Scheme for collinear ionization in supersonic jet/multiphoton ionization/time-of-flight mass spectrometry

Onoda, Takayuki; Saito, Genta; Imasaka, Totaro

doi:10.1016/s0003-2670(00)00757-1

Cited by 28 publications

(23 citation statements)

References 7 publications

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“…The jet-expansion is sampled anywhere between 15-25 mm downstream of the pulsed valve, just behind the sudden-freeze surface of the jet expansion, where the molecule density is still relatively high. Further reduction in the distance to ionization has been documented by Onoda et al [12]. In this arrangement, the jet is expanded collinear with the axis of ion flight, shown in Figure 1c.…”

supporting

confidence: 56%

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Development of medium pressure laser ionization, MPLI. Description of the MPLI ion source

Appel

Short

Benter

2004

J. Am. Soc. Mass Spectrom.

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A novel pulsed valve/ion source combination capable of time-resolved sampling from atmospheric pressure has been developed for use with laser ionization time of flight mass spectrometry. The source allows ionization extremely close to the nozzle of the pulsed valve, enabling ultra-sensitive detection of a number of compounds, e.g., NO, at mixing ratios Ͻ1 pptV. Furthermore, at analyte mixing ratios in the ppbV range, the temporal resolution of the system is in the sub-second regime, allowing time-resolved monitoring of highly dynamic and complex mixtures, e.g., human breath or reacting chemical mixtures in atmospheric smog chamber experiments. Rotational temperatures of ϳ50 K have been observed for analytes seeded in the supersonic jet expansion at a distance of 1 mm downstream of the nozzle orifice. The refinement of the original ion source has drastically reduced the impact of reflected laser light and the resultant electron impact signals previously observed. The general applicability of this technique is demonstrated here by coupling the source to commercially available as well as home-built time-of-flight mass spectrometers. Finally, we discuss the MPLI technique in view of the very recently introduced atmospheric pressure laser ionization (APLI) as well as the traditional jet

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supporting

confidence: 56%

“…The unskimmed jet is ionized roughly 2.5 cm downstream of the nozzle orifice. (c) Collinear ionization scheme as reported by Onoda et al [12]. This method uses a line beam focus configuration for increased ionization volume, which is located roughly 1 cm downstream of the unskimmed jet.…”

Section: Laser Systemsmentioning

confidence: 99%

Development of medium pressure laser ionization, MPLI. Description of the MPLI ion source

Appel

Short

Benter

2004

J. Am. Soc. Mass Spectrom.

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“…The technique described herein is essentially based on proximity ionization, which is a technique for ionizing an analyte behind the nozzle for expansion of the molecule into a vacuum. 10 This approach increases the density of the analyte molecule in the ionization region, thereby improving the ionization efficiency. A variety of electrode assemblies were made and evaluated for optimizing the ion trajectory using the SIMION software.…”

Section: Introductionmentioning

confidence: 99%

“…The basic principle has been reported elsewhere, and is only briefly described here. 10 The sample gas at a specified concentration is generated using a standard gas generator (Gastec, Permeater). The sample gas is introduced from a pulsed nozzle into a vacuum for mass spectrometry.…”

Section: Introductionmentioning

confidence: 99%

Use of Ring-Repeller, Double-Skimmer Electrodes for Efficient Ion Focusing in Mass Spectrometry

2002

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The design and construction of a new type of time-of-flight mass spectrometer is described. The instrument was designed to improve the ionization efficiency and to efficiently detect ions. The system performance was evaluated using the SIMION software, and was compared with the experimental results. The shapes of the repeller, extraction, and ground electrodes had a strong effect on the trajectory of ions in the processes of ion acceleration and focusing. The major difference between the theory and the experiment can be attributed to space-charge effects.

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“…The principles of operation of SSJ/REMPI/TOF-MS and SRS have been described previously. [11][12][13] The second-harmonic emission of an optical parametric oscillator (Spectra-Physics, MOPO-730, 1 mJ, 6 ns, 0.2 cm -1 ) is focused by a lens into a Raman cell filled with hydrogen. The two-color beam generated by SRS is focused into a jet.…”

mentioning

confidence: 99%

Resonance-enhanced Multiphoton Ionization Mass Spectrometry Using a Two-color Laser Beam Generated by Stimulated Raman Scattering

2003

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A wide variety of chemical species, such as chlorinated aromatic hydrocarbons, are emitted from an incinerator. Among such compounds, polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/F) are known to be extremely toxic, and the on-line real-time monitoring of such compounds would be highly desirable. A lengthy pretreatment process followed by high-resolution gas chromatography/mass spectrometry is the current method of choice for the analysis of PCDD/F. 1,2 However, this type of approach is not suitable for the on-line real-time monitoring of PCDD/F emitted from an incinerator.Resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (REMPI/TOF-MS) 3,4 constitutes an attractive solution to this problem. Combined with supersonic jet spectrometry (SSJ), 5,6 REMPI/TOF-MS provides superior selectivity than the conventional (room temperature) approach, as the result of sharp spectral features obtained by jet expansion and subsequent molecular cooling. However, there are several problems associated with the measurements of PCDD/F by SSJ/REMPI/TOF-MS. In particular, the ionization potential increases and the 0-0 transition energy decreases with increasing numbers of substituted chlorine atoms, as reported for PCDD. Therefore, the energy of the photon used for excitation at the 0-0 transition becomes insufficient for use in subsequent ionization from the excited state to the ionized levels. For this reason, it is necessary to use a three-photon process, but the efficiency is rather poor. In addition, a highpower laser is needed for three-photon ionization, which leads to non resonant ionization, and makes differentiation of the isomers of PCDD/F difficult. In order to solve this problem, two-color REMPI has been developed. [7][8][9][10] In two-color REMPI, the first photon, with an energy less than the second one, is used for excitation, and the second photon (higher energy than the first) is used for ionization of the molecule, for example, in the case of PCDD/F. A laser source consisting of two sets of laser systems emitting at different wavelengths is currently used for this purpose, although the ionization laser (e.g., the fourth harmonic emission of the Nd:YAG laser) is sometimes constructed utilizing the same Nd:YAG laser as that employed for pumping the tunable laser to simplify the system. 7-10 This approach is complicated because two laser beams (pulses) must be both spatially and temporally adjusted to each other. Moreover, the analytical system becomes more expensive because two lasers are needed. As a result, it is impractical for use in applications to the on-line monitoring of PCDD/F emitted from an incinerator.In this study, SSJ/REMPI/TOF-MS using a two-color laser system was demonstrated. In this technique, a single-color (fundamental) laser beam is focused into molecular hydrogen to generate a Stokes beam by stimulated Raman scattering (SRS). 11 The two beams (pulses) are spatially and temporally superimposed, and can be readily used as a two-color beam for REMPI u...

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Scheme for collinear ionization in supersonic jet/multiphoton ionization/time-of-flight mass spectrometry

Cited by 28 publications

References 7 publications

Development of medium pressure laser ionization, MPLI. Description of the MPLI ion source

Development of medium pressure laser ionization, MPLI. Description of the MPLI ion source

Use of Ring-Repeller, Double-Skimmer Electrodes for Efficient Ion Focusing in Mass Spectrometry

Resonance-enhanced Multiphoton Ionization Mass Spectrometry Using a Two-color Laser Beam Generated by Stimulated Raman Scattering

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