Chemical self-ionization

Tire self-chemical ionization reaction of CS2 under chemical ionization conditions (approx. 1 Torr) generated 83, which sulfurized pyridine (97MI1) and nitriles (97JPC6970) to give the corresponding cation radicals 61 and 62, respectively. Ab initio calculations on 83 at the G2 (MP2, 8VP) level revealed that the ylide radical cation form 63 is more stable than the dithiiranethione radical cation form (64) by 42 kJ/mol (97JPC6970). 

Eichelberger, J.W. and Slivon, L.E. Existence of self chemical ionization in the ion-trap detector. Finnigan MAT IDT 48. 

FIGURE 4. Self-chemical ionization FT-ICR mass spectmm of diethylzinc. Electron energy 70 eV diethylzinc neutral reagent pressure 5x10 Torr. Reproduced by permission of John Wiley Sons Ltd. from Reference 25... 

The analytically important features of Fourier transform ion cyclotron resonance (FT/ICR) mass spectrometry (1) have recently been reviewed (2-9) ultrahigh mass resolution (>1,000,000 at m/z. < 200) with accurate mass measurement even 1n gas chromatography/mass spectrometry experiments sensitive detection of low-volatility samples due to 1,000-fold lower source pressure than in other mass spectrometers versatile Ion sources (electron impact (El), self-chemical ionization (self-Cl), laser desorption (LD), secondary ionization (e.g., Cs+-bombardment), fast atom bombardment (FAB), and plasma desorption (e.g., 252cf fission) trapped-ion capability for study of ion-molecule reaction connectivities, kinetics, equilibria, and energetics and mass spectrometry/mass spectrometry (MS/MS) with a single mass analyzer and dual collision chamber. 

In the internal ionization mode, ions are formed, stored, and excited resonantly to the point of ejection inside the ion trap in the presence of neutral sample molecules. Primary fragment ions confined in the ion trap experience the flow of neutral sample molecules through the ion trap for a period of time that varies from cfl 2 ms to ca 200 ms. The longer is this period of time, the greater is the probability of the occurrence of undesirable ion/molecnle reactions this process is known as self-chemical ionization, or self-Cl [20], Typically, self-CI will create [M -H H] + ions due to proton transfer. However, adduct ion peaks may be formed when an alkyl group is transferred. The self-CI process may affect library-search results of those compounds because the majority of mass spectra in mass-spectral libraries were acquired with quadru-pole mass filters or magnetic sector mass spectrometers wherein self-CI does not... 

J.W. Eichelberger and L.E. Slivan, Existence of Self-Chemical Ionization in the Ion-Trap Detector, Finnegan MAT IDT Publication 48. 

McLuckey SA, Glish GL, Asano KG, Van Berkel GJ. Self chemical ionization in an ion trap mass spectrometer. Anal Chem. 1988 60 2312-4. 

Smith, P.A., Jackson Lepage, G.R., Savage, P.B., et al, 2011b. Use of a hand-portable gas chromatograph-toroidal ion trap mass spectrometer for self-chemical ionization identification of degradation products related to 0-ethyl-S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX). Anal Chim. Acta 690, 215-220. 

Pulsed-Valve Cl and CID-Exneriments. Chemical Ionization (Cl), self-CI (SCI), and direct or desorption Cl (DCI) experiments in FTMS can be done equally well with the differentially-pumped external ion source described below, or with a pulsed-valve single cell arrangement (5,6). In our experiments, we admit a pulse of reagent gas via a piezoelectric pulsed valve with a minimum opening time of about 2.5 ms (7). Unlike solenoid pulsed valves, the performance of piezoelectric pulsed valves is not disturbed by the strong magnetic field of 4.7 Tesla. 

The suggested structure of the photoinduced form of naphtoquinone methide was confirmed by identification of this compound at 77 K, the coincidence of experimental and calculated Pariser-Parr-Pople self-consistent field chemical ionization (PPP SCF Cl) spectral characteristics, and the sharp change in the rate of the dark relaxation from the photoinduced state to the initial form (by four orders of magnitude) upon passage from hydrocarbon to aprotic hydrogen-bond acceptor solvents.11... 

The detection of chiral recognition with a mass spectrometer was reported first in 1977 by Fales and Wright.357 Their study showed that the chirality of dialkytartrates (T) strongly influences the stability of their diastereomeric proton-bound dimers, generated by isobutane chemical ionization (CIMS) of their racemic mixtures.358,359 In order to differentiate the protonated species of the homochiral self-dimers... 

An important aspect of the chemical ionization technique is the fact that with different kinds of reactant ions different kinds of reactions will be involved in the production of the chemical ionization mass spectra. Thus, for example, if is used as a reactant, the reaction occurring is proton transfer, and the chemistry involved may be looked upon as an even-electron, gaseous acid-base chemistry. On the other hand, if N2 is used as a reactant ion, electron transfer occurs, and one then has an odd-electron, oxidation-reduction chemistry. It is self-evident that by using different reactant ions the intensity of the chemical ionization reaction can be varied that is. 

Because the ion trap contains ions of all values of m/z at the same time (as well as neutral molecules that were not ionized prior to entering the trap), ion trap mass analyzers are also sensitive to overload and ion-molecule collisions that complicate the resulting spectrum. Recall that not all of the sample molecules get ionized—many remain uncharged. These neutral species move in a random path in the ion trap, resulting in collisions with ions as the ions oscillate in their stable trajectories. These collisions result in chemical ionization-type ionization events (Equation 3.20). This is sometimes referred to as self-CI. 

Dependence of tt complex binding constants upon nucleoside ionization potentials for ( ) uridine, ( ) thymidine, (A) cytidine, (o) adenosine, (O) guanosine, and (A) N,N,-dimethyladenosine. Panel A shows association constants for the binding of nucleosides to riboflavin. Panel B shows association constants for the self association of nucleosides. (Reproduced from Ref. 82. Copyright 1981, American Chemical Society.)... 

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