Double charged ions

C9H7 ion from naphthalenes (may produce a double-charged ion at m/z 57.5)... 

When a multiply charged ion solvated by several solvent molecules is subjected to heating or to vibrational excitation due to collisions with inert neutrals, ion desolvation occurs by successive loss of single solvent molecules, as illustrated below, for a double-charged ion and solvent molecules SI ... 

As starting materials for organic metals, organic substances must correspond to several general requirements. Namely, both acceptors and donors must form redox systems, with the participation of not only ion-radicals but also double-charged ions, A + e —> A + e — A or D e —> D+ e — Ion-radicals play a role as mediators in these two-electron transfers. Each one-electron... 

Peptides carry single or charged ions based on their size, molecular weight, and the number of amino acid residues. In many cases, double-charged ions of peptides are predominant in mass spectrum. 

Ion radicals play a role as mediators in these two-electron transfers. Each one-electron step achieves a maximal rate, and both rate constants become close. Coulombic repulsion of positive (or negative) charges makes the double-charged ion formation difficult. Therefore, donors (or acceptors) are preferable for which some possibility exists to disperse the charge. Extension of the 77-system reduces intramolecular coulombic repulsion in the dianion state. Electron-donor (or electron-acceptor) substituents should be located at diametrically opposite sites of the molecule. Examples are ll,ll,12,12-tetracyano-9, 10-an-thraquinodimethane, TCNQ, DCNQI, and tetracyanobenzene. 

Unlike the case for other chlorinated compounds such as PCBs, double charged ions (at m/z values < MG/2 and with only 1 u between the chlorine isotope peaks) have not been mentioned for toxaphene components. The analysis of the GC/EI-MS fragmentation patterns allows a partial structure elucidation and the confirmation of the presence of a bornane skeleton. This knowledge facilitates a further structure elucidation by H-NMR spectroscopy [111]. 

With respect to the use of ESI-MS, this approach was pioneered by the group of Henion [57-58]. The intact protein is digested using trypsin into smaller peptides under neutral pH conditions at 37°C. Trypsin selectively cleaves the protein at the C-terminal side of Lys or Arg (Ch. 17.4.4). The tryptic digest is separated by RPLC-MS. ESI-MS generates abundant double-charge ions for the tryptic peptides. 

Figure 96. MIKE/CAD spectra of miz 134 ions, differentiating between tetrahydroquinoline and isoquinoline by the intensities of double charge ions [158,246],...

The sign will be + for cation-selective electrodes and - for those that are anion-selective. To be predominantly responsive to the concentration Ci, the factor Kij must be small. Where liquid membrane ion-selective electrodes responsive primarily to double-charge ions are concerned, and for interference by single-charge ions, equation (1) modifies to ... 

Single Charged Ions Double Charged Ions Triple Charged Ions... 

For aglycones the molecular ion almost invariably forms the base peak. Mass spectra of the 9,10-anthraquinone itself shows successive elimination of two molecules of carbon monoxide with strong peaks at m/z 180 (M-CO) and 152 (M-2 CO) (and strong double charged ions at m/z 90 and 76) which correspond to the molecular ions of fluorenone and biphenylene respectively ((Fig. (12)). 

Some compounds can be analyzed in both positive-ion and negative-ion mode. Because of the occurrence of intense alkah-metal cationization, it is sometimes preferred to perform the analysis in negative-ion mode. This was done for the analysis of the amphoteric or zwitterionic surfactant cocamidopropylbetaine (CAPB), which in the negative-ion mode predominantly shows [M-H], whereas in the positive-ion mode a range of ions is observed, inclnding monomeric, dimeric, and trimeric protonated, sodiated and potassiated molecnles, mixed double-charge ions, and a fragment ion [121]. 

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