Metastable Atom Bombardment Ionization

Metastable atom bombardment (MAB) is a novel ionization method for mass spectrometry invented by Michel Bertrand s group at the University of Montreal, Quebec, Canada, and described by Faubert et al.38 For the identification of bacteria by MS, MAB has a number of significant advantages relative to more familiar ionization techniques. Electron ionization (El) imparts so much excess energy that labile biomolecules break into very small fragments, from which the diagnostic information content is limited since all... 

Besides El, Cl, FI or FD techniques for generating ions in the mass spectrometer, some other ionization techniques have been reported. One such technique is metastable atom bombardment (MAB), which Is based on Penning ionization. In MAB a metastable ion beam generated outside the ion volume is used to bombard the sample. The energy available for ionization is discrete (quantified) and can be fixed by the choice of the rare gas used in the atom gun (He, Ne, Ar, Kr, Xe). This energy ranges from 8 to 20 eV. 

Moore et al. (2004) reported on the use of metastable atom bombardment (MAB) ionization and HRMS in the positive ion mode for the detection of CPs [34]. Using an inert gas like argon, MAB ionization generates ions via an electrophilic reaction of a metastable atom with the analyte of interest. Figure 10 shows a comparison of ECNI and positive ion MAB mass spectra. 

Moore S, Vromet L, Rondeau B (2004) Comparison of metastable atom bombardment and electron capture negative ionization for the analysis of polychloroaUcanes. Chemosphere 54 453 59... 

Ikonomou, M., Chromatographic and ionization properties of polybrominated diphenyl ethers using GC/high resolution MS with metastable atom bombardment and electron impact ionization. Anal. Chem., 74, 5263-5272, 2002. 

Metastable atom bombardment (MAB) is another suitable ionization option for gas-phase organic compounds [11,12]. In this approach, ionization occurs through Penning processes of the type shown in reactions (2.21) and (2.22) by bombarding the sample with a beam of metastable species. The process depicted in reaction (2.21) involves an electrophilic reaction of the metastable atom (A ) to produce an odd-electron molecular ion of the analyte. The excitation energy of A must exceed the IE of the analyte molecule. With much higher excitation energy, dissociative ionization process also takes place [reaction (2.22)]. 

Time required for extraction with SPE cartridges, chromatographic separation and LC-MS/MS determinations are too long. Therefore, a method using selective ionization of metastable atom bombardment (MAB) has been developed in order to... 

Liquid chromatography-electrospray ionization-time-of-flight-mass spectrometry. Pyrolysis-metastable atom bombardment-time-of-flight-mass spectrometry. 

Jamin, E., Chevolleau, S., Touzet, C., Tulliez, J., and Debrauwer, L. 2007. Assessment of metastable atom bombardment (MAB) ionization mass spectrometry for the fast determination of heterocyclic aromatic amines in cooked meat Anal. Bioanal. Chem. 387 2931-2941. 

Some mild methods of ionization (e.g., chemical ionization. Cl fast-atom bombardment, FAB electrospray, ES) provide molecular or quasi-molecular ions with so little excess of energy that little or no fragmentation takes place. Thus, there are few, if any, normal fragment ions, and metastable ions are virtually nonexistent. Although these mild ionization techniques are ideal for yielding molecular mass information, they are almost useless for providing details of molecular structure, a decided disadvantage. 

McLafferty et al. (37) studied the collisionally activated dissociation (CAD) of the ions resulting from the fast-atom bombardment ionization of cyano- and methylcobalamins, using a tandem mass spectrometer. They showed that mlz 1329 is produced only from the quasi-molecular ion. Similar CAD spectra are produced by both the quasi-molecular ions and the 1329 peak, indicating that essentially all fragmentation arises from this latter ion. CAD spectra produced for the 1329 ion derived from methylcobalamin or vitamin B12 coenzyme are also similar. This is consistent with the work of Taylor (10), who used linked-scan metastable ion techniques in a conventional double-focusing mass spectrometer to show the same thing. The sequential... 

Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) play an important role in the identification of unknown compounds. Different ionization techniques have been used in studying isothiazole derivatives, such as electronic ionization (El), desorption chemical ionization (DCI), fast atom bombardment (FAB), field desorption (FD), and chemical ionization (Cl). Different MS/MS experiments have been described, such as investigation of metastable and collision-induced dissociations to study isothiazoles gas-phase ion chemistry. In addition, MS and MS/MS have been used to differentiate isothiazole isomers differing in the position of endocyclic groups or exocyclic substituents <1998THS(2)471, 1999THS(3)369, 2000THS(4)405>. 

See also Chemical Ionization in Mass Spectrometry Fast Atom Bombardment Ionization in Mass Spectrometry Fragmentation in Mass Spectrometry Ion Structures in Mass Spectrometry Ion Trap Mass Spectrometers Ionization Theory Ion Energetics in Mass Spectrometry Ion Collision Theory Metastable Ions Quadrupoles, Use of in Mass Spectrometry Sector Mass Spectrometers Statistical Theory of Mass Spectra Time of Flight Mass Spectrometers. 

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