Methane PICI spectrum

The methane PICI spectrum of TATP obtained with a linear quadrupole mass analyzer has been reported to contain ions of m/z 103,117,133, and 223, corresponding to the pseudomolecular ion [TATP -i- H]" [35]. A full-scan methane PICI spectrum of TATP has also been reported to contain ions of m/z 43(100%), 59,74,75,91, and 223(<5%), as shown in Figure 16.4B [30].The LOD for methane PICI analysis of TATP with linear qudaru-pole and ion trap mass analyzers were reported in the same work as 1 and 2 ng, respectively. Quantitation was based on extracted ions m/z 43, 59, 75, and 91 in both cases. When the m/z 91 ion was isolated in an ion trap mass analyzer and fragmented under CID, ions of m/z 43 and 74 were observed [30]. The third-order tandem mass spectrometry (MS ) experiment involving isolation of m/z 91 with subsequent CID and isolation of the m/z 74 product ion leads to the formation of a m/z 43 ion upon further CID. These results provide a scheme for analysis of TATP by selected reaction monitoring (SRM). 

Reactions 7.8 and 7.9). Figure 7.13b is the methane PICI spectrum of the same compound in which the [M- -H]+ cation (m/z 430) is the base peak (Reaction 7.12). Note there is less fragmentation in PICI as compared to El. Figure 7.13c is an example of a phenomenon called self-PICI, which can show up in spectra if the pressure of the reagent gas is low and the pressure of the sample molecules... 

TABLE 7.6 Effect of Ion Source Pressure on Methane PICI Spectrum for Di-n-Butyl Phthalate"... 

Example The extraordinary stable trityl ion, PhsC, m/z 243, tends to dominate mass spectra (Chap. 6.6.2). Thus, neither the El spectrum of chlorotriphenyl-methane nor that of its impurity triphenylmethanol show molecular ions (Fig. 8.11). An isobutane PICI spectrum also shows the trityl ion almost exclusively, although some hint is obtained from the Ph2COH ion, m/z 183, that cannot be explained as a fragment of a chlorotriphenylmethane ion. Only FD reveals the presence of the alcohol by its molecular ion at m/z 260 while that of the chloride is detected at m/z 278. Both molecular ions undergo some OH or Cl loss, respectively, to yield the Ph3C fragment ion of minor intensity. 

In Figure 7.13 examples of El, methane PICI and an interesting cation/molecule reaction called self-PICI are shown. Figure 7.13a is the 70 eV El spectrum of an aromatic compound in which the [M]+ cation (m/z 429) is not observed. For this molecule, the amount of internal energy retained by the [M]+ cation, after electron ionization, was so great that the [M]" " cation totally fragmented... 

FIGURE 7.18 (a) PICI spectrum of V-nitroso-di-n-propylamine (peak 4 in Figure 7.17a) with ammonia as the reagent gas. (b) PICI spectrum of V-nitroso-di-n-propy-lamine (peak 4 in Figure 7.17b) with isobutane as the reagent gas. (c) PICI spectrum of V-nitroso-di-n-propylamine (peak 4 in Figure 7.17c) with methane as the reagent gas. (Masucci and Caldwell, unpublished data.)... 

Example El vs. methane reagent gas PICI spectrum of methionine. The comparison shows greatly reduced fragmentation in the PICI spectrum (Fig. 7.4). Only small intact molecules such as NH3, HCOOH, and MeSH are eliminated from the [Mh-H]" ion, m/z 150, which yields the base peak. In addition, the PICI spectrum perfectly reveals the isotopic pattern that indicates the presence of sulfur. The horizontal line (Fig. 7.4b) means that this range was not acquired in the PICI spectrum as to keep the spectrum free from reactant ion signals. The spectra were, however, plotted on the same m/z scales to simplify the comparison. 

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