Secondary fragmentation

In the mass spectrum of 10-propyl-3-amino-7,9-dichlorophenothiazine-5-sulfone (67) the molecular ion is quite intense, but the base peak is formed by the loss of Et from the propyl side-chain16. The other primary and secondary fragmentations are summarized in equation (31). The loss of two OH radicals (H2Oz) can occur favorably from the extra configuration of 67 (cf. Section II.D). 

The mass spectra of TMS ethers are characterized by weak or absent molecular ions the [M-15] ion formed by cleavage of a methyl to silicon bond is generally more abundant. This ion can be used to determine the molecular weight provided that it is not mistaken for the molecular ion itself. Dissociation of the molecular ion often results in prominent secondary fragment ions containing the ionized dimethylsiloxy group attached to a hydrocarbon portion of the molecule. In common with alkyl ethers,... 

The above discussion pertains, principally, to primary fragments. Other techniques are currently available to estimate the velocity and range of secondary fragments. 

One of these, based on a semi-empirical relationship taken from Reference 12, predicts secondary fragment initial velocity ... 

V - Secondary fragment initial velocity, in/s Re Radius of spherical charge, inches... 

R Range from center of explosive charge to nearest face of secondary fragment, inches... 

Ap = Area of secondary fragment presented to explosive, ln gg Secondary fragment shape factor... 

In addition to its rather narrow limits of validity, this expression is strictly applicable only to spherical charges of Composition B. However, until further work is completed, this equation represents the best method available for predicting secondary fragment velocities. 

If the energy of the ionizing electrons is 13 eV (to minimize the secondary fragmentation processes), the intensities of the primary ions peaks with rn/z values 129, 115, and 101 will be 78%, 85%, and 100%, correspondingly. Theoretically calculated intensities should be (101/129) = 0.78 (78%) and (101/115) = 0.88 (88%). As one can see, the resulting values are fairly close to the theoretical ones. The estimation of the intensity of an ion peak resulting due to the loss of methyl radical has a value two to three times higher than the experimental one. 

Boesl, U. Weinkauf, R. Schlag, E. Re-flectron TOF-MS and Laser Excitation for the Analysis of Neutrals, Ionized Molecules and Secondary Fragments. Int. J. Mass Spectrom. Ion Proc. 1992, 772, 121-166. 

Secondary fragmentation Fragments produced by primary fragments striking objects and imparting explosive inertia to them. 

The nebulizer capillary position may be adjustable on a screw thread to permit optimization of sample uptake and drop size. Alternatively or additionally, an impact bead may be placed in the path of the initial aerosol to provide a secondary fragmentation and so improve the efficiency of nebulization. Such a device is illustrated in Fig. 2.9. 

Besides these primary reactions, various secondary reactions take place in which ions or excited molecules participate. The final resulf of these three events is that, through the diverse primary and secondary fragmentations, radicals are formed and fhe complefe cascade of reactions triggered by the primary excitation of molecules may take up to several seconds. The energy deposited does not always cause change in the precise position where it was originally deposited, and it can migrate and affect the product yield considerably. 

A relatively explicit nomenclature is used to characterise the type of ions formed singly charged, multiply charged, monoatomic, polyatomic, molecular, pseudo-molecular, parent, daughter, metastable, secondary fragments, etc. 

Before abandoning the idea, however, the work of Dejongh et al. was repeated. A lower ionization voltage was used to limit secondary fragmentation processes and hopefully to accentuate stereochemical differences. The 17 ev mass spectra of the pertrimethylsilylated derivatives of < - and / -D-glucopyranose are shown in Figure 6. The two spectra are very similar however, intensity differences do occur. In particular, attention has been focused on the ratio of the two peaks with m/e values of 435 and 393. The m/e 435 peak corresponds to the parent molecular ion (PMI) with loss of CH3 and TMSiOH, the 393 peak to the shard A minus CH3 (57). 

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