Positive-ion mass spectra

Dienes and polyenes show a pronounced molecular ion in the mass spectra and hence the molecular weight of polyenes can be determined by positive ion mass spectra. The easy removal of a 7r-electron from a diene is usually the reason for the distinct M +. The mass spectral investigation of conjugated polyenes is somewhat similar to that of aromatic structures, due to the high stability of the rearranged ions formed after the... 

Fig. 2.30. Total ion current chromatogram of alga Spirulina Platensis algae sample by LC-TurbolSP-MS and positive-ion mass spectra of the carotenoids identified 1 = zeaxanthin 2 = /Tcryptoxanthin 3 = /1-carotene. Reprinted with permission from M. Careri et al. [69].

FIGURE 4 ESI positive ion mass spectra of angiotensin I with charge states of + I, +2, +3, and +4 (courtesy of Thermo Finnigan). 

FIGURE 11.71 Typical laser ionization positive ion mass spectra of single particles in rural Colorado (adapted from Murphy and Thomson, f997a,b). 

The coupling of HPLC to a mass spectrometer (MS) has provided for the ultimate in detection systems in terms of sensitivity and versatility. Betourski and Ballard (227) have used the techniques of thermospray TSP-LC-MS and tandem LC-MS-MS to obtain positive-ion mass spectra of two cationic dyes, Basic red 14 and Basic orange 14. According to Yinon et al. (228), TSP-LC-MS has been found to be a suitable technique for the analysis of dyes. It is sensitive and specific, and the ionization process is soft. One of the drawbacks, however, is that one obtains... 

The 60% methanol sep-pak fractions from the mimosa foliage and sericea extracts were analyzed by LC/MS. The mimosa foliage fractionhad nearly the same profiles by both LC/MS (Fig. 4B) and HPLC (Fig. 4A), as indicated by the three major peaks. The LC/MS profile showed that the mimosa foliage fraction had major peaks at 42.5 (significant ions at m/z 303 and 633), 49.0 (m/z 303 and 487), and 53.5 (m/z 303 and 471), min. The molecular weights of compounds were inferred from the positive-ion mass spectra (results not shown). On the other hand, the chromatograms for the sericea extracts (Fig. 5A, 5B) are quite different. The LC/MS profile for sericea in Fig. 5B shows major peaks at 47.0 (major ions at m/z 433 and 545) and 48.5 (m/z 517 only) min. 

Fig. 9 Positive ion mass spectra from an APCI LC/MS analysis of an elastomer solvent extract (note chromatograms in Fig. 8).

B.M. Kolakowski, J.S. Grosser , L. Ramaley, Studies on the positive-ion mass spectra from APCI of gases and solvents used in LC and direct liquid injection, J. Am. Soc. Mass Spectrom., 15 (2004) 311. 

Thermosprav Operation. Figures 2 and 3 show the thermospray positive ion mass spectra of HARMONY and LONDAX. The spectra contain three to four structurally informative ions. For quantitation at the method detection level in each case, we selected the most intense ions. 

Figure 55-10 Electron impact positive ion mass spectra of isomeric acylglycines detected by GC/MS analysis of organic acid trimethyisily (IMS) derivatives. A, 3-liethylcrotonylglycine monO TMS ester (leucine metabolism). B, Tiglylglycine mono-TMS ester (isoleucine metabolism). As their retention times are relatively close in most chromatographic systems, proper differentiation betv een the two compounds is best achieved by evaluation of the fragment ion at m/z 82 (arrow) which is prominent in the spectrum of 3-methylcrotonylglydne but not tigiylgiycine.

The positive ion mass spectra of pyridine Af -unsubstituted N-imines, generated within the ion source by pyrolysis of the corresponding hydrochlorides, have been investigated.133 The mass spectrum of pyridine AMmine contains peaks attributable to the loss of 15 (NH) and 16 (NH2) mass units from the molecular ion in a ratio of approximately 2.5 1, whereas introduction of a methyl group at the 2-position of the pyridine ring causes a significant change in the intensity ratio of the [M — NH]+ and [M — NH2] + ( 1 2.5). This can be attributed to the operation of a so-called ortho effect, as in the case of 2-alkylated pyridine N-oxides. 

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