Laser‐induced electron impact ionization in a reflectron time‐of‐flight mass spectrometer

Moritz, Friedrich; Dey, Michael; Zipperer, K.; Prinke, S.; Grotemeyer, Jürgen

doi:10.1002/oms.1210281218

Cited by 14 publications

(7 citation statements)

References 25 publications

(2 reference statements)

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“…Classical EI-type mass spectra are observed. Further study indicated that the photoelectrons generated by the laser−metal interaction are responsible for the ionization process in these experiments, in line with other studies using the photoelectric effect to induce electron impact ionization. − It was demonstrated that this ionization technique can provide relatively uniform ionization efficiencies for both aromatic and nonaromatic compounds. The ionization efficiency can be quite high.…”

supporting

confidence: 84%

Surface Analysis of Bulk Polymers Using Laser-Induced Photoelectron Ionization with Laser Desorption in a Time-of-Flight Mass Spectrometer

Schriemer

1996

Anal. Chem.

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Laser desorption combined with photoelectron ionization in a time-of-flight mass spectrometer has been developed for surface analysis of bulk polymers. In this technique, a CO 2 laser beam is focused onto a polymer surface to induce fast thermal dissociation and/or photodissociation of the polymeric materials. The resulting neutral species are then ionized using photoelectron ionization (PEI). The PEI process involves a laser-metal interaction in which a low-power, pulsed UV laser beam is directed to an appropriate metal surface exterior to the source region of a Wiley-McLaren time-of-flight mass spectrometer. The photoelectrons generated are accelerated as a narrowly distributed beam by the fringing fields of the source region. The electron beam, traveling in a direction almost parallel to the extraction grid, is used to ionize the desorbed neutrals that are entrained into the ionization region. A number of polymers of different molecular weight and monomer structure are examined using this technique. It is found that this technique can produce readily interpretable mass spectra for structural analysis and chemical identification. The application of this technique for terminal group analysis in chemically modified polymers is illustrated. A comparison of this technique with other mass spectrometric methods is presented. In addition, it is shown that the detection sensitivity can be very high, with a detection limit of <100 amol per laser shot for poly(ethylene glycol).Mass spectrometry plays an important role in polymer analysis. Both direct pyrolysis/mass spectrometry and pyrolysis/gas chromatography/mass spectrometry are used extensively in the analysis of bulk polymers. 1,2 Desorption ionization mass spectrometric techniques, such as secondary ion mass spectrometry (SIMS) and laser desorption ionization mass spectrometry (LDMS), are used for polymer surface characterization with high sensitivity and specificity. 3 A common feature of these desorption techniques is that the desorption process and the ionization process are combined in one step. Since the ion generation is strongly dependent on the chemical composition and the chemical environment of the polymer surface, spectral interpretation and quantitation can sometimes become rather difficult. It is also known that, in desorption ionization techniques, the majority of the

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supporting

confidence: 84%

Surface Analysis of Bulk Polymers Using Laser-Induced Photoelectron Ionization with Laser Desorption in a Time-of-Flight Mass Spectrometer

Schriemer

1996

Anal. Chem.

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“…Mass spectrometry of vibrationally cold molecules in free jet or SMB was also explored by Nir et al 26 and Moritz et al 27 While we used a quadrupole as the mass analyzer for GC‐MS with SMB, the same as that of Kishi and Fujii28–31 who used it with hyperthermal surface ionization (HSI), time of flight was used by Heger et al ,32 Hafner et al 33 and Mitschke et al 34 with laser ionization, with and without GC separation, and by Davis et al 35, 36 with EI and HSI.…”

Section: Introductionmentioning

confidence: 99%

Gas chromatography‐mass spectrometry with supersonic molecular beams

et al. 2008

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Gas chromatography-mass spectrometry (GC-MS) with supersonic molecular beams (SMBs) (also named Supersonic GC-MS) is based on GC and MS interface with SMBs and on the electron ionization (EI) of vibrationally cold analytes in the SMBs (cold EI) in a fly-through ion source. This ion source is inherently inert and further characterized by fast response and vacuum background filtration capability. The same ion source offers three modes of ionization including cold EI, classical EI and cluster chemical ionization (CI). Cold EI, as a main mode, provides enhanced molecular ions combined with an effective library sample identification, which is supplemented and complemented by a powerful isotope abundance analysis method and software. The range of low-volatility and thermally labile compounds amenable for analysis is significantly increased owing to the use of the contact-free, fly-through ion source and the ability to lower sample elution temperatures through the use of high column carrier gas flow rates. Effective, fast GC-MS is enabled particularly owing to the possible use of high column flow rates and improved system selectivity in view of the enhancement of the molecular ion. This fast GC-MS with SMB can be further improved via the added selectivity of MS-MS, which by itself benefits from the enhancement of the molecular ion, the most suitable parent ion for MS-MS. Supersonic GC-MS is characterized by low limits of detection (LOD), and its sensitivity is superior to that of standard GC-MS, particularly for samples that are hard for analysis. The GC separation of the Supersonic GC-MS can be improved with pulsed flow modulation (PFM) GC x GC-MS. Electron ionization LC-MS with SMB can also be combined with the Supersonic GC-MS, with fast and easy switching between these two modes of operation.

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“…28,29 When using the laser light of medium power densities (10 6 to 10 9 W cm À2 ), thermionic electron emission due to heating of the metal by photon absorption dominates. 15 In this work, the effect of the laser power density on the signal strength of Ar + using the 25% Ar/He sample was studied in order to understand the mechanism of electron emission at work in our system. The 355 nm laser radiation was focused 5 mm in front of the stainless steel rod.…”

Section: Ionization Mechanismmentioning

confidence: 99%

“…Production of pulsed electron beams for efficient ionization from laser-metal interactions has also been widely explored. In the earlier work [13][14][15] , a tantalum (Ta) wire was placed in between the repeller plate and the extraction grid of an existing TOF MS. Photoelectrons were produced when a laser beam of photon energy higher than the work function of Ta hit the wire. Pulsed electron beams can also be produced by directing the laser beam to the extraction grid, 16 the repeller plate 17,18 or a stainless steel target 19 outside the ion optics of a TOF MS.…”

Section: Introductionmentioning

confidence: 99%

Development of a new laser induced electron impact ionization source for studying the hot-wire chemical vapor deposition chemistry of silane–ammonia mixtures

Eustergerling

Hedén

Shi

2008

J. Anal. At. Spectrom.

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A newly-developed laser induced electron impact ionization (LIEI) method is presented. In this method, electrons are generated by thermionic emission when directing a low-power, pulsed UV laser beam to a stainless steel rod exterior to the ion optics of a time-of-flight mass spectrometer. The electrons are collimated into a beam almost parallel to the ion optics by the electric field between the rod and a copper mesh placed in the vicinity and the utilization of a delayed ion extraction pulse. It has been demonstrated that EI-type mass spectra can be obtained with a mass resolution that is comparable to that using laser ionization. The detection sensitivity is very high, with a detection limit of < 32 attomole for NH 3 . The gas-phase chemistry of SiH 4 /NH 3 mixtures in the hot-wire chemical vapor deposition (HWCVD) process was examined using the new LIEI source. It is found that this method is well suited for detecting stable species with high ionization potentials, such as H 2 and N 2 , which characterizes the NH 3 decomposition chemistry in a HWCVD reactor. The suppression of NH 3 chemistry by the presence of SiH 4 in the mixture is demonstrated, as is the temperature dependence of the suppression extent.

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Laser‐induced electron impact ionization in a reflectron time‐of‐flight mass spectrometer

Cited by 14 publications

References 25 publications

Surface Analysis of Bulk Polymers Using Laser-Induced Photoelectron Ionization with Laser Desorption in a Time-of-Flight Mass Spectrometer

Surface Analysis of Bulk Polymers Using Laser-Induced Photoelectron Ionization with Laser Desorption in a Time-of-Flight Mass Spectrometer

Gas chromatography‐mass spectrometry with supersonic molecular beams

Development of a new laser induced electron impact ionization source for studying the hot-wire chemical vapor deposition chemistry of silane–ammonia mixtures

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