Identification of Isomeric Tributylphosphate Dimers Formed by Radiolysis Using Tandem Mass Spectrometry and Stable Isotopic Labelling

Tributylphosphate (TBP) dimers, formed during radiolysis of the nuclear fuel reprocessing solvent, were studied using tandem mass spectrometry (MS/MS), stable isotopic labelling (2H) and synthetic model compounds. The structures of isomeric dimers and their lower homologues were established, using GC/MS as well as electron impact and chemical ionisation GC/tandem mass spectrometry, with an extensive use of ion chromatograms of characteristic fragment ions from collision-induced decomposition in both non-deuterated and selectively deuterated series. An explanation of isomer ratios and of the restricted number of lower homologues as well as a radiolytic mechanism are advanced. The TBP-dimer fraction represented less than ∼0.03% of the total mixture obtained from radiolysis of solvent.