Field desorption mass spectra

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.

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).

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 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. 

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. 

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. 

Field desorption mass spectrum of poly(styrene) 12500. (Reprinted from Ref. 14 with permission... 

Arginine is known to be a delicate thermosensitive sample. Mass spectra of the intact molecule neither upon electron impact nor upon chemical ionization are known, since this molecule undergoes a neutral decompositon reaction upon heating. A field desorption mass spectrum of the protonated molecule has been measured/26/. 

A blue pigment from extracts of E. incanum was oxidised to incaflavin (534) merely on standing in aqueous solution. This observation, together with the similarity between the electronic spectrum of this blue substance and that of the bacterial pigment indigoidin (535) 417), prompted the proposal that the blue fungal compound possessed the dimeric structure (536). This suggestion was supported by the presence of a molecular ion of appropriate mass in the field desorption mass spectrum. 

Field desorption mass spectrum quasi-molecular ion at mie = 368 and a more intense peak at mIe = 331 (M—HCl). 

Degradation products from base treatment of cefaclor have not been isolated for characterization. A piperazine-2,5-dione (133) was obtained from refluxing the p-nitrobenzyl ester of cefaclor (132) in benzene. Cephalexin p-nitrobenzyl ester (130) in a parallel experiment had been shown to give 131. Quite unexpectedly, this degradation product of cefaclor contained no chlorine in elemental analysis the field desorption mass spectrum suggested the loss of HCl. The structure for 133 was derived from proton and C-NMR analyses. 

Pyrazofurin was obtained courtesy of Eli Lilly Co., Indianapolis, Ind. (Lot y/f CT-2940-4B). Each ampoule contained 300 mg PF as lyophylized powder and was reconstituted with 10 ml of sterile 0.15 M NaCl prior to use the vials were stored in a refrigerator. Pyrazofurin 5 -monophosphate (PFP) was obtained courtesy of Eli Lilly Co., Indianapolis, Inc. PFP was synthesized by the 5 --phosphorylation of a 2 ,3isopropylidene derivative of PF, followed by removal of the ketal protecting group (5). The field desorption mass spectrum of PFP revealed a strong signal at m/e 340, corresponding to the protonated molecular ion (12). 

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