Triply charged ion

We have discussed the triply charged ion Fe+++ in aqueous solution. Let us consider now the water molecules that are in contact with such an ion, and let Fig. 50a depict one such H2O molecule. The protons in the H2O molecule will be repelled by the large positive charge of the Fe+++ ion—will be so strongly repelled that it is possible that, sooner or later, the thermal agitation will be sufficient to transfer a proton to a... 

If an ion is doubly charged, wc multiply its concentration by 2 in the charge balance equation, and likewise for triply charged ions. 

Depending on the analyte and on the energy of the primary electrons, doubly and even triply charged ions can also be observed. [20] In general, these are of low abundance. 

While the doubly charged ion, is an even-electron ion, the triply charged ion, again is an odd-electron ion. In addition, there are several other events possible from the electron-neutral interaction, e.g., a less effective interaction will bring the neutral into an electronically excited state without ionizing it. 

In general, a mass separation of 0.5-0.7 Da would be indicative of a doubly charged ion. Similarly, a separation of only 0.3 mass units would indicate a triply charged ion. 

The main features of the mass spectrum of benzo[6]thiophene have been established by Porter,121 using the spectrum of 3-deutero-benzo[6]thiophene for comparison purposes. Triply charged ions have been detected in the mass spectra of benzo[6]thiophene and its 2- and 3-methyl derivatives.126... 

Figure 5.11 displays the analysis of a mixture of peptides from ovalbumin obtained by CE/MS coupled to ESI. The spectrum shown is a mean of the spectra acquired during the elution of the indicated broad peak. It corresponds to a mixture of doubly or triply charged ions of several glycopeptides [27]. The displayed structures were actually deduced from MS/MS fragmentation spectra of these multiply charged ions. 

Ferric. Pertaining to iron combined in the trivalent state or in the form of the triply charged ion Fe+++. 

Since the successive constants are lower than the preceding ones, the second (or third) ionization does not contribute appreciably to the hydronium ion concentration of the solution of acid in water, but is the only source of the doubly (or triply) charged ion. 

It may be also mentioned that phenothiazine is one of the rare organic compounds in which mass spectrometry has revealed triply charged ions. ... 

Such a definition of terms is necessary in order to avoid confusion of meaning. For example, reference is often made to the trivalent ion of aluminium. If by this it is meant that the aluminium ion is forming three covalent bonds, then the statement is correct and the aluminium ion is trivalent but if, however, the statement is meant to denote the fact that aluminium has lost three electrons, then it is a triply charged ion and not trivalent since its electronic configuration will be that of an inert gas and it will have no unpaired electrons. The correct description of aluminium in this case is that it is a triply charged, zerovalent ion. The necessity for this careful definition of valency will become apparent in the following discussion, where it will often be necessary to refer simultaneously to the charge and covalency of an ion. 

In general, MALDI of samples fixed to membranes resulted in no loss of mass resolution or mass range. Spectra were extremely reproducible, and could usually be acquired at a lower threshold laser intensity. Figure 1 shows a peptide and protein mixture desorbed from each of the 5 tested membranes. All membranes except the CIS extraction disk produced well resolved spectra. Higher masses were better resolved in samples fixed to polyethylene membranes, while lower masses were better resolved by fixing samples to the Type 61 disposable IR card. Doubly and triply charged ions formed more readily upon desorption/ionization from all the membranes tested, than from stainless steel surfaces. 

The accurate mass measurement was performed on a Micromass AutoSpec SE mass spectrometer using electrospray ionization on the triply charged ion of a cofactor-containing peptide (sample 2). Doubly charged ions of bradykinin (m/z 530.7885) and gramicidin S (m/z 571.3608) were used as calibration standards. Leu-enkeph in (MH+ at m/z 556.2771) was also included to verify the accuracy of the mass measurement. The monoisotopic molecular mass of this peptide was established by the mean [M-i-3H]3+ value obtained from four separate injections. Elemental compositions of the crosslinked residue were obtained by computer calculations. 

Calculations such as those in Example 22-2 permit us to find the differences in standard electrode potentials theoretically needed to determine one ion without interference from another. These differences range from about 0.04 V for triply charged ions to approximately 0.24 V for singly charged species. 

In early work it was recognized that the seledion of the sampling zone in the plasma and the aerosol carrier gas flow may strongly influence the occurrence of cluster ions and doubly charged analyte ions [502, 503]. This is clearly demonstrated by the results for lanthanum, where even doubly and triply charged ions may be expected in the argon plasma. This necessitates specific optimization of the power and especially of the carrier-gas flow, which influence both temperature and residence times of the sampled substance in the plasma. This is documented e.g. for the intensities of the signal for the ArO+ and the Cu+ ions in Fig. 113 [504]. 

Iron forms many compounds. In some of them, such as ferrous oxide, FcO, the iron atom is said to be bivalent in ferrous oxide it may be described as having transferred two electrons to the oxygen atom, leaving it a doubly charged ion, Fe++. In other compounds, such as ferric oxide (the mineral hematite), Fe203, the iron atom has valence three, corresponding to the triply charged ion, Fe+++. The ferric compounds are more stable than the ferrous compounds. 

Fig. 5.8. ESI FTICR mass spectrum of the supramolecular rhomb s (S,S,S,S) enantiomer. The intense signal at m/z 662 represents the doubly-charged complex [M—2 HNO3-2 NOs]. The insets show the experimental (top) and calculated (bottom) isotope patterns of the doubly-charged ion [M—2 HNO3-2 NO3]2 (right inset) and the triply-charged ion [M—I—IN O3—3 NO3] + (left inset). The inset of the doubly-charged species at m/z 662 is superimposed by another isotope pattern of a triply-charged 3 3 complex, that is also included in the calculation.

Figure 11.2. Analysis of undecapeptide libraries 0/XlirNH2 by electrospray mass spectrometry. Spectra of four groups of libraries are superimposed. Each group is expected to show identical mass patterns. The libraries are characterized by one defined amino acid (K, D, L, W) in different sequence positions. The positively charged libraries K/X, -NH2 show, as expected, striking intensities of triply charged ions. Additional experiments are necessary to explain the shift in the mass pattern for DXurNH2 characterized by the negatively charged amino acid D in the N-terminal position.

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