Metastable ions decay

In mass spectra of borabenzene metal complexes, ions of type [M(C5H5B)]+ are commonly observed [Co(CsH5B)]+ decays via loss of an uncharged C5H5B fragment as evidenced by the observation of a metastable ion peak (7). 

Note In particular the MALDI-TOF community has coined some sort of an own terminology, e.g., in-source decay (ISD) for all fragmentations occurring within the ion source, post-source decay (PSD) instead of metastable ion dissociation and fragment analysis and structural TOF (FAST) for the specific mode of operation of a ReTOF to detect metastable ions. 

The isomeric o-, m- andp-chloroaniline, which under El give identical spectra, have been characterized by means of resonance-enhanced multiphoton ionization (REMPI) combined with a linear TOF mass spectrometer151. The method is based on the difference the three isomers display in the shapes of their metastable parent ion decays. 

Several desorphon and spray ionization methods can be used to convert S5mthehc polymers into intact molecular or quasimolecular ions (vide supra), whose exact m/z ratio identifies the composition of the polymer. For structural informahon about the polymer, the dissociation behavior or ion-molecule reactions of the polymer ions must be studied. Such reactions, which rarely take place during the soft ionization processes necessary to generate intact gas phase ions from synthetic macromolecules, are most conveniently assessed by tandem mass spectrometry (MS/MS). With MS/MS, a specific precursor ion is mass-selected, so that its reactivity can be investigated without perturbation from the other ions formed upon ionization. The reaction products of this ion are then mass-analyzed and collected in the MS/MS spectrum. MS/MS studies on polymer ions have so far focused on their spontaneous ("metastable") or collision-induced fragmentation. The fragments arising in these reactions are displayed in metastable ion (MI) or collisionally activated dissociation (CAD) spectra, respectively. Customarily, MI spectra acquired with a TOF mass analyzer have been named "postsource decay (PSD)" spectra similarly, CAD is often referred to as CID (collision-induced dissociation). ... 

TOP analyzer equipped with a rellectron (Section 6.4.7) in an equivalent metastable ion mode (so-called postsource decay, PSD), this operating mode is too tedious and insensitive to be useful for trace quantitation. 

A linear TOF analyzer can not provide any MS/MS information but a reflection instrument can provide fragment ion spectra of metastable ions that fragment (either spontaneously or via laser photodissodation) while in flight between the final acceleration grid and the reflectron entrance (Weickhardt 1996). However, this post-source decay technique has never been used for quantitative trace analysis. 

MS and proton NMR spectroscopy have mainly been used for structure elucidation of isolated compounds. However, there are some reports on mass spectrometric analyses of essential oils. One example has been presented by Griitzmacher (1982). The depicted mass spectrum (Figure 2.9) of an essential oil exhibits some characteristic molecular ions of terpenoids with masses at miz 136, 148, 152, and 154. By the application of a double focusing mass spectrometer and special techniques analyzing the decay products of metastable ions, the components anethole, fenchone, borneol, and cineole could be identi ed, while the assignment of the mass 136 proved to be problematic. 

Zampedri et al. have shown that, in (100 — x)Si02-(x)Ti02-lEr03/2 planar waveguides prepared by sol-gel route, for x < 12, about 65% of the Er + ions in the Ii3/2 metastable state decay exponentially with a lifetime of about 8 ms (Zampedri, 2003). 

The ions in excited levels possessing allowed electric dipole transitions decay very close to the foil and the beam at the detectors consists only of ground state and metastable ions. Ions in the metastable 2 decay by the emission... 

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