Consecutive Dissociations Research Articles

Gas-phase behaviour of negative ions produced from thiazidic diuretics under electrospray conditions.

A systematic mass spectrometric study of 10 thiazidic diuretics and related compounds was undertaken by mass spectrometry (MS) with electrospray ionization in the negative ion mode. Collisional dissociation 'in-source' (CID-MS) and in a low-pressure collision cell (CID-MS/MS) were compared in both excitation regions. Spectra obtained by CID-MS and by CID-MS/MS were matched. Using the two methods, loss of HCl and consecutive dissociations from 2HCl losses were exhibited from compounds such as methyclothiazide and trichlormethiazide but not from other thiazidic diuretics that contain chlorine substituents in the aromatic moiety. However, deprotonated dichlorphenamide gave rise to loss of HCl by CID-MS and CID-MS/MS. For other diuretics such as hydroflumethiazide and hydrochlorothiazide, the loss of HCN and [HCN + SO(2)] was relevant. Reaction mechanisms were checked by means of deuterium-hydrogen exchange, which showed that deprotonation took place regioselectively on the heterocyclic moiety. The cleavage pathways require molecular isomerization forming ion-dipole complexes prior to decompositions, allowing long-distance proton transfer for neutral elimination. Identifications of the most specific fragmentations presented in this paper were applied to the screening and unambiguous identification of diuretics for horse doping control.

The determination of collisionally induced consecutive dissociations of ions by collision cell potential dependence

Consecutive two-step dissociations of parent ions inside and after a collision cell in the second field-free region of a reversed geometry mass spectrometer to give grand-daughter ions can be detected if a potential is applied to the collision cell. A quantitative method to assign the masses of the ions involved in the consecutive dissociations, based on the unique collision cell potential dependences of the kinetic energies of the grand-daughter ions formed, is presented. The practical utility of the method is examined for a parent anion and a parent cation. It is proven that in both cases consecutive dissociations occur which provide important information about the dissociation patterns of these parent ions. A brief comparison of the capability of the method to detect, distinguish and determine consecutive dissociations with that applied in three-sector instruments is also given. It is suggested that the method can yield additional information if only molecular or pseudo-molecular ions are generated in the ion source.

Consecutive collision-induced dissociations in Fourier transform mass spectrometry

Consecutive collision-induced dissociations in Fourier transform mass spectrometry

Consecutive unimolecular dissociations of fluorinated β-diketone chelates

The apparent one-step loss of a ligand in the mass spectral decomposition of tris-(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)aluminium is suggested to occur, rather, in two steps.