Chemical ionization mass identified

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). 

This system was studied by Schwartz. Toluene at 10 ppm, nitric oxide at 1 ppm, and nitrogen dioxide at 1.2 ppm were irradiated with ultraviolet lamps in a 17-m batch reactor for 270 min. Collected aerosols were successively extracted with methylene chloride and then methanol. The methylene chloride extract was fractionated into water-soluble and water-insoluble material, and the latter fraction was further divided into acidic, neutral, and basic fractions. The acidic and neutral fractions were analyzed by gas chromatography and chemical-ionization mass spectrometry the compounds identified are shown in Figure 3-7. The two analyzed fractions represented only about 5.5% of the total aerosol mass. It is noteworthy that classical nitration of an aromatic ring appears to... 

Laser-flash photolysis of (203) in solution affords the ketene (204) and this is the first time that this ketene has been observed using time-resolved IR spectroscopy, Although other workers have previously reported the formation of this species. The present work reports the kinetics of the reaction of the ketene with water, methanol and diethylamine. The products obtained from the irradiation of a series of AT-acetoacetyl-a-amino acids have been identified by gas chromatography and chemical ionization mass spectrometry. ... 

Figure 2. Crown ethers identified by chemical ionization mass spectroscopy for EO/THF polymerization using Nafion perfluorosulfonic acid resin as catalyst.

Identified by Heins et al. (1966) in the headspace over coffee beans by one of the first capillary-GC/MS coupling. The ion M + 1 (mjz = 117) was one of the ions used by Dyszel (1985) when using thermo-gravimetric analysis/atmospheric pressure chemical ionization mass spectrometry (TGA/APCIMS) for determining the origin of green coffee. It was found after simultaneous distillation-extraction and analysis by GC/MS by Spadone et ai (1990) in a Puerto Rico Rio coffee, but not in a healthy variety. It was one of the compounds emitted by fresh red coffee berries in two robusta varieties (Mathieu et al., 1996), and was found to decrease if the berries were left on the plant after the red stage (Mathieu et al., 1998). 

A mass spectrometric investigation of NO2/O3/O2 mixtures with chemical ionization has identified the NO5+ cation from the reaction of NO2+ with ozone. The decomposition products NO4+ and NO3+ indicate an O NOa connectivity of NO5+ and its decomposition products. 

The product ions generated by chemical ionization are stable, even-electron species, with relatively little excess energy compared to those generated by electron impact. The chemical ionization mass spectrum, therefore, is characterized by the presence of a few intense molecular ion adducts with very little further fragmentation from which the sample molecular mass is readily identified from the m/z value of the molecular ion adducts. The type of molecular ion adduct formed depends mainly on the sample composition and the identity of the reagent gas. 

Homogenized garlic was extracted by SF-CO2 and the major thiosulfinates were characterized with liquid chromatography/ atmospheric pressure chemical ionization mass spectroscopy (LC/APCI/MS) [59]. In addition to the thiosulfinates, small quantities of ajoene were also found in the SF extracts of garlic homogenates. The identified thiosulfinates are listed in Table (1). 

Stereochemical studies based on C-nuclear magnetic resonance spectroscopy ( C-NMR) showed the presence of eight cis and trans allylic hydroperoxides (Table 2.1). To determine the isomeric distribution of allylic hydroxyooctadecenoate derivatives, cis and trans fractions were separated by silver nitrate-thin layer chromatography (TLC), a procedure that separates according to the number, position and geometry of double bonds, and they were hydrogenated prior to GC-MS analyses of the TMS ether derivatives. More recently, the six major hydroperoxide isomers of methyl oleate were partially separated by silica HPLC, and identified by chemical-ionization mass spectrometry and IH NMR (Table 2.1). These hydroperoxide isomers were better separated as the hydroxy octadecenoate derivatives by the same silica HPLC method and re-analysed by GC-MS. 

As with analytical OPLC, off-line and on-line methods can be distinguished in preparative OPLC applications. In the off-line OPLC method, the steps of preparation after development are similar to conventional TLC methods drying, scraping of the sorbent layer, elution, and crystallization. Phorbol diester constituents of croton oil were identified by off-line OPLC separation followed by extraction and chemical ionization mass spectrometry (CI-MS) (90). The on-line method is more effective for preparative applications because time-consuming scraping and elution can be eliminated. 

Electron impact ionization (El) and chemical ionization (Cl) mass spectrometry using a direct insertion probe continue to be used for molecular weight confirmation and identification of purified retinoids. Retinoid fragmentation patterns are useful for identification, especially when mass spectra of unknown compounds are compared to those of reference standards. For example. Buck et al. (284) used El and Cl mass spectrometry with a direct insertion probe to identify retinol as an essential growth factor for the culturing of human B cells, and Lakshman et al. (285,286) used El mass spectrometry to identify retinal O-ethyloxime. Barua (287) reported the desorption chemical ionization mass spectra of retinoyl P-glucuronide after methylation with diazomethane and pertrimethylsilylation. Molecular ions were detected in very low abundance. 

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