MS, field desorption

With FAB, TOP, MALDI, ESI-MS, field desorption (FD) MS and GC-MS technique the analytical capabilities for non-ionic gemini surfactants were compared [157]. Parees et al. reported on the analysis of a series of oligomeric ethoxylated surfactants of this type which showed an improved surface activity. Even an antibacterial lipopeptide biosurfactant, lichenysin A, cultured and isolated, was analysed by EAB-MS and EAB-MS/MS, ESI-MS and various other methods [158]. The compound was characterised and the lipid moiety contained a mixture of 14 linear and branched P-hydroxy fatty acids from C12 to C17. 

PND was shown to be 10 to 50 times more sensitive than FID (Wink et al. 1982). The other detection method commonly used to obtain further information on the chemical structures was EI-MS. However, even GC-MS data are not always sufficient for the identification of quinolizidine alkaloids, since structural isomers such as tetrahydrorhombifoline and N-methyl-angustifoline were found to have the same retention time and very similar mass spectra but could be distinguished by TLC (thin-layer chromatography) (Balandrin and Kinghorn 1981). From some esters of hydroxylupanine it was not possible to detect the molecular ion (Wink et al. 1982). FD-MS (field desorption) was performed directly on the alkaloid extract to detect the molecular ions of the various bases in the mixture. The identity of the compounds was further confirmed by comparison of their retention indices with the ones of authentic samples. More recently, also CI-MS (isobutane or... 

Of the many analytical techniques now available to the lipid chemist, mass spectrometry (MS), is probably the one that has experienced the fastest growth in the last two decades. This is due both to the development of new techniques (gas and liquid chromatography combined with MS, soft-ionization MS, field desorption MS, atmospheric pressure MS etc.) and to the refinement of more traditional methods and their successful application to very complex problems, e.g. the elucidation of glycolipid structure, or the study of structures in lipid mixtures. Much progress has been made since the pioneering work of Ryhage and Stenhagen (1963) on fatty acid methyl esters. 

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). 

Recent attention has focused on MS for the direct analysis of polymer extracts, using soft ionisation sources to provide enhanced molecular ion signals and less fragment ions, thereby facilitating spectral interpretation. The direct MS analysis of polymer extracts has been accomplished using fast atom bombardment (FAB) [97,98], laser desorption (LD) [97,99], field desorption (FD) [100] and chemical ionisation (Cl) [100]. 

FD-MS, FDMS Field desorption mass spectrometry GCO Gas chromatography-olfactometry... 

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... 

The introduction of soft ionization techniques, such as plasma desorption (PD),[1] field desorption (FD)[2] and fast atom bombardment (FAB),[3] marked the beginning of a new era for MS. In fact, they allowed MS to extend its applications to wide classes of nonvolatile, polar, thermally unstable and high molecular weight analytes. This opened up new horizons for MS in many unexpected fields, such as biology, biomedicine and biotechnology, in which this methodology had not previously found any possible application. 

Over the years, a lot of desorption ionization techniques have been introduced to MS, such as plasma desorption, field desorption, laser desorption, secondary ion mass spectrometry, fast atom bombardment, matrix assisted laser desorption and desorption electrospray ionization. Most of them are actually no longer used. In the following paragraphs, both matrix assisted laser desorption (MALDI) and desorption electrospray ionization (DESI) will be discussed. 

See also Table 8 for X-ray crystallographic analysis. CFDMS = field desorption MS. 

Field desorption MS proved to be the most effective MS technique for the detection and determination of bis(quatemary ammonium) molecules, such as the antibiotic drug ethonium (21 6)431,432. 

Hunt, D.F. Shabanowitz, J. Botz, F.K. CI-MS of Salts and Thermally Labile Organics With Field Desorption Emitters as Solids Probes. Anal. Chem. 1977, 49, 1160-1163. 

Lattimer, R.P. Field ionization (Fl-MS) and Field Desorption (FD-MS), in Mass Spectrometry of Polymers, Montaudo, G. Lattimer, R.P., editors CRC Press Boca Raton, 2001 pp. 237-268. 

Frauenkron, M. Berkessel, A. Gross, J.H. Analysis of Ruthenium Carbonyl-Porphyrin Complexes a Comparison of Matrix-Assisted Laser Desorp-tion/Tonization Time-of-Hight, FAB and Field Desorption-MS. Eur. Mass. Spectrom. 1997,5,427-438. 

The purpose of the MS techniques is to detect charged molecular ions and fragments separated according to their molecular masses. Most flavonoid glycosides are polar, nonvolatile, and often thermally labile. Conventional MS ionization methods like electron impact (El) and chemical ionization (Cl) have not been suitable for MS analyses of these compounds because they require the flavonoid to be in the gas phase for ionization. To increase volatility, derivatization of the flavonoids may be performed. However, derivatization often leads to difficulties with respect to interpretation of the fragmentation patterns. Analysis of flavonoid glycosides without derivatization became possible with the introduction of desorption ionization techniques. Field desorption, which was the first technique employed for the direct analysis of polar flavonoid glycosides, has provided molecular mass data and little structural information. The technique has, however, been described as notorious for the transient... 

Successful mass spectrometry of concave acids and bases was possible in most cases by El, 70 eV. But in some cases, only other MS techniques gave molecular peaks field desorption [12a] FAB-MS (m-nitrobenzyl alcohol) [27b] El, 12eV [28]... 

HPLC and fluorimetric detection, identification with field-desorption MS. 

A convincing body of experimental, information, now available in the literature, serves as confirmation for the possibility to desorb molecular ions out of the condensed phase even for organic molecules which are generally considered nonvolatile and/or fragile and do therefore not lend themselves to classical mass spectrometric analysis. Here the laser-MS competes with techniques such as static SIMS or FABMS, plasma- and field-desorption. 

Cycleanine JV-oxide (111), [oi] 5 -7.6° (c 0.38, MeOH), is apparently not an artifact since it occurs [with cycleanine (112)] even in fresh extracts of Synclisia scabrida Miers (Menispermaceae). The electron impact mass spectrum (EI-MS) is similar to that of cycleanine (m/e 622), but the field desorption mass spectrum (FD-MS) shows principal m/e 638. The H NMR is comparable to that of 112, except for an AT-methyl shifted to 8 3.32. Reduction of 111 with H2S03 gave 112 also, 111 was the less polar product of reaction of cycleanine with H202 (65). Because of symmetry, only two monoxides are possible, but the stereochemistry of the oxidized nitrogen of 111 was not determined. 

Chemical ionization (CI)-MS can be used to study alkaloids that are not amenable to examination by electron impact (EI)-MS. For example, the quaternary alkaloid thalirabine (Section II,C, 123), undergoes fragmentation under the conditions of EI-MS and does not show a parent ion however, the CI-MS shows a double Hofmann elimination product which retains the skeletal atoms (32). Field desorption (FD)-MS has similar utility, as in the case of cycleanine IV-oxide (Section II,C,17) for which FD-MS shows the parent ion not detectable by EI-MS (65). Desorption/CIMS (D/CIMS) was used on dihydrosecocephar-anthine (Sec. H,C,30) and related bases (80,292a). 

Analytical pyrolysis is defined as the characterization of a material or a chemical process by the instrumental analysis of its pyrolysis products (Ericsson and Lattimer, 1989). The most important analytical pyrolysis methods widely applied to environmental samples are Curie-point (flash) pyrolysis combined with electron impact (El) ionization gas chromatography/mass spectrometry (Cp Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS). In contrast to the fragmenting El ionization, soft ionization methods, such as field ionization (FI) and field desorption (FD) each in combination with MS, result in the formation of molecule ions either without, or with only very low, fragmentation (Lehmann and Schulten, 1976 Schulten, 1987 Schulten and Leinweber, 1996 Schulten et al., 1998). The molecule ions are potentially similar to the original sample, which makes these methods particularly suitable to the investigation of complex environmental samples of unknown composition. 

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