Mass fragmentation

Figure 6.34. Adjustment factor for unequal mass fragments (Baker et al. 1983).

Ethoxy, aminochloro, aminoethoxy, and diamino derivatives of the 3-nitronaphthyridines show a more differentiated mass fragmentation. Besides the loss of NO2, HCN, and NO, expulsion of OH, CO, C2H4, and O was observed as well. 

Figure 1.3. Mass spectrum showing a small molecular ion at m/z 137 and lower mass fragment ions.

Table 2. Mass fragments used in identification of components described in this article, used in these experiments were CjH4, CHjCOOH, Oj, and He.

These mass fragments were foimd by our own measmements... 

The position of the methyl group of 25b,c was deduced from high-resolution mass analysis as shown in Figs. 1 and 2. The mass fragmentation pattern of 25b was quite different from that of 25c, thus assuring the differ-... 

Laser microprobe MS (LMMS) can be used for direct analysis of normal-phase HPTLC plates [802,837]. Kubis et al. [802] used polyamide TLC plates polyamide does not interfere with compound identification by the mass spectrum, owing to its low-mass fragment-ions (m/z < 150). LMMS is essentially a surface analysis technique, in which the sample is ablated using a Nd-YAG laser. The UV irradiation desorbs and ionises a microvolume of the sample the positive and negative ions can be analysed by using a ToF mass spectrometer. The main characteristics of TLC-LMMS are indicated in Table 7.84 [838],... 

In Table IV some physical data and spectral characteristics of 6,7-secoberbines are listed. Only methyl corydalate (55) is optically active. Formula 55 presents the spatial structure of this compound, deduced by Nonaka et al. (65) and confirmed by Cushman et al. by both correlation with (+)-mesotetrahydrocorysamine (72) (<5S) and total synthesis (69). It is difficult to find common characteristic features in both the mass and H-NMR spectra of these alkaloids because they differ significantly from each other in their structures. On one hand, corydalic acid methyl ester (55) incorporates a saturated nitrogen heterocycle, while the three aromatic bases (56-58) differ in the character of the side chain nitrogen. For example, in mass fragmentation, ions of the following structures may be ascribed to the most intensive bands in the spectrum of 55 ... 

In the mass spectra of all these substances (4,5,14,15,87,92,94), the molecular ions peaks are present. The base peak at m/z 58, typical for all the seco alkaloids with the N,iV-dimethylaminoethyl chain, corresponding to the CH2=N(CH3)2+ ion is observed. The main mass fragmentation under electron impact seems to involve bond cleavage between C-l and C-9. This can be evidenced by the presence of ions of the 122 and 123 type found in spectra of all compounds except for N-methylhydrastines (98, 99), where the 123 — C02 ion is formed instead. Finally, the carbonyl group absorption... 

The main mass fragmentation of secobenzylisoquinoline alkaloids involves bond cleavage between the two benzylic carbonyls. This process is evidenced by the presence of peaks representing fragment ions at m/z 151, found in spectra of all these bases and attributed to the lower portion of the molecules, and ions at m/z 220,236, and 222, found in spectra of 159,160, and 161, respectively, formed from the upper part of the compounds. Similarly, as in the mass spectra of other secoisoquinoline alkaloids incorporating the amino-ethyl substituent, the [H2C=N(CH3)2]+ ion at mjz 58 is the base peak. 

It should be pointed out that FAB, MALDI, and ESI can be used to provide ions for peptide mass maps or for microsequencing and that any kind of ion analyzer can support searches based only on molecular masses. Fragment or sequence ions are provided by instruments that can both select precursor ions and record their fragmentation. Such mass spectrometers include ion traps, Fourier transform ion cyclotron resonance, tandem quadrupole, tandem magnetic sector, several configurations of time-of-flight (TOF) analyzers, and hybrid systems such as quadrupole-TOF and ion trap-TOF analyzers. 

Table I gives the mass fragments observed by electron impact ionization at each one of these three excitation energies. The results confirm the fact that both metal-metal and metal-CO cleavage occurs in the low energy band, while excitation into higher excited states enhances the metal-CO channel at the expense of the Mn-Mn bond homolysis.

Table I. Mass Fragments Observed by Electron Impact Ionization as a Function of Photolysis Excitation Energy...

The mass spectrum of miconazole nitrate was obtained using a Shimadzu PQ-5000 mass spectrometer. The parent ion was collided with helium as the carrier gas. Figure 15 shows the detailed mass fragmentation pattern and Table 5 shows the mass fragmentation pattern of the drug substance. Clarke reported the presence of the following principal peaks at mlz = 159, 161, 81, 335, 333, 163, 337, and 205 [2],... 

Figure 9 shows the detected mass fragmentation pattern of niclosamide. The major peaks in the spectrum occur at m/z 326, 291, 172, 156, 155, 154, 144, 142,... 

The mass spectrum of (/i/.)-penicillamine was obtained utilizing a Shimadzu PQ 0-5000 mass spectrometer. The detailed mass fragmentation pattern is shown in Fig. 7, where a base peak was observed at mlz 75. The proposed mass fragmentation pattern of (/i/.)-penicillamine is summarized in Table 5. It is worth mentioning that the drug did not show a molecular ion peak. A proposed scheme of the MS fragmentation pattern of (z>z.)-penicillamine is shown in Fig. 8. 

Figure 3.15 Significant mass fragments in PCA analysis of DE MS data of the examined triterpenoid substances and the value of their loadings in calculating PCI and PC2...

ToF-SIMS mass spectra are generally obtained for m/z ratio from 1 to 1000 or 2000. However, due to a high fragmentation process, ToF-SIMS mass spectra are generally very complex and the fragmentation/ionization processes are very different compared with other mass spectro-metric techniques. The main peaks are generally low mass fragments (m/z < 100). 

In the multistage approach, ToF-SIMS plays an important role and is first used to detect the presence of proteins in museum objects. Indeed, if blood is present in such a state of conservation that it can be recognized through chemical composition, proteins must be present. For this purpose, as described previously, low mass fragments are studied. Since samples are very complex and in order to ensure identification, two-dimensional images of all protein fragments are drawn and compared. Correlation between the different images confirms the presence of proteins. 

Isotope dilution gas chromatography-mass spectrometry has also been used for the determination of ppb of total chromium in seawater [181-183]. The samples were reduced to ensure Cr111 and then extracted and concentrated as tris (l,l,l-trifluoro-2,4-pentanediono) chromium (III) [(Cr(tfa)3>] into hexane. The Cr(tfa)2 mass fragments were monitored into a selected ion monitoring (SIM) mode. 

In this method, chromium is extracted and preconcentrated from seawater with trifluoroacetylacetone [H(tfa)] which complexes with trivalent but not hexavalent chromium. Chromium reacts with trifluoroacetylacetone in a 1 3 ratio to form an octahedral complex, Cr(tfa)3. The isotopic abundance of its most abundant mass fragment, Cr(tfa)2 was monitored by a quadrupole mass spectrometer. 

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