Common fragmentation ions

Underivatized diamines are difficult to identify by their mass spectra alone because of the low abundance of the molecular ion (<3%). However, M - 17 is a common fragment ion. j3-cleavage is prominent in diamines. 

Table A4.4 Masses of some possible compositions of common fragment ions 1438...

There are many other isomers in MS/MS analysis, such as several acyl-camitines that share the same mass, such as many of the hydroxyacylcami-tines and dicarboxylic acid acylcamitines. In addition, interfering products may, at times, share a common fragment ion or neutral loss and as a result will be detected in a profile. No method, however, is perfectly selective and a physician reviewing results from a newborn screen, whether analyzed using an immunoassay or MS, should be aware of the fact that in some cases, similar mass compounds may lead to potential sources of error. 

TABLE 3 Common Fragment Ions or Neutral Losses of Different Lipid Groups in ESI-MS/MS ... 

Fig. 13.7 The common fragment ion indicative of the spiroquinazoline alkaloids isolated from a Murraya paniculata endophyte, Eupenicillium spp.

Hard ionisation techniques commonly fragment molecular ions, leading to the loss of neutral species and the formation of fragmentation ions. Some common species lost in mass spectra, and possible chemical inferences that can be drawn from this information, are shown in Table 13.10. In contrast, examples of common fragment ions that are formed are listed in Table 13.11. 

There are two types of mass spectroscopy rules that concern (1) common fragment ions and (2) common fragments lost. Both of these rules can be defined in the same type of data structure. The components of the data structure are ... 

Mass spectra of arsilidene complexes, [Cp Mn(CO)2]2AsR, 17-24 (Table 3), contain molecular ion peaks. The most common fragment ions correspond to elimination of 2CO, R and Cp Mn(CO)2. The abundances of these ions depend strongly on the R substituent at the As atom (Table 4). Substituents R such as F, I, OCS, NCS and N3 are easily eliminated directly from the molecular ion. Loss of Ph, however, occurs only after elimination of all carbonyl ligands, and R = H, R = c-Hex are not lost at all. Only compounds with R = Ph, H and c-Hex have mass spectra which display peaks corresponding to (M—2CO) and (M-4CO) ". The formation of (M — R — nCO) (n = 2,4) ions is characteristic of complexes containing R = I, OCS, NCS and N3. The complex having R = F is intermedi-... 

In the product-ion MS-MS spectra of dolasetron and metabolites (Ch. 10.3.2), an ion at m/z 166, representing the loss of the indole-3-caiboxylic acid, was found to be a common fragment ion. The precursor-ion analysis mode, with m/z 166 as common product ion, was applied to search for possible additional metabolites. All five previously identified metabolites were found, but no other compounds [9]. 

Increasing speed in data-acquisition on newer instruments enables more advanced DDA experiments to be performed. The use of automated DDA-MS-MS of multiple precursor ions on an ion-trap instrument is combined with a postacquisition search through the complete data set for specific neutral losses or common fragment ions. The method is applied to search for metabolites of MEN 15916 [42] and revealed both mono-, di-, and trihydroxy-metabohtes, as well as some unexpected metabolites (a carboxylic acid, a A-dealkylated metabolite, and its hydroxy-analog). 

Acylcamitine profiling by means of MS was first introduced by Millington and coworkers, using fast-atom bombardment (FAB) [59], ttiermospray [60], and/or continuous-flow FAB [61], In MS-MS, the acylcamitine or butyl-derivatized acylcamitine is fragmented to a common fragment ion at m/z 85, while the methyl-derivative is fragmented to an ion with m/z 99. 

Figure 12.3 Precursor-ion MS-MS acylcamitine profiles (common fragment ion m/z 85) with profiles from (a) a healthy newborn, (b) a newborn with MCAD deficiency (homozygous for A985G mutation), and (c) a newborn with MCAD deficiency (heterozygous for A985G mutation). Reprinted from [64] with permission. 1997, American Association for Clinical Chemistry.

---