Collision-induced dissociation of [U O (ClO )] revisited: Production of [U O (Cl)] and subsequent hydrolysis to create [U O (OH)].

Rationale: In a previous study [Rapid Commun Mass Spectrom. 2004;18:3028-3034], collision-induced dissociation (CID) of [U O (ClO )] appeared to be influenced by the high levels of background H O in a quadrupole ion trap. The CID of the same species was re-examined here with the goal of determining whether additional, previously obscured dissociation pathways would be revealed under conditions in which the level of background H O was lower.

Methods: Water- and methanol-coordinated [U O (ClO )] precursor ions were generated by electrospray ionization. Multiple-stage tandem mass spectrometry (MS ) for CID and ion-molecule reaction (IMR) studies was performed using a linear ion trap mass spectrometer.

Results: Under conditions of low background H O, CID of [U O (ClO )] generates [U O (Cl)] , presumably by elimination of two O molecules. Using low isolation/reaction times, we found that [U O (Cl)] will undergo an IMR with H O to generate [U O (OH)] .

Conclusions: With lower levels of background H O, CID experiments reveal that the intrinsic dissociation pathway for [U O (ClO )] leads to [U O (Cl)] , apparently by loss of two O molecules. We propose that the results reported in the earlier CID study reflected a two-step process: initial formation of [U O (Cl)] by CID, followed by a very rapid hydrolysis reaction to leave [U O (OH)] .