Single Photon Ionization Mass Spectrometry Research Articles

Laser Desorption Single-Photon Ionization of Asphaltenes: Mass Range, Compound Sensitivity, and Matrix Effects

Molecular-level characterization of petroleum asphaltenes is important for addressing reservoir concerns such as connectivity and flow assurance. Laser desorption single-photon ionization mass spectrometry (LDSPI-MS) has emerged as a favored technique for asphaltene analysis, because of its ability to detect these samples with minimal artifacts from fragmentation, aggregation, and multiple charging. However, questions persist regarding the sensitivity of LDSPI-MS to different components of asphaltenes, the molecular weight range detectable with the technique, and the importance of matrix effects. We present LDSPI-MS mass spectra of mixtures of model compounds and asphaltenes in various matrices to assess the significance of these effects. We observe that LDSPI-MS has comparable sensitivity for all studied model compounds and for asphaltenes, including compounds with molecular weight exceeding 1500 Da. In addition, only a minimal matrix effect is observed, as expected from considerations of the desorption ...

Coupling of stir bar sorptive extraction with single photon ionization mass spectrometry for determination of volatile organic compounds in water

A home-made stir bar sorptive extraction (SBSE) apparatus was combined to a single photon ionization time-of-flight mass spectrometer (SPI-TOFMS) for rapid and sensitive determination of trace volatile organic compounds (VOCs) in water. The home-made SBSE bar, low-cost and disposable, was used for VOCs extraction. A thermal desorption (TD) device was designed to desorb the analytes from the SBSE bar, and a high throughput interface was developed to transfer the analytes into the ionization chamber of the SPI-TOFMS. The combination of large extraction volume of SBSE bar, and the direct measurement power of SPI-TOFMS enable a short analysis time for VOCs in water with high sensitivity, for example the limits of detection (LODs) were in the range of 7.4-11.1 ng L(-1) for benzene, toluene, and p-xylene (BTX) within 15 min. BTX aqueous solutions were chosen to demonstrate the quantitative capability, the linear range was from 0.05 to 100 μg L(-1) and the correlation coefficients were better than 0.996. The proposed method was successfully applied for the analysis of VOCs in urban river water.

Real-time Detection of 1-Nitronaphthalene in Atmosphere by Single-photon Ionization Mass Spectrometry

自動車排ガスからの発生が懸念されているニトロ多環芳香族炭化水素（NPAHs）は，発癌性が高いことが知られている．NPAHsの代表分子である1－ニトロナフタレンは，通常のガス分析時には分子開裂を起こしやすいため，定量分析が困難であった．本研究では，NPAHsの発生をリアルタイムにモニタリングするため，超音速ジェット光イオン化質量分析法に着目し，その可能性を検証した．測定には，各種レーザー光を用いて，共鳴多光子イオン化過程（REMPI, resonance enhanced multi-photon ionization），非共鳴多光子イオン化過程（NRMPI, non-resonance multi-photon ionization），真空紫外1光子イオン化過程（VUV-SPI, vacuum-ultraviolet single photon ionization）を比較し，1－ニトロナフタレンの定量測定とリアルタイムモニタリングに対する有効性を検討した．その結果，VUV-SPI法のみが分子開裂が無く定量的に測定でき，上記目的に最も適していることを明らかにした．本研究で開発したVUV-SPI装置の検出時間分解能は30秒であった．

Online Comprehensive Two-Dimensional Characterization of Puff-by-Puff Resolved Cigarette Smoke by Hyphenation of Fast Gas Chromatography to Single-Photon Ionization Time-of-Flight Mass Spectrometry: Quantification of Hazardous Volatile Organic Compounds

This work presents the direct coupling of a custom-made smoking machine (SM) to fast gas chromatography combined with single-photon ionization mass spectrometry (GC × SPI-MS) utilizing a six-port, two-position valve for online puff-resolved comprehensive two-dimensional investigation of cigarette smoke. The innovative electron-beam pumped rare gas excimer light source (EBEL) filled with argon provided vacuum ultraviolet (VUV) photons of 9.8 ± 0.4 eV (126 ± 9 nm) for SPI. Puff-by-puff quantification of 14 hazardous volatile organic smoke constituents from the 2R4F Kentucky research cigarette was enabled for two smoking regimes, i.e., ISO and Canadian Intense, after determination of photoionization cross sections. The investigated analytes comprised NO, acetaldehyde, butadiene, acrolein, propanal, acetone, isoprene, furan, crotonaldehyde, isobutanal, butanal, 2-butanone, benzene, and toluene. The determined amounts of these compounds in cigarette smoke agreed excellently with the literature values. Furthermore, the two well-known patterns of puff-by-puff behaviors for these different smoke constituents were obtained for both whole smoke and gas-phase measurements.

Determination of Photoionization Cross-Sections of Different Organic Molecules Using Gas Chromatography Coupled to Single-Photon Ionization (SPI) Time-of-Flight Mass Spectrometry (TOF-MS) with an Electron-Beam-Pumped Rare Gas Excimer Light Source (EBEL): Influence of Molecular Structure and Analytical Implications

This work describes a fast and reliable method for determination of photoionization cross-sections (PICS) by means of gas chromatography (GC) coupled to single-photon ionization mass spectrometry (SPI-MS). Photoionization efficiency (PIE) data for 69 substances was obtained at a photon energy of 9.8 ± 0.4 eV using an innovative electron-beam-pumped rare gas excimer light source (EBEL) filled with argon. The investigated analytes comprise 12 alkylbenzenes as well as 11 other substituted benzenes, 23 n-alkanes, ten polyaromatic hydrocarbons, seven aromatic heterocycles, and six polyaromatic heterocycles. Absolute PICS for each substance at 9.8 eV are calculated from the relative photoionization efficiencies of the compounds with respect to benzene, whose photoionization cross-section data is well known. Furthermore, a direct correlation between the type of benzene substituents and their absolute PICS is presented and discussed in depth. Finally, comparison of previously measured photoionization cross-sections for 20 substances shows good agreement with the data of the present work.

Highly Resolved Online Organic-Chemical Speciation of Evolved Gases from Thermal Analysis Devices by Cryogenically Modulated Fast Gas Chromatography Coupled to Single Photon Ionization Mass Spectrometry

Multi-dimensional analysis (MDA) in analytical chemistry is often applied to improve the selectivity of an analytical device and, therefore, to achieve a better overview of a sample composition. Recently, the hyphenation of thermogravimetry with single photo ionization mass spectrometry (TG-SPIMS) using an electron beam pumped excimer lamp (EBEL) for VUV radiation was applied. The concept of MDA has been realized by upgrading the TG-SPIMS system with a quasi comprehensive chromatographic separation step before the soft ionization (TG-GCxSPIMS). The system was characterized by the thermal analysis of diesel fuel, which has often been investigated by the GCxGC-community and is therefore a well-known sample material in MDA. Data from this measurement are used to explain the three-dimensional data structure and the advantages of the online TG-GCxSPIMS as compared to TG-SPIMS. Subsequently, the thermal decomposition behavior of a polymer, acrylonitrile-butadiene-styrene (ABS), is investigated. TG-GCxSPIMS provides a two-dimensional analysis of the evolved gaseous products. TG relevant data are obtained as well as an improved resolution power to separate isobaric molecular structures without losing any fraction of the samples, as is often the case in heart cutting approaches. Additionally, this solution is not associated with any extension of the measurement time. The assignment of the substance pattern to distinct species is improved as compared to solely using mass spectrometry without a preceding separation step. Furthermore, hitherto undetected compounds have been found in the evolved gases from the thermal degradation of ABS. Finally, a first estimation of the limit of detection has been carried out. This results in a significant decrease of the LOD in case of TG-GCxSPIMS (500 ppt for toluene) as compared to 30 ppb, which could be reached with TG-SPIMS.

Electronic Structure and Spectroscopy of Nucleic Acid Bases: Ionization Energies, Ionization-Induced Structural Changes, and Photoelectron Spectra

We report high-level ab initio calculations and single-photon ionization mass spectrometry study of ionization of adenine (A), thymine (T), cytosine (C), and guanine (G). For thymine and adenine, only the lowest-energy tautomers were considered, whereas for cytosine and guanine we characterized the five lowest-energy tautomeric forms. The first adiabatic and several vertical ionization energies were computed using the equation-of-motion coupled-cluster method for ionization potentials with single and double substitutions. Equilibrium structures of the cationic ground states were characterized by DFT with the ωB97X-D functional. The ionization-induced geometry changes of the bases are consistent with the shapes of the corresponding molecular orbitals. For the lowest-energy tautomers, the magnitude of the structural relaxation decreases in the following series, G > C > A > T, the respective relaxation energies being 0.41, 0.32, 0.25, and 0.20 eV. The computed adiabatic ionization energies (8.13, 8.89, 8.51-8.67, and 7.75-7.87 eV for A, T, C, and G, respectively) agree well with the onsets of the photoionization efficiency (PIE) curves (8.20 ± 0.05, 8.95 ± 0.05, 8.60 ± 0.05, and 7.75 ± 0.05 eV). Vibrational progressions for the S(0)-D(0) vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra and differentiated PIE curves.

Chemical redox recovery of giant, small-gap and other fullerenes

A simple method for extracting otherwise insoluble fullerenes into organic solvents is presented. The fullerenes are reduced to anionic charge states by contact with zinc in the presence of an alkylphosphonium salt in tetrahydrofuran. The anionic fullerenes become soluble, and the non-fullerene carbon matrix is separated by filtration. The anionic fullerenes can then be precipitated from solution by the action of a chemical oxidant such as iodine. It is also shown that there are approximately as many fullerenes left behind in carbon arc soot after solvent extraction as are extracted by the solvent. In contrast, more than twice as many fullerenes are left behind in combustion-produced fullerene soot as are solvent-extracted. Thus, approximately 70% of the total recovered carbon product from large-scale combustion synthesis is fullerenes. Conversely, no detectable amount of fullerenes can be recovered from conventional carbon blacks under the same conditions. Analysis by single photon ionization mass spectrometry suggests that C 60 and C 70 account for almost half of the fullerenes that were not solvent-extractable, suggesting that they are readily incorporated into toluene-insoluble fullerene polymers. The redox process presented here is easily up-scaled, and we routinely recover 100 g of heretofore insoluble fullerenes in 8 h.

Probing low-energy electron induced DNA damage using single photon ionization mass spectrometry

Single photon ionization mass spectrometry (SPI MS) followed by gel electrophoresis was developed for investigation of low-energy electron (LEE) induced DNA damage. This method detects neutral species generated from DNA molecules during LEE irradiation. The neutral yields are then correlated with single strand breaks (SSBs) and double strand breaks (DSBs) as a function of incident electron energy. Specifically, fragments with masses of m/z=27, 68 and 69 show resonance structure between 6–12 and 15–25eV which is similar to that observed in the SSB and DSB probabilities. These fragments are likely associated with sugar damage and dissociative electron attachment (DEA) channels. Other fragments with masses of m/z=45, 56, 67 and 70 show a monotonic increase at threshold energies around 10–12eV, indicating the possible role of direct dissociative excitation or ionization. Resonance structure above the 10–12eV threshold for fragments with masses of m/z=43, 44, 67 and 70 are also observed and can be associated with compound states in the continuum and core-excited excitations. The results support the contention that DEA resonances localized on DNA sub-units can lead to damage, especially at energies below the ionization threshold. Damage also occurs due to direct dissociative excitation and dissociative ionization.

The tunable VUV single-photon ionization mass spectrometry for the analysis of individual components in gasoline

A procedure combining tunable vacuum ultraviolet (VUV) single-photon ionization with reflectron time-of-flight mass spectrometer has been developed for analysis of individual components in 90# unblended gasoline. Synchrotron radiation used as the ionization source can provide wide energy range and high resolution. All components can be identified by the molecular weights from photoionization mass spectrometry near threshold ionization and the ionization energies from photoionization efficiency spectra. About ninety components are detected in this study, including paraffins, olefins, and aromatics. Quantitative analysis can be obtained by the integrated ion intensity combining with data of photoionization cross-section. It appears that the tunable VUV photoionization mass spectrometry is a complementary method to previous existing ones for the analysis of individual components in gasoline. It may also be useful in other analytical applications.

Analysis of Organoselenium and Organic Acid Metabolites by Laser Desorption Single Photon Ionization Mass Spectrometry

A method for analyzing organoselenium and organic acid metabolites using laser desorption from graphite surfaces coupled to vacuum ultraviolet single photon ionization mass spectrometry (LD/SPI MS) is described. The 1-10-fmol sensitivity and linear dynamic range allows quantitative detection of selenomethionine, trimethylselenonium ion, methylselenogalactosamine, and 1beta-methylseleno-N-acetyl-D-galactosamine in complex biological samples such as human urine. In addition, common urinary metabolites such as tartronic, glutaric, orotic, uric, suberic, and hydroxyhippuric acids, are readily detected. Screening and quantitative detection of these organoselenium and organic acid metabolites is achieved within minutes. The results are also consistent with those obtained using high-performance liquid chromatography tandem mass spectrometry techniques. The study demonstrates the viability of matrix-free LD/SPI MS for molecular characterization and quantitative analysis of biological metabolites in the m/z 10-500 range that are present in complex biological fluids.

SINGLE-PHOTON IONIZATION OF THE PRIMARY PHOTOFRAGMENTS OF CHLORINE MONOXIDE

The single-photon ionization mass spectrometry of primary photofragments of chlorine monoxide (ClO) is reported. The use of laser-produced plasma (LPP) radiation in pump–probe experiments allows us to ionize the laser-generated atomic photoproducts with tunable radiation in the vacuum ultraviolet regime (E = 10–18 eV). Autoionization resonances of the atomic photoproducts are used to establish the quantum states of the photoproducts and to enhance the detection sensitivity. Predissociation and direct dissociation of A (2Π)-excited ClO yields Cl (2 P )+ O (3 P ) as well as Cl (2 P )+ O (1 D ), respectively. The quantum yield of O (1 D ) formation is reported in the threshold regime near the ClO [ A (2Π)] dissociation limit.

Laser single-photon ionization mass spectrometry measurements of SiCl and SiCl2 during thermal etching of Si(100)

Pulsed laser single-photon ionization time-of-flight mass spectrometry is used to investigate the etch products resulting from thermal etching of Si(100) with molecular chlorine over a temperature range of 1023–1373 K and a pressure range of 10−5–10−4 Pa. In this regime, two thermal etch products, SiCl2 and SiCl, are directly observed by ionization without fragmentation using 118 nm light. Over this temperature and pressure range, the desorption fluxes of SiCl2 and SiCl are proportional to the dosing chlorine pressure. A phenomenological activation energy of 0.36±0.03 eV is observed for the SiCl desorption flux from an Arrhenius plot. The SiCl2 product flux exhibits a complex temperature dependence, first increasing and then decreasing, and thus this rate is controlled by at least two pathways. One pathway in the lower temperature regime may be a direct desorption channel. The other process at higher temperatures may be a competing reaction that limits the precursor species, most likely SiCl, for the formation of SiCl2 on the surface. The ability to detect the radical species without mass spectral cracking provides the potential to unravel such complex pathways.

Laser single photon ionization mass spectrometry of linear, branched and cyclic hexanes

VUV light of 118.2 nm (10.49 eV) is produced by frequency tripling the third harmonic of a Nd: YAG laser (354.6 nm) in a Xe cell. With these photons time-of-flight mass spectra of n-hexane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane and cyclohexane are obtained by single photon ionization. The simple set-up for production of 118.2 nm photons, the necessity of separating the 354.6 nm photons and the obtained mass spectra are discussed. The fragmentation of hexane as a function of its temperature is compared with the predictions from quasi-equilibrium theory. The model shows that for n-hexane less than 50% of the difference between photon energy and ionization energy is deposited in the molecular ion.