Electron impact mass

The electron impact mass spectrometric fragmentations of (E)-3- and ( )-4-styryl-pyridazines show that the intensity ratio of the M and (M -1)" ions, the general degree of fragmentation and the elimination pathways of nitrogen are the most characteristic features distinguishing between the two isomeric compounds (81JHC255). 

Electron impact mass spectrometry has been employed to study the fragmentation patterns of isoxazolylmethyl- and bis(isoxazolylmethyl)-isoxazoles and the results are in agreement with proposed pathways (79AC(R)8l). Electron impact studies of nitrostyryl isoxazole (6) show fragmentation in a variety of ways. The standard loss of NO2 from the molecular ion... 

Diphenylthiirene 1-oxide and several thiirene 1,1-dioxides show very weak molecular ions by electron impact mass spectrometry, but the molecular ions are much more abundant in chemical ionization mass spectrometry (75JHC21). The major fragmentation pathway is loss of sulfur monoxide or sulfur dioxide to give the alkynic ion. High resolution mass measurements identified minor fragment ions from 2,3-diphenylthiirene 1-oxide at mje 105 and 121 as PhCO" and PhCS, which are probably derived via rearrangement of the thiirene sulfoxide to monothiobenzil (Scheme 2). 

Sixteen non- to trimethyl-substituted thiazoloquinolines of these types were inveshgated under electron impact mass spectra thiazoloquinolines lose carbon monosulhde (CS) from the thiazole and HCN from both heterocyclic nuclei. When 2-methylthiazoloquinolines fragment, the hydrogen radical and a loss of a neutral... 

An on-line chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (LC-APCI/MS/MS) methods was developed for rapid screen of pharmacokinetics of different drugs, including 5 (98RCM1216). The electron impact mass spectrum of 5 and ethyl 9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7Ff-pyrido[l,2,3- fe]-l,4-benzoxazine-6-carboxylate was reported (97MI28). Electron impact/Fourier transform... 

In the electron impact mass spectrum of C02, 0+ ions are formed with an appearance potential (AP) 19.1 e.v. according to the process ... 

We conclude, that the ionization processes by charge exchange in a perpendicular type apparatus or using electron impact at high energy are substantially similar, and therefore it is possible to calculate the electron impact mass spectrum from charge exchange observations by... 

Description glycosidic cleavage to form an oxonium ion charge retained on nonreducing end positive-ion mode only often referred to as A -type cleavage, because of similarity to one of the cleavages seen in electron impact-mass spectrometry. 

Figure IQ Postulated structure for the major fragment ion of xenognosin B under electron impact mass spectrometry.

Section 6.4 deals with other EI-MS analyses of samples, i.e. analyses using direct introduction methods (reservoir or reference inlet system and direct insertion probe). Applications of hyphenated electron impact mass-spectrometric techniques for poly-mer/additive analysis are described elsewhere GC-MS (Section 7.3.1.2), LC-PB-MS (Section 7.3.3.2), SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

DRI Differential refractive index EI-MS, El MS Electron impact mass spectrometry... 

Purdon JG, Pagotto JG, Miller RK. 1989. Preparation, stability, and quantitative analysis by gas chromatography and gas chromatography-electron impact mass spectrometry of tert-butyldimethylsilyl derivatives of some alkylphosphonic and alkyl methylphosphonic acids. J Chromatogr 475 261-272. 

The electron impact mass spectrum of methyl isobutyrate, 27, contains a signal for a [M—CH3]+ ion. 2H- and 13C-labelling clearly establishes that the eliminated methyl radical originates exclusively from the intact PCH3 group (6)12,13,1 . 

The analysis of chemicals by reference to a set of library mass spectra was facilitated by the establishment almost 40 years ago of databases such as the NIST/EPA/NIH reference library of electron impact mass spectra (http //www.nist.gov/srd/nistla.htm). Experimentally derived mass spectra are compared to spectra in the library, and the matches are graded by various algorithms. This comparison is valid because electron impact ionization requires that the sample be vaporized and thus isolated from its sampling history. 

Figure 9 (A) electron impact mass spectrum of the peak at 9.97 min (see Figure 8) (B) MS of a reference standard of triclosan.

Lebedev et al. used electron impact mass spectrometry to induce the intramolecular cyclizations of dithiocarbamates of polyhalopyridines forming bis-l,3-dithiolo[4,5- 4, 5 -tf]pyridines, that are obtained by reaction in solution. Identical products were obtained under electron impact mass spectrometry (MS) conditions <1997JMP728>. 

Similar experiments on a large number of transition metal carbonyls have shown that this process favors dissociation to and detection of metal clusters or atoms. Since most metal-(CO)n photofragments are themselves subject to efficient dissociation, MPI experiments do not identify the primary photoproducts. This situation contrasts sharply with electron impact ionization where the parent ion is usually formed and daughter ions are seen as a result of parent ion fragmentation. Figure 4 shows the electron impact mass spectrum of Mn2(C0) Q (33). for comparison with the MPI mass spectrum of Figure 3. 

The six- and seven-membered rings S5NR and S6NR are yellow oils that exhibit molecular ions in their electron-impact mass spectra. The nine- and ten-membered rings S8NH and S9NH form photosensitive, pale yellow crystals that are soluble in CS2. The 12-membered ring SnNH has only been characterized by spectroscopic methods.207... 

The low resolution electron impact mass spectral pattern of bromocriptine mesilate (fig. 7) corresponds quite nicely to those of the other non- and dihydrogenated ergot alcaloids (12, 13 and lit. quoted herein). 

Figure 7. Low Resolution Electron Impact Mass Spectrum of Bromocriptine Mesilate...

Figure 14. Electron impact mass spectrum of CTC-HC1. Instrument Varian MAT 311 source...

The medium resolution, electron-impact mass spectrum of griseofulvin (Figure 4) was run on a Varian-Mat CH-5 Mass Spectrometer. Instrumental conditions were Electron Energy 70eV Source Temperature 250°C Sample Probe Temperature 140°C. 

An electron impact mass spectrum of calcium leuco-vorin has not been obtained because the compound is not sufficiently volatile. It would be difficult to isolate the free acid without first dehydrating the compound. Due to its ionic nature, calcium leucovorin will not dissolve in common silylating reagents. Field desorption, another mass spectral technique, generally lends itself more to compounds like leucovorin. Indeed, this technique has been applied successfully to methotrexate and other folic acid analogs.1 ... 

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