Metastable linked scanning

The behavior of chloromethyl esters of -carboxylic acids CH3(CH2) COOCH2Cl (n -2-12) and of all their 66 monochlorinated derivatives was examined with the aid of metastable linked scan techniques207. The main fragmentations were discussed with attention to the McLafferty rearrangement, which gives rise to abundant product ions for all compounds with n > 2 except for those in which the chlorine substituent occupies positions 3 and 5 in the chain. 

Linked Scanning and Metastable Ions in Quadrupole Mass Spectrometry... 

The importance of linked scanning of metastable ions or of ions formed by induced decomposition is discussed in this chapter and in Chapter 34. Briefly, linked scanning provides information on which ions give which others in a normal mass spectrum. With this sort of information, it becomes possible to examine a complex mixture of substances without prior separation of its components. It is possible to look highly specifically for trace components in mixtures under circumstances in which other techniques could not succeed. Finally, it is possible to gain information on the molecular structures of unknown compounds, as in peptide and protein sequencing (see Chapter 40). 

The study of metastable ions concerns substances that have been ionized by electrons and have undergone fragmentation. The stable molecular ions that are formed by soft ionization methods (chemical ionization. Cl field ionization, FI) need a boost of extra energy to make them fragment, but in such cases other methods of investigation than linked scanning are generally used. 

Scanning for metastable ions requires adjustment of electric and magnetic fields which can be adjusted individually or in conjunction with each other. If two fields are automatically adjusted at the same time, it is known as linked scanning. It is important to remember that metastable ions are not the product ions m2 but are the ions undergoing fragmentation (precursor ions mj). 

By adjusting magnetic and electric fields in the ion optics (see Chapters 33 and 34 on linked scanning), metastable ions can be investigated. 

By linking the way in which the first and third quadrupoles are scanned, specific metastable fragments can be detected, which is one form of linked scanning. 

Again, as for metastable ions, linked scanning of the first and third quadrupoles reveals important information on fragmentation processes, viz., which normal ions fragment to give which product ions. 

Triple quadrupole instruments can be used to detect metastable ions or can be used for linked scanning to obtain information about molecular structure. 

Each of the fields V, E, and B can be varied by itself to examine metastable ions and their connections, but with modern automated techniques it is better to use linked scanning. 

By automating the linked scanning under computer control, a complete mass spectrum can be scanned for metastable ions in just a few seconds. 

Automated linked scanning of metastable ions is valuable for deducing a whole or partial molecular structure of an unknown substance. 

B. a term meaning the strength of a magnetic field, often used to refer to a magnetic field or sector B/E. a method of linked scanning for metastable ions, which uses combined m netic and electric fields B /E. a method of linked scanning for metastable ions, which uses combined magnetic and electric fields CAD. collisionally activated decomposition... 

EW. a method of linked scanning for metastable ions, which uses electric fields (see V)... 

Lacey, M.J. Macdonald, C.G. The Use of Two Linked Scanning Modes in Alternation to Analyze Metastable Peaks. Org. Mass Spectrom. 1980,15, 134-137. 

The electron impact-induced decomposition pathways of several structurally related /u.-methylene complexes of cobalt, rhodium, manganese, and iron have been elucidated by high resolution measurements, analysis of metastable transition (DADI linked scan), and 2H labeling (46). Terminal carbonyl ligands are generally lost prior to further fragmentation of the three-membered frameworks. Subsequent rearrangement reactions of the... 

McLafferty et al. (37) studied the collisionally activated dissociation (CAD) of the ions resulting from the fast-atom bombardment ionization of cyano- and methylcobalamins, using a tandem mass spectrometer. They showed that mlz 1329 is produced only from the quasi-molecular ion. Similar CAD spectra are produced by both the quasi-molecular ions and the 1329 peak, indicating that essentially all fragmentation arises from this latter ion. CAD spectra produced for the 1329 ion derived from methylcobalamin or vitamin B12 coenzyme are also similar. This is consistent with the work of Taylor (10), who used linked-scan metastable ion techniques in a conventional double-focusing mass spectrometer to show the same thing. The sequential... 

The controversy around the two possible origins of the BH ion (from direct pyrolysis or from the nucleoside-like ion) necessitated studies using linked scan techniques and metastable-ion mapping." From those results it is clear that the BH ions, as well as methylfuran particles, are formed directly by the pyrolitic process. 

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