Fragmentation rules

A fragment is an atom or group of atoms bounded by ICs and all except hydrogen are considered polar. A fragment may have many internal bonds, but those connecting it to ICs are called valence bonds. Valence bonds are most often single, but can be aromatic. Polar fragments can interact in various ways. 

To quantitate this interaction, several types of polar fragments need to be defined  

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Whereas the components of (known) test mixtures can be attributed on the basis of APCI+/, spectra, it is quite doubtful that this is equally feasible for unknown (real-life) extracts. Data acquisition conditions of LC-APCI-MS need to be optimised for existing universal LC separation protocols. User-specific databases of reference spectra need to be generated, and knowledge about the fragmentation rules of APCI-MS needs to be developed for the identification of unknown additives in polymers. Method development requires validation by comparison with established analytical tools. Extension to a quantitative method appears feasible. Despite the current wide spread of LC-API-MS equipment, relatively few industrial users, such as ICI, Sumitomo, Ford, GE, Solvay and DSM, appear to be somehow committed to this technique for (routine) polymer/additive analysis. 

In addition to the searchable library compilations, several compendial books on the electron ionization fragmentation behavior of compounds have been published [34-36]. They are dated, but nevertheless effectively capture the collective fragmentation information prior to their publication. All of these information sources discuss electron ionization spectra. El fragmentation rules, however, can be of limited assistance in interpreting soft ionization and MS-MS product ion spectra. 

It should be kept in mind that the fragmentation rules above apply to El mass spectrometry. Since other ionizing (Cl, etc.) techniques often produce molecular ions with much lower energy or quasimolecular ions with very different fragmentation patterns, different rules govern the fragmentation of these molecular ions. 

We expect that over the next decade a similar trend will occur with other classes of compounds. This requires, however, a large joint research effort by many groups. Most importantly, sets of isomeric reference standards must become available, and their spectra recorded, rationalized, and turned into generally applicable fragmentation rules that can be understood and applied by all practicing chemists. 

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