor to study glyoxal photooxidation at the air-liquid interface. Determination of reaction intermediates and new oxidation products, including polymers and oligomers, by mass spectral analysis and appearance energy measurements has been reported for the first time. Furthermore, an expanded reaction mechanism of photooxidation and free radical induced reactions as a source of aqueous secondary organic aerosol formation is proposed. Single photon ionization can provide new insights into interfacial chemistry.

Thermal decomposition mechanism of allyltrichlorosilane and allyltrimethylsilane

Thermal decomposition of allyltrichlorosilane and allyltrimethylsilane at temperatures up to 1340 K were studied using flash pyrolysis coupled with molecular beam sampling and vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). The initial reaction of allyltrichlorosilane was homolysis of the Si–C bond, producing •SiCl3 and •C3H5 radicals. The •SiCl3 radical then underwent sequential Cl losses to form :SiCl2, SiCl and Si. The C3H5 radical also underwent secondary reactions, producing a series of C3Hx species (m/z = 39–42), consistent with previous studies. In the pyrolysis of allyltrimethylsilane, molecular elimination reaction forming Me2Si=CH2 + C3H6 and Si–C bond ruptures producing Me3Si• + •C3H5 and Me2Si˙CH2CH=CH2 + •CH3 were identified as the main initiation decomposition steps. HSiMe3 was also identified as one of the initiation reaction products. The observed secondary reactions of Me2Si=CH2 and Me3Si• were consistent with previous studies. Possible thermal decomposition mechanism of the Me2Si˙CH2CH=CH2 product was also proposed.

Mechanistic Study of Thermal Decomposition of Hexamethyldisilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry and Density Functional Theory.

Thermal decomposition of hexamethyldisilane (HMDS) was studied from room temperature to 1310 K using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Decomposition pathways of HMDS and initial reaction intermediates were also investigated using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. Unimolecular decomposition reactions of HMDS involving Si-Si and Si-C bond cleavage, as well as decomposition producing Me4Si and :SiMe2 via a three-centered elimination, were determined as the initiation reactions. Me3SiSi(Me)2•, Me4Si, Me3Si•, and :SiMe2 were major products of the initiation reactions. These initial products were apt to decompose by homolytic reactions. Me2Si═CH2, :SiMe2, and other silene/silylene intermediates preferred decomposing through molecular eliminations. Both homolytic and molecular elimination reactions are important in the pyrolysis of HMDS.

Application of Vacuum Ultraviolet Single-photon Ionization Mass Spectrometer in Online Analysis of Volatile Organic Compounds

Abstract A vacuum ultraviolet single-photon ionization mass spectrometer, which has the merits of broad-spectrum soft ionization, low fragment peak, low matrix influence, high sensitivity and short response time, is fit for use in the online analysis of mixed volatile organic compounds. In this review, the theory and structural composition of the single-photon ionization mass spectrometer are described, and the current research progress of sampling systems, ionization sources, and mass spectrometers are summarized. Then, a summary is provided on how online analysis has been applied to the fields of atmospheric composition observation, atmospheric chemistry research, environmental monitoring, food detection, etc. Finally, the direction and trends for future work are proposed.

Methyl substitution effect in pyrolysis of coal-based model compound isomers

The thermal decomposition of three methyl anisole isomers (o-, m-, and p-methyl anisole) were investigated to understand the influences of methyl substitution position on the benzene ring at low pressure (below 15 Pa) within temperature range from 473 to 1473 K. The pyrolytic phenomena were studied by using vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) to identify the intermediates, radicals and final products, and the relative concentration profiles of the pyrolytic products were evaluated by the semiquantitative analysis method. It was showed that the bond homolysis of PhOCH3 was the initial reaction for all three methyl substituted anisole, and the produced intermediates and final products show similar among the pyrolysis experiments of three methyl anisole isomers. Moreover, the effects of the different substituted position on the benzene ring of the methyl group presented on the extraordinary differences of the maximum relative concentration of m/z 106 (6-methylen-2, 4-cyclohexadien-1-one or 4-methylene-2, 5-cyclohexadiene-1-one), The theoretical calculations indicate different generating pathways of m/z 106 for the pyrolysis of m-methyl anisole and o-, p-methyl anisole. Noteworthy, the isomerization reaction played a significant role in the pyrolysis of m-methyl anisole.

Flash Pyrolysis of t-Butyl Hydroperoxide and Di-t-butyl Peroxide: Evidence of Roaming in the Decomposition of Organic Hydroperoxides.

Thermal decomposition of t-butyl hydroperoxide and di-t-butyl peroxide was investigated using flash pyrolysis (in a short reaction time of <100 μs) and vacuum-ultraviolet (λ = 118.2 nm) single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS) at temperatures up to 1120 K and quantum computational methods. Acetone and methyl radical were detected as the predominant products in the initial decomposition of di-t-butyl peroxide via O-O bond fission. In the initial dissociation of t-butyl hydroperoxide, acetone, methyl radical, isobutylene, and isobutylene oxide products were identified. The novel detection of the unimolecular formation of isobutylene oxide, as supported by the computational study, was found to proceed via a roaming hydroxyl radical facilitated by a hydrogen-bonded intermediate. This new pathway could provide a new class of reactions to consider in the modeling of the low temperature oxidation of alkanes.

Emission of volatile organic compounds and production of secondary organic aerosol from stir-frying spices

Cooking is an important source of volatile organic compounds (VOCs) and a potential source of secondary organic aerosol (SOA) both indoors and outdoors. In this study, VOC emissions from heating corn oil and stir-frying spices (i.e. garlic, ginger, myrcia and zanthoxylum piperitum (Sichuan pepper)) were characterized using an on-line membrane inlet vacuum ultraviolet single-photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS). VOC emissions from heating corn oil were dominated by aldehydes, which were enhanced by factors of one order of magnitude when stir-frying spices. Stir-frying any of the spices studied generated large amounts of methylpyrrole (m/z 81). In addition, stir-frying garlic produced abundant dihydrohydroxymaltol (m/z 144) and diallyldisulfide (DADS) (m/z 146), while stir-frying ginger, myrcia and zanthoxylum piperitum produced abundant monoterpenes (m/z 136) and terpenoids (m/z 152, 154). SOA formed from emissions of stir-frying spices through reactions with excess ozone in a flow reactor as well as primary organic aerosol (POA) emissions were characterized using a scanning mobility particle sizer (SMPS) and a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS). Stir-frying garlic and ginger generated similar POA concentrations to those from heating corn oil while stir-frying myrcia and zanthoxylum piperitum generated double the amount of emissions. No SOA was observed from stir-frying garlic and ginger. The rates of SOA production from stir-frying myrcia and zanthoxylum piperitum were 1.8μgmin−1gspice−1 and 8.7μgmin−1gspice−1, equivalent to 13.4% and 53.1% of their own POA emission rates, respectively. Therefore, the contribution of stir-frying spices to ambient organic aerosol levels is likely dominated by POA. The rates of total terpene emission from stir-frying myrcia and zanthoxylum piperitum were estimated to be 5.1μgmin−1gspice−1 and 24.9μgmin−1gspice−1, respectively. Our results suggest that stir-frying spices could be an important source of terpenes in indoor environments in Hong Kong, at least during cooking.

Consumption and hydrocarbon growth processes in a 2-methyl-2-butene flame

This paper is concerned with the investigation of the chemical structure of a low-pressure, fuel-rich (ɸ = 1.8) premixed laminar flame fueled with 2-methyl-2-butene employing flame-sampling molecular-beam mass spectrometry with vacuum-ultraviolet single-photon ionization. Partially isomer-resolved mole fraction profiles can be explained by a decomposition scheme based on hydrogen abstraction and addition reactions. The presence of 9 allylic CH bonds compared to only one vinylic CH bond is the key feature that governs the fuel consumption and subsequent hydrocarbon growth reactions. Compared to other alkenes, including e.g., 1-butene, 2-butene, and iso-butene (Schenk et al., 2013), 2-methyl-2-butene shows a remarkable tendency to form soot precursor molecules such as toluene. In particular, experimental evidence is provided here that toluene, o-xylene, and styrene can be a starting point for PAH formation, thus serving as first aromatic rings besides benzene. The formation of toluene, o-xylene, and styrene can be traced back to the reactions of the resonantly stabilized C4H5 [∙CH2CCCH3 and CH2CH∙CCH2] radicals and the C5H7 [CH2C(CH3)∙CCH2] radicals that are readily formed through fuel-specific decomposition channels. Our experimental data in form of mole fraction profiles as a function of height above the burner for a mass range from 2 to 210 u can serve as reliable validation targets for model development. A preliminary comparison to the model of Westbrook et al. [1] that was optimized to capture ignition delay times and the low-temperature oxidation regime, shows promising elements already for the initial fuel consumption.

Unexpected methyl migrations of ethanol dimer under synchrotron VUV radiation.

While methyl transfer is well known to occur in the enzyme- and metal-catalyzed reactions, the methyl transfer in the metal-free organic molecules induced by the photon ionization has been less concerned. Herein, vacuum ultraviolet single photon ionization and dissociation of ethanol dimer are investigated with synchrotron radiation photoionization mass spectroscopy and theoretical methods. Besides the protonated clusters cation (C2H5OH)⋅H(+) (m/z = 47) and the β-carbon-carbon bond cleavage fragment CH2O⋅(C2H5OH)H(+) (m/z = 77), the measured mass spectra revealed that a new fragment (C2H5OH)⋅(CH3)(+) (m/z = 61) appeared at the photon energy of 12.1 and 15.0 eV, where the neutral dimer could be vertically ionized to higher ionic state. Thereafter, the generated carbonium ions are followed by a Wagner-Meerwein rearrangement and then dissociate to produce this new fragment, which is considered to generate after surmounting a few barriers including intra- and inter-molecular methyl migrations by the aid of theoretical calculations. The appearance energy of this new fragment is measured as 11.55 ± 0.05 eV by scanning photoionization efficiency curve. While the signal intensity of fragment m/z = 61 starts to increase, the fragments m/z = 47 and 77 tend to slowly incline around 11.55 eV photon energy. This suggests that the additional fragment channels other than (C2H5OH)⋅H(+) and CH2O⋅(C2H5OH)H(+) have also been opened, which consume some dimer cations. The present report provides a clear description of the photoionization and dissociation processes of the ethanol dimer in the range of the photon energy 12-15 eV.

Experimental and Theoretical Investigation on Three α,ω-Diarylalkane Pyrolysis

Pyrolysis of three α,ω-diarylalkane compounds (biphenyl, diphenylmethane, and bibenzyl) was performed below 30 Pa between 573 and 1473 K. Vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry was used to detect the reactants, radicals, and products. The relative concentration profiles of the pyrolysis species were estimated by a semi-quantitative analysis method. Experimental results indicated that the length of the C–C bridge bond plays an influential role in cracking of corresponding bonds in the α,ω-diarylalkane pyrolysis process. The C–H bond scission is dominant in pyrolysis of diphenylmethane at low temperatures, while the C–C bond scission competes with it when the temperature increases. The symmetrical homolysis of bibenzyl is a dominant reaction at low temperatures and will compete with the unsymmertrical cleavage reaction with increase of the temperature. In addition, the formation mechanism of fluorene, which plays a significant role in polycyclic aromatic hydrocarbon generation, during diphenylmethane pyrolysis was discussed by combining the experimental observation with the theoretical calculation. The theoretical calculation supported these experimental results at the mPW2PLYP level.

Thermal decomposition of tetramethylsilane and tetramethylgermane by flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry

Thermal decomposition of tetramethylsilane (TMS) and tetramethylgermane (TMG) was studied on a short time scale of 20–100μs using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Primary decomposition of TMS and TMG occurred via loss of a methyl radical to form Si(CH3)3 and Ge(CH3)3, respectively. Both the Si(CH3)3 and Ge(CH3)3 radicals underwent secondary loss of a second methyl radical to form :Si(CH3)2 and :Ge(CH3)2, respectively. A previously unobserved secondary decomposition process in TMS involving loss of H atom from Si(CH3)3 followed by elimination of H2 to form SiC3H8, SiC3H6, and SiC3H4 was also identified. Sequential loss of the third and fourth methyl radical with significant formation of Ge and Ge2 was observed in the TMG pyrolysis. Loss of a third methyl radical in the TMS pyrolysis was not significant, while Si and SiC products were possibly produced. Secondary reactions of methyl to form unsaturated CxHy species, particularly in the TMG decomposition, were also observed.

Determination of Dimethyl Sulfide in Gas Samples by Single Photon Ionization Time of Flight Mass Spectrometry

It is difficult to determine sulfur-containing volatile organic compounds in the atmosphere because of their reactivity. Primary off-line techniques may suffer losses of analytes during the transportation from field to laboratory and sample preparation. In this study, a novel method was developed to directly measure dimethyl sulfide at parts-per-billion concentration levels in the atmosphere using vacuum ultraviolet single photon ionization time-of-flight mass spectrometry. This technique offers continuous sampling at a response rate of one measurement per second, or cumulative measurements over longer time periods. Laboratory prepared samples of different concentrations of dimethyl sulfide in pure nitrogen gas were analyzed at several sampling frequencies. Good precision was achieved using sampling periods of at least 60 seconds with a relative standard deviation of less than 25%. The detection limit for dimethyl sulfide was below the 3 ppb olfactory threshold. These results demonstrate that single photon ionization time-of-flight mass spectrometry is a valuable tool for rapid, real-time measurements of sulfur-containing organic compounds in the air.

Vacuum Ultraviolet Photon Ionization Mass Spectrometer for Detection of Dioxin Precursors

Waste incineration has been considered as a main source of dioxins. During the generation of dioxins, dioxin precursors, such as polychlorinated benzenes ( PCBz), polychlorinated phenols ( PCPh), polycyclic aromatic hydrocarbon ( PAHs), polychlorinated biphenyls ( PCBs) etc., have been proved to be produced with much higher concentrations than dioxins, which had been determined to be closely related to dioxin toxic equivalents. Therefore, online monitoring of these precursor compounds has been becoming one of the main research directions of dioxin detection. In this paper, we reported our attempt on developing a new method for online detection of these dioxin precursors in gas phase, by nanosecond vacuum ultraviolet single photon ionization technique, combined with time. of. flight mass spectrometer. This setup was evaluated by monitoring chlorobenzene, polychlorinated phenols and naphthalene in gas phase. In the range of 5-100 mu g/L, parent ion signal intensity of chlorobenzene exhibits linear dependence on the concentration.