Mass spectrometry , gas-phase

Table 10. Thermodynamic data for individual clustering steps in derived by high pressure mass spectrometry gas-phase solvation of H+, ...

See also Fragmentation in Mass Spectrometry Gas Phase Appiications of NMR Spectroscopy ion Dissociation Kinetics, Mass Spectrometry ion Energetics in Mass Spectrometry Photoionization and Photodissociation Methods in Mass Spectrometry Time of Fiight Mass Spectrometers. 

Prior to being sampled by the mass spectrometer, analytes freed from electrospray droplets enter a region at atmospheric pressure that contains a number of solvent molecules and other vapor-phase species. Proton transfer between the analytes of interest and these solvent molecules can sometimes affect the species detected with electrospray mass spectrometry. Gas-phase proton transfer has been shown to alter the charge states of proteins analyzed with electrospray mass spectrometry,and in some specific cases it may be a source of selectivityin electrospray analysis of small molecules,... 

Thienpont LM, Verhaeghe PG, Van Brussel KA, De Leenheer AP. Estradiol-17 beta quantified in serum by isotope dilution-gas chromatography-mass spectrometry reversed-phase C18 high-performance liquid chromatography compared with immuno-affinity chromatography for sample pretreatment. Clin Chem 1988 34 2066-9. 

The ToF mass analyzer is the fastest, has a broad m/z range, is one of most sensitive mass spectrometry analyzers available, and is well-suited to imaging applications. In ToF mass analysis, gas-phase ions produced by a pulsed ion source are accelerated in a high vacuum by an electric field. After being accelerated, the ions enter a field-free region between the ion source and detector at a vdocily related to their m/z ratio, with lower-m/z ions reaching the detector earlier than higher-m/z ions. 

Other techniques for predicting the cetane number rely on chemical analysis (Glavinceski et al., 1984) (Pande et al., 1990). Gas phase chromatography can be used, as can NMR or even mass spectrometry (refer to 3.2.1.l.b and 3.2.2.2). 

An important application of these results lies in the analysis of food flavorings using a combination of gas-phase chromatography and mass spectrometry (121, 122). Similarly, metabolic products of chlo-methiazole have been characterized (123). 

Hypochlorous acid and chlorine monoxide coexist in the vapor phase (78—81). Vapor pressure measurements of aqueous HOCl solutions show that HOCl is the main chlorine species in the vapor phase over <1% solutions (82), whereas at higher concentrations, CI2O becomes dominant (83). The equihbtium constant at 25°C for the gas-phase reaction, determined by ir and uv spectrophotometry and mass spectrometry, is ca 0.08 (9,66,67,69). The forward reaction is much slower than the reverse reaction. 

Solid-phase microextraction (SPME) was used for headspace sampling. The FFA were extracted from the headspace with PA, Car/PDMS, and CW/DVB fibers. It was examined whether addition of salt (NaCl) and decreasing the pH by addition of sulphuric acid (H SO ) increased the sensitivity. FFA were analyzed using gas chromatography coupled to mass spectrometry in selected ion monitoring. 

Sulfurous acid has never been isolated as a pure compound, although it has recently been detected in the gas phase by neutralization reionization mass spectrometry (NRMS) following the facile dissociative ionization (70 eV) of either diethyl sulfite or ethanesulfonic acid " ... 

This technique provides quantitative information about tautomeric equilibria in the gas phase. The results are often complementary to those obtained by mass spectrometry (Section VII,E). In principle, gas-phase proton affinities, as determined by ICR, should provide quantitative data on tautomeric equilibria. The problem is the need to correct the measured values for the model compounds, generally methyl derivatives, by the so-called N-, 0-, or S-methylation effect. Since the difference in stability between tautomers is generally not too large (otherwise determination of the most stable tautomer is trivial) and since the methylation effects are difficult to calculate, the result is that proton affinity measurements allow only semi-quantitative estimates of individual tautomer stabilities. This is a problem similar to but more severe than that encountered in the method using solution basicities (76AHCS1, p. 20). 

T. Hankemeier, A. J. H. Louter, J. Dalliige, R. J. J. Vreuls and U. A. Th Brinkman, Use of a drying cartridge in on-line solid-phase extraction gas cliromatography-mass spectrometry , 7. High Resolut. Chromaiogr. 21 450-456 (1998). 

D. Jahr, Determination of alkyl, chloro and mononiti ophenols in water by sample-acetylation and automatic on-line solid phase excaction-gas cliromatography-mass spectrometry , Chromatographia 41 49-56 (1998). 

Laali and Lattimer (1989 see also Laali, 1990) observed arenediazonium ion/crown ether complexes in the gas phase by field desorption (FD) and by fast atom bombardment (FAB) mass spectrometry. The FAB-MS spectrum of benzenediazonium ion/18-crown-6 shows a 1 1 complex. In the FD spectrum, apart from the 1 1 complex, a one-cation/two-crown complex is also detected. Dicyclo-hexano-24-crown-6 appears to complex readily in the gas phase, whereas in solution this crown ether is rather poor for complexation (see earlier in this section) the presence of one or three methyl groups in the 2- or 2,4,6-positions respectively has little effect on the gas-phase complexation. With 4-nitrobenzenediazonium ion, 18-crown-6 even forms a 1 3 complex. The authors assume charge-transfer complexes such as 11.13 for all these species. There is also evidence for hydride ion transfer from the crown host within the 1 1 complex, and for either the arenediazonium ion or the aryl cation formed from it under the reaction conditions in the gas phase in tandem mass spectrometry (Laali, 1990). 

Keywords retro-Diels-Alder fragmentation occurring in gas-phase, fragmentation in mass spectrometry... 

The substituted radical cations [Me2S.. SMe2], [Et2S. .SEt2] and [Et2S.. SMe2] (Fig. 4) have been studied by lilies, McKee and co-workers using a combined experimental/theoretical approach [127-129]. Mass spectrometry experiments on the gas-phase association reactions... 

The oxide S3O has been identified only in the gas-phase by means of neutralization reionization mass spectrometry [58]. The precursor ion SsO was generated by the following sequence of reactions ... 

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