Study of mass spectrometric fragmentations of tributyl phosphate via collision‐induced dissociation

Abstract

Tributyl phosphate (TBP) fragmentation mechanisms were studied by mass spectrometry (MS) and tandem mass spectrometry (MS/MS), using electron impact (EI) or chemical (CI) ionisation of the parent compound and its deuterated analogues. The study of this simple compound is essential for the analysis of complex post-radiolysis mixtures and the identification of particular effects arising from the radiolysis or acid hydrolysis of TBP during nuclear fuel reprocessing. Energy-resolved mass spectrometry (ERMS) and isotopic labelling helped to establish the fragment ion connectivities by distinct identification of the competitive and consecutive mechanisms. An ion-dipole intermediate hypothesis, proposed previously in the case of alkyl phosphates and phosphonates in order to explain the mobility of hydrogen atoms from the alkyl chains, is rejected on the basis of the identification of competitive mechanisms in the TBP fragmentation pathways. Copyright The detailed knowledge of these mechanisms can enable the design of new improved solvent systems, as well as improvements in the reprocessing procedures from the study of these compounds unwanted even at trace levels. In this study, we report an investigation by tandem mass spectrometry (MS/MS) of protonated or deuterated tributyl phosphate and its derivatives, by comparing collisioninduced decomposition (CID) of specifically labelled compounds. In a following paper, we will report CID of protonated (or deuterated) TBP dimers formed by radiolytic degradation, which are important because these compounds are potential complexing agents of plutonium. 6 In a previous paper, 7 the structural identification of isomeric TBP dimers was emphasised as a necessary step to understood their behaviour. All of these results, concerning structural identification of TBP dimers and CID of protonated TBP, allow better investigation of minor functionalised degradation product structures generated by radiolysis, as reported in a previous paper. 8The mass spectrum of TBP obtained under EI conditions includes fragment ions involving consecutive losses of butene together with formation of alkyl carbocations. 14 When studied using a high-pressure CI/NH 3 source, the loss of the alkene chain from TBP 15 or other phosphates can be rationalised by a single H-transfer within the MH ion.Under these conditions, poor intensities of fragment ions are observed because of the low energy deposited on the MH ion. However, the high abundance of MH ions easily allows CID studies of these ions. Leroy has studied the CID fragmentation of protonated phosphonates prepared under ammonia chemical ionisation conditions. 16 These results enabled establishment of the proton affinity scale for some phosphonates using Cooks'

Identification tree based on fragmentation rules for structure elucidation of organophosphorus esters by electrospray mass spectrometry

“…The generic fragmentation rules developed from previous results allow the development of a systematic approach to the identification. Data complementary to our experimental findings concerning fragmentations are found in the literature of other protonated organophosphorus esters.…”

“…Following this example, all other phosphonate and phosphate esters in this study were investigated in an analogous way. The fragmentation rules proposed for the ensemble of these compounds (Tables and ) were deduced from the experimental results presented here, our previously obtained data, as well as results published by others . A new nomenclature was created in order to give clarity to the specific fragmentation rules.…”

“…Collision‐induced dissociation (CID) data and fragmentation pathways were retrieved from previous work performed in our laboratory (40 entries) and from the research literature (15 entries) …”

9 Organic gas phase ion chemistry

“…In a separate study, the fragmentation of protonated tributylphosphate, (C 4 H 9 O) 3 POH ϩ , was investigated. 210 Energy-resolved mass spectrometry and isotope labelling experiments allowed both competitive and consecutive mechanisms to be identified. The unimolecular gas phase chemistry of (CH Ϫ was found to be in equilibrium with a stable ion-neutral association complex, and products were formed via a bimolecular reaction of a second neutral with this complex.…”

Characterization of alkylphosphonic acid vapors using atmospheric flow tube–ion trap mass spectrometry

“…Along with being the first reported use of nitrate anion adduction for the analysis of vaporized organophosphorus compounds (OPCs), this article presents groundwork toward characterizing anionic adducts of OPCs in the gas phase as opposed to only cationic OPC adduct species. Work by Ewing and Valenzuela, for example, focused on the analysis of dimethyl methylphosphonate and tributyl phosphate, both of which have high proton affinities ( ca 900 kJ/mol) ; like those two OPCs, phosphonic acids also generally have higher proton affinities . Finally, the initial work demonstrating the possible quantification of MPA, EPA, PPA, and tBPA from headspace over solutions by AFT‐MS and potential ways to improve linear ranges in future applications is reported in this article.…”