Electron monochromator-mass spectrometer instrument for negative ion analysis of electronegative compounds

Laramee, J. A.; Mazurkiewicz, Paul; Berkout, Vadym D.; Deinzer, Max L.

doi:10.1002/(sici)1098-2787(1996)15:1<15::aid-mas2>3.0.co;2-e

Cited by 44 publications

(46 citation statements)

References 69 publications

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“…Therefore, a 1 mJ pulsed laser, with a 10 ns pulse duration, operating at 290 nm and 10 Hz will yield a continuous current of about 200 nA. This is comparable to current values reported for electron monochromators, ranging from 0.5-2 A [9]. However, due to the pulsed nature of the PERCI source, its sensitivity is enhanced since the instantaneously high electron current is more effectively coupled to the pulsed ion collection of the TOF-MS.…”

Section: Demonstration Of Percisupporting

confidence: 71%

mentioning

confidence: 99%

“…Two instruments capable of REC ionization, suited for gas phase studies, are the throchoidal electron monochromator [9] and the reversal electron attachment detector (READ) [10]. The electron monochromator uses crossed electric and magnetic fields to force different trajectories on electrons with different energies.…”

mentioning

confidence: 99%

“…An offset exit aperture allows monoenergetic electrons to pass into the source region of a mass spectrometer. A more detailed discussion can be found in the reference by Laramee et al [9]. READ operates by reversing the direction of a focused electron beam; at the point of reversal, the kinetic energy of the electrons theoretically becomes zero.…”

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confidence: 99%

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Photoelectron resonance capture ionization (PERCI): A novel technique for the soft-ionization of organic compounds

LaFranchi

Petrucci

2004

J. Am. Soc. Mass Spectrom.

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Photoelectron resonance capture ionization (PERCI) is demonstrated as a sensitive ionization technique involving minimal fragmentation of organic molecules. PERCI has been used successfully to softly and efficiently ionize both strongly UV absorbing and non-absorbing molecules. Tunable low energy (Ͻ1 eV) electrons are generated by focusing a pulsed UV laser on an aluminum photocathode in the presence of gas phase analyte. Negative ions are formed through a resonance electron capture process. Mass analysis is done using a reflectron time-of-flight mass spectrometer. PERCI is demonstrated for a number of gas phase compounds and simple mixtures, including sulfur hexafluoride, nitrobenzene, nitrophenol, 2-pentanone, hexanal, heptanal, and octanal. In all cases the molecular ion (or [M Ϫ H] Ϫ ) was observed to be the dominant peak. The 1 limit of detection was estimated to be on the order of 10 6 molecules in the ionization region. . It has been shown that the result of low energy electron attachment depends heavily upon the electron energy [1]. For instance, at a particular electron energy ( ), associative attachment can occur leaving the molecular anion radical present. At a different , dissociative electron attachment can occur in which the molecule breaks apart to give a neutral radical species and a fragment anion. The favored pathway is also a function of the structural and electronic properties of the molecule. The electron capture phenomenon, known as resonance electron capture (REC), has proved to be a very useful ionization method for the detection of a variety of classes of organic compounds by mass spectrometry. It has been shown to efficiently ionize organic molecules functionalized with halogens, nitrates, sulfur, conjugated -systems and carbonyls [2][3][4][5], as well as straight-chain hydrocarbons with minimal functionality [6]. Most recently, the versatility of REC ionization was underlined in the literature for chromatographic detection [7].As an example of REC, the reactions at two different electron capture resonances (associative and dissociative) of nitrobenzene are shown below [8].In Reaction 1, capture of zero energy electrons is an efficient process for producing intact molecular ions. In addition, through Reaction 2, higher electron energy resonances are also available for electron capture producing the NO 2 Ϫ fragment. These higher energy resonances can improve the analytical selectivity of REC in the case of compound mixtures.Two instruments capable of REC ionization, suited for gas phase studies, are the throchoidal electron monochromator [9] and the reversal electron attachment detector (READ) [10]. The electron monochromator uses crossed electric and magnetic fields to force different trajectories on electrons with different energies. An offset exit aperture allows monoenergetic electrons to pass into the source region of a mass spectrometer. A more detailed discussion can be found in the reference by Laramee et al. [9]. READ operates by

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Section: Demonstration Of Percisupporting

confidence: 71%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Photoelectron resonance capture ionization (PERCI): A novel technique for the soft-ionization of organic compounds

LaFranchi

Petrucci

2004

J. Am. Soc. Mass Spectrom.

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“…used Illenbergers design to further improve the use of the EM in MS applications [5,6]. This device was reported to allow the ionization energy to be precisely controlled to ± 0.3 eV with ion currents only slightly below those observed for electron ionization.…”

Section: Introductionmentioning

confidence: 99%

Theory and Application of Dissociative Electron Capture in Molecular Identification

Havey

Eberhart²,

Jones³

et al. 2006

J. Phys. Chem. A

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The coupling of an electron monochromator (EM) to a mass spectrometer (MS) has created a new analytical technique, EM-MS, for the investigation of electrophilic compounds. This method provides a powerful tool for molecular identification of compounds contained in complex matrices, such as environmental samples. In particular, EM-MS has been applied to the detection of nitrated aromatic compounds, many of which are potent mutagens and/or carcinogens and are considered environmental hazards. EM-MS expands the application and selectivity of traditional MS through the inclusion of a new dimension in the space of molecular characteristicsthe electron resonance energy spectrum. EM-MS also enhances detection sensitivity as well because the entire electron flux of the proper energy can be delivered into the negative ion resonance that is analytically most useful to solving the problem at hand. However, before this tool can realize its full potential, it will be necessary to create a library of resonance energy scans from standards of the molecules for which EM-MS offers a practical means of detection. Unfortunately, the number of such standards is very large and not all of the compounds are commercially available, making this library difficult to construct. Here, an approach supplementing direct measurement with chemical inference and quantum scattering theory is presented to demonstrate the feasibility of directly calculating resonance energy spectra. This approach makes use of the symmetry of the transition-matrix element of the captured electron to discriminate between the spectra of isomers. As a way of validating this approach, the resonance values for twenty-five nitrated aromatic compounds were measured along with their relative abundance. Subsequently, the spectra for the isomers of nitrotoluene were shown to be consistent with the symmetry-based model. The initial success of this treatment suggests that it might be possible to predict negative ion resonances and thus create a library of EM-MS standards.2

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Collisional stabilization of negative ions produced by a monoenergetic electron beam

Berkout

Mazurkiewicz

Deinzer

1999

Rapid Commun. Mass Spectrom.

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The effect of different buffer gases on the intensity of negative ions was studied using a gas chromatography/electron monochromator mass spectrometer (GC/EM-MS). The buffer gas was introduced into the ion source not to moderate the electron energies, but specifically to investigate the process of collisional stabilization of negative ions. Three different designs of ion source were tested to study this phenomenon. It was found that collisional stabilization has a profound effect on the intensity of molecular radical anions and begins to play an important role at buffer gas pressures in the order of 10 mTorr. By using a partitioned ion-forming chamber, it was shown that for optimum stabilization to take place the buffer gas should be present in the region of negative ion formation. The gases possessing internal degrees of freedom which are capable of accommodating the excess energy of short-lived excited molecular anion states showed the largest increase in molecular radical anion intensities. At the same time helium, a widely used GC carrier gas, showed sufficient stabilization properties to allow detection of the molecular radical anions of typical electron-capturing molecules with positive electron affinities.

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Electron monochromator-mass spectrometer instrument for negative ion analysis of electronegative compounds

Cited by 44 publications

References 69 publications

Photoelectron resonance capture ionization (PERCI): A novel technique for the soft-ionization of organic compounds

Photoelectron resonance capture ionization (PERCI): A novel technique for the soft-ionization of organic compounds

Theory and Application of Dissociative Electron Capture in Molecular Identification

Collisional stabilization of negative ions produced by a monoenergetic electron beam

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