Characterization of Ions Activated by Collision-Induced Dissociation with Collision Energy Up to 30 eV Using 4-Trifluoromethyl-2,3,5,6-tetrafluorobenzylpyridinium "Thermometer Ion".

To facilitate the assessment of the internal energy distribution of ions activated by collision-induced dissociation with collision energy in the laboratory frame exceeding 20 eV, the screening of fluorine-containing benzylpyridiniums was performed by evaluating their dissociation energies through quantum chemistry calculations at the CCSD(T)/6-311++G(d,p)//M06-2X-D3/6-311++G(d,p) level of theory. The dissociation energy increased with the presence of a trifluoromethyl group at the 4-position and fluorine atoms at positions 2, 3, 5, and 6 of benzylpyridinium. However, the fluorine atom at the 4-position in benzylpyridinium slightly reduced the dissociation energy, suggesting its electron-donating nature. 4-Trifluoromethyl-2,3,5,6-tetrafluorobenzylpyridinium (CF₃,F₄-BnPy⁺) has the highest dissociation energy among the reported benzylpyridiniums and is a suitable thermometer ion for characterizing the internal energy distributions of ions activated by collision-induced dissociation (CID) during tandem mass spectrometry. Using CF₃,F₄-BnPy⁺ allowed the evaluation of the internal energy distribution of CID-activated ions up to a collision energy of 30 eV in the laboratory frame. The survival yield method using fluorine-substituted benzylpyridiniums and 4-methylbenzylpyridiniums facilitates the optimization of tandem mass spectrometry parameters for the analysis of small molecules, such as metabolites.