Field desorption cationization

Mass Spectrometry. Field desorption mass spectrometry has been used to analy2e PPO (179). Average molecular weight parameters (M and could be determined using either protonated (MH + ) or cation attachment (MNa + ) ions. Good agreement was found between fdms and data supphed by the manufacturer, usually less than 5% difference in all cases up to about 3000 amu. Laser desorption Fourier transform mass spectrometry was used to measure PPG ion and it was claimed that ions up to m/2 9700 (PEG) can be analy2ed by this method (180). 

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). 

Mass spectrometry (MS) in its various forms, and with various procedures for vaporization and ionization, contributes to the identification and characterization of complex species by their isotopomer pattern of the intact ions (usually cation) and by their fragmentation pattern. Upon ionization by the rough electron impact (El) the molecular peak often does not appear, in contrast to the more gentle field desorption (FD) or fast-atom bombardment (FAB) techniques. An even more gentle way is provided by the electrospray (ES) method, which allows all ionic species (optionally cationic or anionic) present in solution to be detected. Descriptions of ESMS and its application to selected problems are published 45-47 also a representative application of this method in a study of phosphine-mercury complexes in solution is reported.48... 

Guo, X. Fokkens, R.H. Peeters, H.J.W. Nibbering, N.M.M. de Koster, C.G. Multiple Cationization of Polyethylene Glycols in Field Desorption Mass Spectrometry a New Approach to Extend the Mass Scale on Sector Mass Spectrometers. Rapid Commun. Mass Spectrom. 1999,13, 2223-2226. 

The precursor model of FAB applies well to ionic analytes and samples that are easily converted to ionic species within the liquid matrix, e.g., by protonation or deprotonation or due to cationization. Those preformed ions would simply have to be desorbed into the gas phase (Fig. 9.6). The promoting effect of decreasing pH (added acid) on [M+H] ion yield of porphyrins and other analytes supports the precursor ion model. [55,56] The relative intensities of [Mh-H] ions in FAB spectra of aliphatic amine mixtures also do not depend on the partial pressure of the amines in the gas phase, but are sensitive on the acidity of the matrix. [57] Furthermore, incomplete desolvation of preformed ions nicely explains the observation of matrix (Ma) adducts such as [M+Ma+H] ions. The precursor model bears some similarities to ion evaporation in field desorption (Chap. 8.5.1). 

Field-desorption mass spectrometry (FDMS), where no evaporation prior to ionization is required, has been successfully used in the analysis of in volatile phosphonium salts113, although a direct thermal process gave similar spectra114. In the case where the FD spectra are complex, a chemical ionization technique may give wider applicability115. The cation is the base peak for monophosphonium salts when the [2M + anion]+ cationic species is the one for bisphosphonium compounds. 

Ionization Methods/Processes. The recent development of several new ionization methods in mass spectrometry has significantly improved the capability for the analysis of nonvolatile and thermally labile molecules [18-23]. Several of these methods (e.g., field desorption (FD), Californiun-252 plasma desorption (PD), fast heavy ion induced desorption (FHIID), laser-desorption (LD), SIMS, and fast atom bombardment (FAB) or liquid SIMS) desorb and ionize molecules directly from the solid state, thereby reducing the chance of thermal degradation. Although these methods employ fundamentally different excitation sources, similarities in their mass spectra, such as, the appearance of protonated, deprotonated, and/or cationized molecular ions, suggest a related ionization process. 

Guo, X., Fokkens, R. H., Peeters, H. J. W., Nibbering, N. M. M., and de Koster, C. G. (1999). Multiple cationization of polyethylene glycols in field desorption mass spectrometry A new approach to extend the mass scale on sector mass spectrometers. Rapid Commun. Mass Spectrom. 13, 2223-2226. 

Schulten (110, 111) has used laser-assisted field desorption mass spectrometry to study some inorganic and organometallic systems. This method is intermediate between LAMMA and simple FD. Metal cations predominate from inorganic salts. The technique also showed clusters of the type reported from both FAB and SIMS studies. By carefully controlling the laser, a chlorophyll molecular ion could be obtained as well as fragments relating to its structure. 

Field desorption mass spectrometry has been successfully applied to mono- and bis-alkyl- and -alkenyl-triphenylphosphonium salts (187). The phosphonium cation gave rise to the base peaks. ... 

Applications of FAB have been succesfully performed in the characterization of a wide range of compounds (dyes, surfactants, polymers...) but little attention has been devoted to the capabilities of this technique to solve environmental concerns, such as organic pollutants identification in water. The widespread use of surfactants in the environment has required the emplo yment of both sensitive and specific methods for their determination at trace levels. GC/MS and HPLC procedures has been used for the determination of anionic (LAB s) and non ionic surfactants (NPEO) in water (1-4). Levsen et al (5) identified cationic and anionic sirrfactants in surface water by combined field desorption/ collisionally activated decomposition mass spectrometry (FD/CAD), whereas FAB mass spectrometry has been used for the characterization of pine industrial surfactants (6-8). 

The MS of compound 178 showed a molecular peak with m/z 661 and fragmentation peaks typical of the alkyl groups. The peak corresponding to cation 75 (item N-4 of Table 2) is the parent peak of the field desorption MS of its salts. The peak for [Au(S2C2BioHio)2], corresponding to the carborane complex anion 83 (entry S-4 of... 

Puzo G, Tissie G, Lacave C, Aurelle H, Prome JC. Structural determination of cord factor from a Corynebacterium diphtheriae strain by a combination of mass spectral ionization methods field desorption cesium cationization and electron impact mass spectrometry studies. Biomed Mass Spectrom. 1978 5 699-703. 

Deutsch J, Gilon C, Chorev M. Field desorption mass speetrometry. II. Potassium cation-ization field desorption mass speetrometry of some penta- and hexapeptides derived from substanee P. Int J Pept Protein Res. 1981 18 203-7. 

Field desorption - collision induced dissociation mass spectra of seven disaccharides, involving alkali metal-cationized... 

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