Fast atom bombardment methods mass spectroscopy

The average DS as determined by these methods provides only the simplest characterization of these derivatives, and further analysis was necessary to characterize the mixture of SBE bands of different levels of substitution. Due to the presence of the anionic sulfonate substituent, it is possible to use capillary electrophoresis (23), to separate the SBE-CD substitution bands and to characterize the fingerprint of the composition (Fig. 10). Anion exchange chromatography (24) was utilized to isolate separate substitution bands (mono- to deca-derivatives) that were subsequently identified by NMR and fast atom bombardment mass spectroscopy (FAB-MS). 

Elemental analysis generally poses no problems because of the limited stability of the compounds and the formation of elemental gold in decomposition and combustion, which does not form carbides, nitrides, or other interstitial phases. Atomic absorption and inductively coupled plasma spectroscopy are presently the methods of choice for An estimation. Many organogold compounds are sufficiently volatile to allow registration of good mass spectra by gas-phase electron impact. Field desorption, fast-atom bombardment, and chemical ionization mass spectrometry have also been successfully applied. 

We report on the further physical and chemical characterization of the new forms of molecular carbon, C ) and C70. Our results demonstrate a high yield of production (14%) under optimized conditions and reveal only and C70 in measurable quantity, in an 8S IS ratio. These two new molecular forms of carbon can be completely separated in analytical amounts by column chromatography on alumina. Comparison among mass spectra obtained by the electron impact, laser desorption, and fast atom bombardment (FAB) methods allows a clear assessment of the composition of the mixed and pure samples, and of the fragmentation and double ionization patterns of the molecules. In addition, spectroscopic analyses are reported for the crude mixture by C NMR and by IR spectroscopy in KBr pellet, and for pure C o and C70 in solution by UV-vis spectroscopy. 

Several physical methods have been employed to ascertain the existence and nature of ICs infrared (IR) absorption spectroscopy nuclear magnetic resonance (NMR) spectroscopy,14 including JH nuclear Overhauser effect (NOE) difference spectroscopy, H 2-D rotating-frame Overhauser effect spectroscopy (2-D ROESY),15 and solid-state 13C cross-polarization/magic angle spinning (CP/MAS) spectroscopy 16 induced circular dichroism (ICD) absorption spectroscopy 17 powder and singlecrystal X-ray diffraction 18 and fast atom bombardment mass spectrometry (FAB MS). 

Because of the complexity of the polyether antibiotics little progress has been made in structure determination by the chemical degradation route. X-ray methods were the techniques most successfully applied for the early structure elucidations. Monensin, X206, lasalocid, lysocellin, and salinomycin were included in nineteen distinct polyether x-ray analyses reported in 1983 (190). Use of mass spectrometry (191), and 1H (192) and 13C nmr (141) are also reviewed. More recently, innovative developments in these latter techniques have resulted in increased applications for structure determinations. For example, heteronuclear multiple bond connectivity (hmbc) and homonudear Hartmann-Hahn spectroscopy were used to solve the structure of portimicin (14) (193). Fast atom bombardment mass spectrometry was used in solving the structures of maduramicin alpha and co-factors (58). 

Moreover, the typical tools of supramolecular chemistry, such as NMR spectrometry, require concentrations usually in excess of 10 " mol/1. and other favorite methods such as mass spectroscopy [fast-atom bombardment (FAB), electrospray ionization (ESI), matrix-assisted laser desorption ionization (MALDI)], and vapor-pressure os-moinetry do not directly provide information about supramolecular behavior in solution. The most favorite method, x-ray analysis, suffers from the limitation posed by the ultimate requirement of being able to grow single crystals. While this is. in numerous instances, possible in the case of pure molecular entities, supramolecules, being mixed molecular objects by nature, are usually difficult to grow in the form of a single crystal. 

HPLC methods previously described (22.24.26.42). The cinnamoyl ester-bearing compounds were detected by uitraviolet (UV) monitoring at 280 nm. Structure elucidation of the purified compounds was carried out by means of infrared (iR) and UV spectrophotometry, proton and carbon-13 nuciear magnetic resonance (NMR) spectroscopy, and electron impact (EI-) and fast-atom bombardment mass spectrometry (FAB-MS). The structures of the two new isolates and three of their derivatives were established on the basis of spectroscopic data and spectrai evidence obtained on comparison with azadirachtin (23). 

Investigation of interfacial effects and interactions between biocompounds and transducer surfaces at the molecular and atomic levels by exploiting new methods of surface analysis (e,g scanning microscopy techniques, fast-atomic-bombardment mass spectrometry, laser-assisted mass spectrometry, time-of-flight secondary ion mass spectrometry, Fourier-transform infrared spectrometry, ellipsometry. X-ray photoelectron spectroscopy, and electron microscopy)... 

Procedures for etherification and esterification of carbohydrates for GLC analysis, advantages and disadvantages of the different methods of hydroxyl and aldehyde group derivatization, columns used for the separation of the various derivatives, detection methods for GLC, mass spectroscopy and fast atom bombardment (FAB) as well as outlines of some strategies for structural analysis of carbohydrates are described, discussed and reviewed in an excellent book on the analyses of carbohydrates by GLC (35). 

It was not possible to use MS for the characterization and identification of chlorophylls and its derivatives until the development of desorption methods (desorption ionization) appropriate for nonvolatile and thermolabile compounds. The mass spectmm of chlorophylls has been obtained using laser desorption [92-94], field desorption [95], plasma desorption [96,97], fast atom bombardment (FAB) [28, 98-101], in-beam electron ionization [102], and electrospray ionization (ESI) [103]. A combination of the techniques of desorption and tandem mass spectroscopy (MS/MS) has also been used for the charactmzation of chlorophylls and derivatives [ 104—107]. The latest research in this field coupled HPLC with MS, using as ionization source FAB [108-110] or atmosphoic pressure chemical ionization (APCI) [111-115]. 

Lattimer and co-workers [30] have applied mass spectroscopy to the determination of antioxidants and antiozonants in rubber vulcanisates. Direct thermal desorption was used with three different ionisation methods (electron impact, Cl, field ionisation (FI)). The vulcanisates were also examined by direct fast atom bombardment mass spectroscopy (FAB-MS) as a means for surface desorption/ionisation. Rubber extracts were examined directly by these four ionisation methods. Of the various vaporisation/ ionisation methods, it appears that FI is the most efficient for identifying organic additives in the rubber vulcanisates. 

See also Biochemical Applications of Mass Spectrometry Biomedical Applications of Atomic Spectroscopy Chromatography-MS, Methods Fast Atom Bombardment Ionization in Mass Spectrometry Isotopic Labelling in Mass Spectrometry. 

About ten years ago the author speculated that between the extremes mentioned above a third set of reaction conditions and a third group of reaction products might exist, namely reaction conditions yielding soluble multicyclic polymers. Such polycondensations yield a complex mixture of reaction products which cannot satisfactorily be characterized by classical spectroscopic methods such as IR-, NMR and NMR spectroscopy. Mass spectrometric methods such as Fast-Atom-Bombardment, and above all, MALDI-TOF mass spectrometry are required, and even these methods do not answer all questions concerning the structure of the reaction products. Hence, a systematic exploration of this new working field was not feasible before the year 2000, i. e. before powerful MALDI-TOF mass spectrometer became commercially available. 

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