Field desorption spectrum

Figure 2()-6c is a field desorption spectrum for glutamic acid. Ii is even simpler lhan the spectrum from field ioni/aiion and consists of only the proionaied molecular ion peak at m/z 148 and an isotope peak at m/z - 149. 

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). 

Figure 6.21 Field desorption mass spectrum of the rubber compound (acetone extract analysis) of Table 6.36. After Lattimer et al. [229]. Reprinted with permission from Rubber Chemistry and Technology. Copyright (1990), Rubber Division, American Chemical Society, Inc.

An electron impact mass spectrum of calcium leuco-vorin has not been obtained because the compound is not sufficiently volatile. It would be difficult to isolate the free acid without first dehydrating the compound. Due to its ionic nature, calcium leucovorin will not dissolve in common silylating reagents. Field desorption, another mass spectral technique, generally lends itself more to compounds like leucovorin. Indeed, this technique has been applied successfully to methotrexate and other folic acid analogs.1 ... 

Fig. 1.3. Three representations of the molecular ion signal in the field desorption mass spectrum (Chap. 8) of tetrapentacontane, C54H110 (a) profile spectrum, (b) bar graph representation, and (c) tabular listing.

Fig. 6.42. El mass spectrum of tetrabutylammonium iodide. The intensity scale is 20fold above m/z 220, i.e., disregarding the peaks at m/z 127 and 128 this spectrum is very similar to the mass spectmm of pure tributylamine (Eig. 6.43b for the field desorption mass spectrum cf. Chap. 8.5.3).

Fig. 2.19 ( ) Time-of-flight spectrum in photon stimulated field desorption of water using synchrotron radiation, obtained by Jaenike et al.m...

The simplicity of FD spectra obtained at low emitter currents made possible the analysis of complex mixtures of glycolipids to obtain information about molecular weight distributions. Figure 8 shows the field desorptive mass spectrum obtained for a mixture... 

Figure 6. Field desorption mass spectrum of sphingenine, recorded at 20 ma...

Figure 7. Field desorption mass spectra recorded at 22—23 ma for a biphenyl carbonyl derivative of psychosine and a biphenyl carbonyl derivative of a new compound isolated from human brain tissue. Structure indicated for the unknown was assigned on the basis of this spectrum and chemical evidence relating the unknown to psychosine. Both samples were purified by HPLC prior to FDMS.

Figure 8. Field desorption mass spectrum obtained at 22 ma for a mixture of cerebrosides from bovine brain. Assignments of MH are discussed in the text and...

Figure 11. Field desorption mass spectrum of sphingomyelin obtained at high emitter current (28 ma) and therefore dominated by peaks that correspond to transfer of choline (mass 104) to the three major molecular species present n = 16, MW 730 n = 22.1, MW 812 and n = 22, MW 814. The (M + choline) adducts are observed at m/e 834, 916, and 918, respectively. For the higher MW compounds, the fragment at m/e 548 when n = 16 occurs at m/e 630 and 632.

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. 

Figure 143. Distribution of fatty acid methyl esters (FAME), monoacylglycerols (MG), and diacylglycerols (DG) in a liquid injection field desorption ionization (LIFDI) mass spectrum of biodiesel (Schlichting et al., unpublished).

The field desorption mass spectrum of cimetidine base and a table of the fragmentation peaks are presented in Figure 7 and tabulated in Table 3. 

Field Desorption Mass Spectrum of Cimetidine. Peak Intensity Data. 

Moxalactam disodium can yield a mass spectrum when run in the field desorption mode. The major ions for moxalactam disodium are at m/z of 116 and 130. These are attributed to... 

From the field desorption mass spectra of standard samples, a table for identification of poly(oxyethylene) alkylphenyl ethers and determination of the degree of polymerisation of ethylene oxide was constructed as shown in Table 6.1 n is the number of alkyl carbon atoms and m is the degree of polymerisation of ethylene oxide. When the field desorption mass spectrum having a peak pattern with the difference of 44m/z was obtained such as the peaks at 484, 528, 572, 616 and 660m/z, Table 6.1 would show that those peaks are due to poly(oxyethylene) nonylphenyl ethers with the degree of polymerisation of 6-10 of ethylene oxide. Table 6.2 also shows the identification of poly(oxyethylene) dialkylphenyl ethers and determination of the degree of polymerisation of ethylene oxide based on calculations of the molecular weight. 

A different, but no less severe problem, is encountered with the analysis of unknown biological substances by field desorption, laser desorption, and/or laser assisted field desorption mass spectrometry. A priori, it is not known at what point in time a component of interest is desorbed. This makes it difficult, if not impossible to time a scan or several scans in such a way that a representative spectrum is obtained. Again the answer to the problem is found by integrating the ion output over the entire sample or repeatedly over portions of the sample profile as it emerges from the ion source. 

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