Investigation of the Collision-Induced Dissociation Mechanism of Protonated N,N,N',N'-Tetraoctyldiglycolamide With Infrared Ion Spectroscopy

Elucidation of gas-phase fragmentation mechanisms of fuel cycle molecules is critical for the development of untargeted analysis tools for understanding radiation chemistry in complex systems. The collision-induced dissociation (CID) fragmentation of protonated N,N,N',N'-tetraoctyldiglycolamide (TODGA) was studied using infrared ion spectroscopy (IRIS) in a quadrupole ion trap and with resonance ejection experiments in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. CID of protonated TODGA produced two fragments, one at m/z = 340 and one at m/z = 312. IRIS spectra of both products suggest that they have ring structures. While tandem mass spectrometry experiments suggested that m/z = 312 could have been produced via elimination of carbon monoxide from the ring in m/z = 340, resonance ejection experiments using the FT-ICR showed that the lower mass fragment is produced directly from protonated TODGA, at least at lower activation energies. Exploration of the fragmentation mechanism with density functional theory using N,N,N',N'-tetramethyldiglycolamide (TMDGA) as an analog of TODGA suggested that initial activation of protonated TMDGA results in cleavage of the carbon-nitrogen bond in the protonated amide group and cyclization of the remaining charged fragment, although the neutral amine remains closely bound. It is from this intermediate that the two observed fragmentation products are formed, either from elimination of the neutral amine or by elimination of carbon monoxide and the amine. A higher energy pathway was also found that formed the dimethyl analog of m/z = 312 from m/z = 340. This proposed mechanism is consistent with experimental IRIS measurements of protonated TODGA fragments, that they are both formed directly from protonated TODGA, and that m/z = 312 can also be formed from CID of m/z = 340.