Influence of Background H 2 O on the Collision-Induced Dissociation Products Generated from [UO 2 NO 3 ] +

Abstract

Developing a comprehensive understanding of the reactivity of uranium-containing species remains an important goal in areas ranging from the development of nuclear fuel processing methods to studies of the migration and fate of the element in the environment. Electrospray ionization (ESI) is an effective way to generate gas-phase complexes containing uranium for subsequent studies of intrinsic structure and reactivity. Recent experiments by our group have demonstrated that the relatively low levels of residual H 2 O in a 2-D, linear ion trap (LIT) make it possible to examine fragmentation pathways and reactions not observed in earlier studies conducted with 3-D ion traps (Van Stipdonk et al. J. Am. Soc. Mass Spectrom. 14, 1205–1214, 2003). In the present study, we revisited the dissociation of complexes composed of uranyl nitrate cation [U VI O 2 (NO 3 )] + coordinated by alcohol ligands (methanol and ethanol) using the 2-D LIT. With relatively low levels of background H 2 O, collision-induced dissociation (CID) of [U VI O 2 (NO 3 )] + primarily creates [UO 2 (O 2 )] + by the ejection of NO. However, CID (using He as collision gas) of [U VI O 2 (NO 3 )] + creates [UO 2 (H 2 O)] + and UO 2+ when the 2-D LIT is used with higher levels of background H 2 O. Based on the results presented here, we propose that product ion spectrum in the previous experiments was the result of a two-step process: initial formation of [U VI O 2 (O 2 )] + followed by rapid exchange of O 2 for H 2 O by ion-molecule reaction. Our experiments illustrate the impact of residual H 2 O in ion trap instruments on the product ions generated by CID and provide a more accurate description of the intrinsic dissociation pathway for [U VI O 2 (NO 3 )] + . [Figure not available: see fulltext.].