Collisionally activated decompositions CAD

Collision of normal ions from the first quadrupole with gas molecules in the second quadrupole increases fragmentation, a process known as either collisionally induced dissociation (CID) or collisionally activated decomposition (CAD). 

An insight into the equilibria present in solutions of several complexes of the type (R3P)2HgX2 (X = C104, CF3COO) is provided by electrospray mass spectrometry (ES MS) (cf. Section 6.9.2.1.8). 39 In all cases the principal ions [(R3P)2HgX]+ are observed, even if these ions and other ionic constituents of the equilibria are known to be labile on the NMR timescale. In the presence of excess R3P the principal ions [(R3P)3HgX]+ appear. Also fragments of collisionally activated decomposition (CAD, can be influenced and controlled to some extent) are detected, e.g., [(R3P)HgX]+. 

Conventional ionization techniques like El or Cl are less well suited for the characterization of quaternary amines, which are the most common cationic surfactants. Because of their thermal instability and low volatility their corresponding mass spectra only show decomposition products and fragment ions which make it impossible to analyze environmental samples of unknown composition. By the use of EAB-MS and FD-MS, however, ionization of quaternary amines can be achieved without decomposition. FAB spectra are characterized by strong quasimolecular ions as well as structure specific ions. ° FAB in combination with collisionally activated decomposition (CAD) in a tandem mass spectrometer enables a clear differentiation between quasimolecular and fragment ions, which is often difficult using FAB alone. FD spectra of quaternary amines are dominated by quasimolecular ions as already described for other surfactant... 

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... 

A number of methods have been described for determination of tetracycline (chlortetracycline, tetracycline, and oxytetracycline) residues in tissues of food-producing animals (53-62), fish (63), eggs (64), and honey (65,66). Most of these methods use reversed-phase HPLC for determination. However, one uses TLC with UV densitometry ( ) and one uses GLC ( ), and one uses a direct mass spectrometric method CAD MIKE spectrometry (collisionally activated decomposition mass-analyzed ion kinetic spectrometry) for oxytetracycline in milk and meat (62). Several use solid-phase extraction in the cleanup procedure using XAD-2 resin (56,58) or Cj g cartridges... 

TD-IT, Thermal desorption-ion trap CAD MIKE, collisionally activated decomposition mass-analyzed ion kinetic energy MID, multiple ion detection FID, flame ionization detector NPD, nitrogen/phosphorus detector SIM, selected ion monitoring El, electron impact TMS, trimethylsilane MTBSTFA, N-methyl-N-(tetr.-butyldimethylsilyl)trifluoroacetamide. 

Applications of FAB have been succesfully performed in the characterization of a wide range of compounds (dyes, surfactants, polymers...) but little attention has been devoted to the capabilities of this technique to solve environmental concerns, such as organic pollutants identification in water. The widespread use of surfactants in the environment has required the emplo yment of both sensitive and specific methods for their determination at trace levels. GC/MS and HPLC procedures has been used for the determination of anionic (LAB s) and non ionic surfactants (NPEO) in water (1-4). Levsen et al (5) identified cationic and anionic sirrfactants in surface water by combined field desorption/ collisionally activated decomposition mass spectrometry (FD/CAD), whereas FAB mass spectrometry has been used for the characterization of pine industrial surfactants (6-8). 

Collision-induced dissociation (or decomposition), abbreviated CID. An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion during the collision of part of the translational energy of the ion to internal energy in the ion. The term collisional-activated dissociation (or decomposition), abbreviated CAD, is also used. 

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