MIKE/CAD spectra

MIKE/CAD spectra, in addition to their interest for structural determinations, are... 

Indeed, it is possible to obtain MIKE/CAD spectra of isobaric ions [154a,b]. For example, after elimination of 43 amu fragment, cyclohexanone leads within the... 

Figure 28. MIKE/CAD spectra of various protonated molecules of 1,4-cyclohexane ether (a), cyclohexanone (b) and cyclohexane oxide (c) produced under tC4,H9/CI [152].

The MIKE/CAD spectra of each ion are sufficiently different so that we may admit the separation of these ions, as shown by the non-existence of ions arising from the loss of 4,5 or 6 hydrogen atoms, as well as that of the m/z 39 ion in the MIKE/CAD spectrum of the isobaric ion CaHjO]". Inversely, the very low intensity of the m/z 41 peak in the MIKE/CAD spectrum of the C4H7] ion is proof of the good separation of these isobaric ions Fig. 29). 

Figure 29. MIKE/CAD spectra of C3H3O and QH, isobaric ions [m/z 55) produced from cyclohexanone under El conditions [154a].

Figure 34. MIKE/CAD spectra showing positively and negatively charged products both arising from the [M-H] anion of p-chlorobenzoic acid [164].

This program contains all the possibilities of rapid and sensitive analysis of metastable spectra, regardless of the mode employed, with averages of MIKE (or MIKE/CAD) spectra. 

In order to obtain more intense molecular peaks, Levsen and co-workers [197] chose the field ionization (FI) method, much softer than electron impact ionization, and utilized collision-induced decompositions rather than unimolecular decompositions. They were thus able to identify estrone (m/z 270) and progesterone (m/z 314) in an artificial mixture (Table 13). The FI/MIKE/CAD spectra of the molecular ions are... 

Analysis of steroid mixtures using MIKE/CAD spectra under FI conditions (FI/CAD spectra) [197]... 

As stated above, the analysis of certain of these peaks in MIKE/CAD spectra is very useful for determining the structure of molecules [209], especially for demonstrating the presence of unsaturations, of cyclopropenes on side chains, etc. (Table 18). 

In practice, the situation is not as simple as that, since MIKE/CAD spectra have a low resolution, leading to a few difficulties when isomers (or fragment) ions are present (or compounds with new structures) and when performing certain identifications. Nevertheless, the objective can be achieved, as shown by this review [209]. 

Cooks and co-workers [210] identified each individual protonated molecule MH from various steroids contained in biological matrices by studying their MIKE/CAD spectra. Collisions are necessary in this ionization mode in order to increase the number of characteristic daughter ions. In certain cases, however, spontaneous decompositions are sufficiently numerous, especially in the first FFR. 

The study of MIKE/CAD spectra of protonated molecules of various compounds characterized by a A -3-keto system (such as testosterone, corticosterone, norgesterel, etc.) leads to the demonstration of peaks with non-negligible intensities at m/z 147, 135, 123, 109 and 97, with ratios that are very close. Certain fragment ions, including the [MH-CH3OH] ion, produced from hydroxycortisone (with the same A -3-keto sequence) also generate the same characteristic ions, and thus a certain amount of caution is required. 

Protonated molecules from steroids with a phenolic A ring may be characterized similarly by the presence of intense peaks at m/z 157, 135 and 107, as well as [MH-H20] in their MIKE/CAD spectra. 

Protonated isomeric molecules, such as testosterone and dehydroepiandrosterone, are characterized in the MIKE/CAD spectra by peak widths, but also by intensities, which vary as a function of collision gas pressure. 

Thus, there is no difficulty in determining the sequence of the AcN-Gly-Ala-Leu-OCH3 peptide. In a more thorough report of this work [218], the authors presented all the aspects offered by the use of MIKE/CAD spectra, including the study of a mixture of oligopeptides with sufficient sensitivity the decreased possibility... 

The major disadvantage of MIKE/CAD spectra, however, is related to the widening of metastable peaks, which reduces energy resolution. 

All three include the C4H9 radical and can decompose spontaneously (or collision-ally) to eliminate either the primary (-CH2-CH(CH3)2) or secondary (-CH(CH3)-CH2-CH3) isobutyl radical. Consequently, several differences are observed in the MIKE/CAD spectra. However, the greatest differences appear in the decomposition spectra of m/z 103 ion (Table 22), which is consistently present when the polypeptide has an He or Leu residue in terminal position. 

MIKE and MIKE/CAD spectra of ion (CD3NH =CH(C4H,))m/z 103 produced from peptides where the Leu (or lieu) group is present in various positions [218]... 

It is to be borne in mind that it is not always necessary to perform MIKE/CAD spectra, since occasionally spontaneous decompositions are sufficient. 

These MIKE/CAD spectra are in general characterized by the presence of an m/z 18 ion, which may have originated from either or NH4. The presence of a non-... 

If collision reactions (MIKE/CAD spectra) on this ion are insufficient for the generation of fragment ions, it is then preferable to perform these reactions on the [M-H] ions formed during the reversed charge of [M-H] . 

Figure 88. Partial MIKE/CAD spectra of (M + NH4) ions produced from a- and -cellobiose, a- and -maltose, a- and -isomaltose, ot- and -gentiobiose (in CI/NH4) [236].

In addition to distinguishing the disaccharide linkage bond in various stereomeric species, measurements of collisional-induced decompositions (as MIKE/CAD spectra) also enable one to differentiate the diastereomeric disaccharides themselves, providing that protonated molecular ions are not used [236]. 

Figure 89. Partial MIKE/CAD spectra [M + HN(CH3)j] ions produced from

The MIKE/CAD spectra of the MH" peak of both these compounds are characterized by the presence of the same very intense ion at m/z 182, corresponding to the loss of CsHsCOOH in one case and CgHj-CH =CH-COOH in the other. 

Figure 96. MIKE/CAD spectra of miz 134 ions, differentiating between tetrahydroquinoline and isoquinoline by the intensities of double charge ions [158,246],...

Figure 97. MIKE/CAD spectra of m/z 174 ions. These isomer ions are produced from various precursors tetramethylthiazolidine (a), penicillin (b) and dehydrocephalosporin (c) [248].

Figure 98. MIKE/CAD spectra of m/z 176 ion (natural 8 isotope of m/z 174 ion) (upper) and m/z 174 from penicillin [248].

Figure 101, MIKE/CAD spectra of mjz 126 ion from salmon DNA (lower) compared to mjz 126 ion produced from authentic 5-methyldeoxycytidine sample (upper) [251].

Figure 102, MIKE/CAD spectra of isomer structure m/z 150 ions and presence of ions a, b, c and d formed from impurities in the MIKE/CAD spectrum of m/z 150 ion from salmon sperm DNA (the artefacts are denoted by asterisks in the latter spectrum) [251],...

High-resolution measurements indicate that each peak, at m/z 32,41,68,82 and 98, corresponds to radical ions. At 14 eV it is probable that they are molecular ions. The comparison of the MIKE/CAD spectra of these various ions and those of authentic compounds of the same composition led to the unambiguous identification of these ions (Table 28). 

MIKE/CAD spectra of m/z 98 ions (CjH Oj ) formed by pyrolysis of DNA and other m/z 98 ions produced from a-angelica lactone and furfuryl alcohol [253]... 

The superposition of several pure MIKE/CAD spectra on the same spectrum may indeed cloud the issue . Nevertheless, we believe that by changing either collision gas pressure or type, it is possible to obtain sufficient information to resolve the ambiguities. Those which remain are due (relatively rarely) to the partial isomerization of molecular ions and fragment ions which are most often encountered. In the latter case, the examination of the MIKE/CAD spectra of other fragment ions belonging to the conventional mass spectrum may be useful for determining these structures. 

Considerable experimental difficulties often arise when non-volatile and thermo-labile molecules are analyzed. The exploitation of MIKE (and MIKE/CAD) spectra of these high-molecular-mass ions is rendered delicate by poor energy resolution. 

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